potential for causing injury to life or damage to property or the environment. Weather is not .... Wildfires, such as Australian bushfires, are more common during times of drought. Causes ...... It received the name "Wizard's Eye" because it looks like an eye. ...... In 1900, Nikola Tesla generated artificial lightning by using a large.
ANAND AGRICULTURAL UNIVERSITY B.A. COLLEGE OF AGRICULTURE ANAND – 388110
AN ASSIGNMENT ON
Crop Protection From Weather Hazards AGMET-705, Applied Agrometeorology (3+0)
SUBMITTED TO
DR. H. R. PATEL AGROMETEOROLOGIST, DEPT. OF AGRICULTURAL METEOROLOGY,
B.A.C.A., AAU, ANAND SUBMITTED BY
DIVESH CHOUDHARY M. Sc. (Agri.) III Sem, Reg. No: 04-0922-09
DEPT. OF AGRICULTURAL METEOROLOGY B.A. COLLEGE OF AGRICULTURE ANAND AGRICULTURAL UNIVERSITY ANAND -388 110
Weather hazards A hazard may be defined as “a dangerous condition or event that threat or have potential for causing injury to life or damage to property or the environment. Weather is not always normal. Some abrupt or sudden changes take place in weather which are called weather abnormalities. They cause considerable damage to the crops. Some of them are floods, droughts, untimely rains, thunder storms, hail storms and dust storms, cold waves accompanied by frost, heat waves, high winds and cyclones. Weather is the dominant factor determining the success or failure of agricultural enterprises. This is because farmers have no control over this natural force. Weather manifests its influence on agricultural operations and farm production through its effects on soil, plant growth as well as on every phase of animal growth and development. Out of the total annual crop losses, a greater portion is because of aberrant weather. Several years ago, it was estimated in the United States that annual losses in agriculture are 13 billion dollars; out of this amount about 11 percent are caused directly by weather hazards like floods, hailstones and storms. At the same time, losses due to conditions affecting harvesting, storage, parasites, crop and animal diseases are highly influenced by weather. In all, directly and indirectly, weather makes a contribution of approximately three fourth of the annual losses in the farm production. Types of weather hazards Manmade hazards Manmade hazards are hazards, which hare due to human negligence. Manmade hazards are associated with industries or energy generation facilities and include explosions, leakage of toxic waste, pollution, dam failure, wars or civil strife etc. Natural hazards Natural hazards are hazards, which are caused because of natural phenomena (hazards with meteorological, geological or even biological origin). Examples of natural hazards are cyclones, tsunamis, earthquake and volcanic eruption which are exclusively of natural origin. Landslides, floods, drought, fires are socio-natural hazards since their causes are both natural and manmade. For example flooding may be caused because of heavy rains, landslide or blocking of drains.
Main natural hazards in India, a country with diverse hypsographic and climatologically conditions, 70 per cent of the cultivable land is prone to drought, 60 per cent of the land area is prone to earthquake, 12 per cent to Floods, 8 per cent to Cyclones, 85 per cent of the land area is vulnerable to number of natural hazards and 22 States are categorized as multi hazards States. Tens of thousands of people are affected by natural disasters. In the recent past the country suffered impact of earthquake even where the seismicity was low as per the seismic zoning map, as in the case of Maharastra and droughts have occurred in the areas with highest rainfall i.e. Cherrapunji in the North East. The 1999 Super Cyclone of Orissa and 2001 Earthquake of Gujarat have inflicted untold misery. Major natural hazards include droughts, floods, earthquakes, and tropical cyclones and minor ones include landslides, hailstorms, avalanches, bushfires and forest fires. These disasters take a heavy toll on human lives and resources causing economic, environment and social losses. Natural disasters affect the rural community the most, as they are vulnerable to economic changes, and have no alternate means of livings. Natural disasters destroy infrastructure, cause mass migration, reduction in food and fodder supplies and sometimes leads to drastic situations like starvation. To deal with such disasters it is essential to work with preparedness agenda with long-term relief and rehabilitation focus. (Sharma, 2009). Rainfall associated such natural disaster have impact over India on reoccurring basis. One of the major disaster is landslide (Jamir et al; 2008)., others are flood and drought. 1) Droughts; 2) Frost; 3) Floods; 4) Locust; 5) Cyclone; 6) Fog; 7) Storm; 8) Heat waves; 9) Extreme weather.
A) Drought A drought (or drought [archaic]) is an extended period of months or years when a region notes a deficiency in its water supply. Generally, this occurs when a region receives consistently below average precipitation. It can have a substantial impact on the ecosystem and agriculture of the affected region. Although droughts can persist for several years, even a short, intense drought can cause significant damage and harm the local economy. This global phenomenon has a widespread impact on agriculture. The United Nations estimates that an area of fertile soil the size of Ukraine is lost every year because of drought, deforestation, and climate instability. Lengthy periods of drought have long been a key trigger for mass migration and played a key role in a number of ongoing migrations and other humanitarian crises in the Horn of Africa and the Sahel.
Consequences Periods of drought can have significant environmental, agricultural, health, economic and social consequences. The effect varies according to vulnerability. For example, subsistence farmers are more likely to migrate during drought because they do not have alternative food sources. Areas with populations that depend on subsistence farming as a major food source are more vulnerable to drought-triggered famine. Drought can also reduce water quality, because lower water flows reduce dilution of pollutants and increase contamination of remaining water sources. Common consequences of drought include:
Diminished crop growth or yield productions and carrying capacity for livestock Dust bowls, themselves a sign of erosion, which further erode the landscape Dust storms, when drought hits an area suffering from desertification and erosion Famine due to lack of water for irrigation Habitat damage, affecting both terrestrial and aquatic wildlife Malnutrition, dehydration and related diseases Mass migration, resulting in internal displacement and international refugees Reduced electricity production due to insufficient available coolant for power stations, and reduced water flow through hydroelectric dams Shortages of water for industrial users Snakes migration and increases in snakebites Social unrest War over natural resources, including water and food Wildfires, such as Australian bushfires, are more common during times of drought
Causes Generally, rainfall is related to the amount of water vapor in the atmosphere, combined with the upward forcing of the air mass containing that water vapor. If either of these is reduced, the result is a drought. This can be triggered by an above average prevalence of high pressure systems, winds carrying continental, rather than oceanic air masses (i.e. reduced water content), and ridges of high pressure areas form with behaviors which prevent or restrict the developing of thunderstorm activity or rainfall over one certain region. Oceanic
and atmospheric weather cycles such as the El Niño-Southern Oscillation (ENSO) make drought a regular recurring feature of the Americas along the Pacific coast and Australia. Guns, Germs, and Steel author Jared Diamond sees the stark impact of the multi-year ENSO cycles on Australian weather patterns as a key reason that Australian aborigines remained a hunter-gatherer society rather than adopting agriculture. Another climate oscillation known as the North Atlantic Oscillation has been tied to droughts in northeast Spain. Human activity can directly trigger exacerbating factors such as over farming, excessive irrigation, deforestation, and erosion adversely impact the ability of the land to capture and hold water. While these tend to be relatively isolated in their scope, activities resulting in global climate change are expected to trigger droughts with a substantial impact on agriculture throughout the world, and especially in developing nations. Overall, global warming will result in increased world rainfall. Along with drought in some areas, flooding and erosion will increase in others. Paradoxically, some proposed solutions to global warming that focus on more active techniques, solar radiation management through the use of a space sunshade for one, may also carry with them increased chances of drought.
Types of drought As a drought persists, the conditions surrounding it gradually worsen and its impact on the local population gradually increases. People tend to define droughts in three main ways: 1. Meteorological drought Meteorological drought is brought about when there is a prolonged period with less than average precipitation. Meteorological drought usually precedes the other kinds of drought. 2. Agricultural droughts Agricultural drought is droughts that affect crop production or the ecology of the range. This condition can also arise independently from any change in precipitation levels when soil conditions and erosion triggered by poorly planned agricultural endeavors cause a shortfall in water available to the crops. However, in a traditional drought, it is caused by an extended period of below average precipitation. 3. Hydrological drought Hydrological drought is brought about when the water reserves available in sources such as aquifers, lakes and reservoirs fall below the statistical average. Hydrological drought tends to show up more slowly because it involves stored water that is used but not replenished. Like an agricultural drought, this can be triggered by more than just a loss of rainfall. For instance, Kazakhstan was recently awarded a large amount of money by the World Bank to restore water that had been diverted to other nations from the Aral Sea under Soviet rule. Similar circumstances also place their largest lake, Balkhash, at risk of completely drying out.
Mitigation strategies
Cloud seeding - an artificial technique to induce rainfall. Desalination of sea water for irrigation or consumption. Drought monitoring - Continuous observation of rainfall levels and comparisons with current usage levels can help prevent man-made drought. For instance, analysis of water usage in Yemen has revealed that their water table (underground water level) is put at grave risk by over-use to fertilize their Khat crop. Careful monitoring of moisture levels can also help predict increased risk for wildfires, using such metrics as the Keetch-Byram Drought Index or Palmer Drought Index. Land use - Carefully planned crop rotation can help to minimize erosion and allow farmers to plant less water-dependent crops in drier years. Rainwater harvesting - Collection and storage of rainwater from roofs or other suitable catchments. Recycled water - Former wastewater (sewage) that has been treated and purified for reuse. Transvasement - Building canals or redirecting rivers as massive attempts at irrigation in drought-prone areas. Outdoor water-use restriction - Regulating the use of sprinklers, hoses or buckets on outdoor plants, filling pools, and other water-intensive home maintenance tasks.
B) Frost Frost is the solid deposition of water vapor from saturated air. It is formed when solid surfaces are cooled to below the dew point of the adjacent air as well as below the freezing point of water. Frost crystals' size differ depending on time and water vapour available. Frost is also usually translucent in appearance. There are many types of frost, such as radiation and window frost. Frost causes economic damage when it destroys plants or hanging fruits.
Formation If a solid surface is chilled below the dew point of the surrounding air and the surface itself is colder than freezing, frost will form on the surface. Frost consists of spicules of ice which grow out from the solid surface. The size of the crystals depends on time, temperature, and the amount of water vapor available. Based on wind direction, "Frost arrows" might form. In general, for frost to form the deposition surface must be colder than the surrounding air. For instance frost may be observed around cracks in cold wooden sidewalks when moist air escapes from the ground below. Other objects on which frost tends to form are those with low specific heat or high thermal emissivity, such as blackened metals; hence the accumulation of frost on the heads of rusty nails. The apparently erratic occurrence of frost in adjacent localities is due partly to differences of elevation, the lower areas becoming colder on calm nights. It is also affected by differences in absorptivity and specific heat of the ground which in the absence of wind greatly influences the temperature attained by the superincumbent air. The formation of frost is an example of meteorological deposition.
Types of frost Radiation frost (also called hoar frost or hoarfrost or pruina) refers to the white ice crystals, loosely deposited on the ground or exposed objects that form on cold clear nights when heat losses into the open skies cause objects to become colder than the surrounding air. A related effect is flood frost which occurs when air cooled by ground-level radiation losses travels downhill to form pockets of very cold air in depressions, valleys, and hollows. Hoar frost can form in these areas even when the air temperature a few feet above ground is well above freezing. Nonetheless the frost itself will be at or below the freezing temperature of water. Hoar frost may have different names depending on where it forms. For example, air hoar is a deposit of hoar frost on objects above the surface, such as tree branches, plant stems, wires; surface hoar is formed by fernlike ice crystals directly deposited on snow, ice or already frozen surfaces; crevasse hoar consists in crystals that form in glacial crevasses where water vapour can accumulate under calm weather conditions; depth hoar refers to cup shaped, faceted crystals formed within dry snow, beneath the surface. Surface hoar is a cause of avalanches when it forms on top of snow. Conditions that are ideal are cold clear nights, with a very light wind that is able to circulate more humidified air around the snow surface. Wind that is too abrupt will destroy the crystals. When buried by subsequent snows they may remain standing for easy identification, or become laid down, but still dangerous because of the weakness of the crystals. In low temperatures surface hoar can also be broken apart and blown across the surface forming yukimarimo. Hoar frost also occurs around man-made environments such as freezers or industrial cold storage facilities. It occurs in adjacent rooms that are not well insulated against the cold or around entry locations where humidity and moisture will enter and freeze instantly depending on the freezer temperature.
Advection frost Advection frost (also called wind frost) refers to tiny ice spikes forming when there is a very cold wind blowing over branches of trees, poles and other surfaces. It looks like rimming the edge of flowers and leaves and usually it forms against the direction of the wind. It can occur at any hour of day and night.
Frost flowers Frost flowers occur when there is a freezing weather condition but the ground is not already frozen. The water contained in the plant stem expands and causes long cracks along the stem. Water, via capillary action, goes out from the cracks and freezes on contact with the air. Also the frost can literally look like a flower, even a dead flower from the previous summer. These are rare and wonderful to see as they are very delicate and last usually less than a day. Due to their fleeting nature, they are difficult to find to photograph and the locations of these Frost Flowers are elusive as terrain plays a big part in their formation as well.
Window frost Window frost (also called fern frost) forms when a glass pane is exposed to very cold air on the outside and moderately moist air on the inside. If the pane is not a good insulator (such as a single pane window), water vapour condenses on the glass forming patterns. With very low temperatures outside frost can appear on the bottom of the window even with double pane energy efficient windows, due to air convection between two panes of glass. The bottom part of the glazing unit is always colder than the top part. The glass surface influences the shape of crystals, so imperfections, scratches or dust can modify the way ice nucleates. If the indoor air is very humid, rather than moderately so, water would first condense in small droplets and then freeze into clear ice.
Rime Rime is a type of frost that occurs quickly, often under conditions of heavily saturated air and windy conditions. Ships travelling through Arctic seas may accumulate rime on the rigging. Unlike hoar frost, which has a feathery appearance, rime generally has an icy solid appearance. In contrast to the formation of hoar frost, in which the water vapour condenses slowly and directly into icy feathers, Rime typically goes through a liquid phase where the surface is wet by condensation before freezing.
Effect on plants Many plants can be damaged or killed by freezing temperatures or frost. This will vary with the type of plant and tissue exposed to low temperatures.
Tender plants, like tomatoes, die when they are exposed to frost. Hardy plants, like radish, tolerate lower temperatures. Perennials, such as the hosta plant, become dormant after first frosts and regrow when spring arrives. The entire visible plant may turn completely brown until the spring warmth, or will drop all of its leaves and flowers, leaving the stem and stalk only. Evergreen plants, such as pine trees, will withstand frost although all or most growth stops. Frost crack is a bark defect caused by a combination of low temperatures and heat from the winter sun. Vegetation will not necessarily be damaged when leaf temperatures drop below the freezing point of their cell contents. In the absence of a site nucleating the formation of ice crystals, the leaves remain in a super cooled liquid state, safely reaching temperatures of −4°C to −12°C. However, once frost forms, the leaf cells may be damaged by sharp ice crystals. Hardening is the process by which a plant becomes tolerant to low temperatures. See also cryobiology. Certain bacteria, notably Pseudomonas syringae, are particularly effective at triggering frost formation, raising the nucleation temperature to about −2°C. Bacteria lacking ice nucleation-active proteins (ice-minus bacteria) result in greatly reduced frost damage.
Protection methods The Selective Inverted Sink prevents frost by drawing cold air from the ground and blowing it up through a chimney. It was originally developed to prevent frost damage to citrus fruits in Uruguay. In New Zealand, helicopters are used in a similar function, especially in the vineyard regions like Marlborough. By dragging down warmer air from the inversion layers, and preventing the ponding of colder air on the ground, the low-flying helicopters prevent damage to the fruit buds. As the operations are conducted at night, and have in the past involved up to 130 aircraft per night in one region, safety rules are strict.
C) Floods A flood is an overflow of an expanse of water that submerges land. The EU Floods directive defines a flood as a temporary covering by water of land not normally covered by water. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Flooding may result from the volume of water within a body of water, such as a river or lake, which overflows or breaks levees, with the result that some of the water escapes its usual boundaries. While the size of a lake or other body of water will vary with seasonal changes in precipitation and snow melt, it is not a significant flood unless such escapes of water endanger land areas used by man like a village, city or other inhabited area. Floods can also occur in rivers, when flow exceeds the capacity of the river channel, particularly at bends or meanders. Floods often cause damage to homes and businesses if they are placed in natural flood plains of rivers. While flood damage can be virtually eliminated by moving away from rivers and other bodies of water, since time out of mind, people have lived and worked by the water to seek sustenance and capitalize on the gains of cheap and easy travel and commerce by being near water. That humans continue to inhabit areas threatened by flood damage is evidence that the perceived value of living near the water exceeds the cost of repeated periodic flooding. The word "flood" comes from the Old English flod, a word common to Germanic languages (compare German Flut, Dutch vloed from the same root as is seen in flow, float; also compare with Latin fluctus, flumen). Deluge myths are mythical stories of a great flood sent by a deity or deities to destroy civilization as an act of divine retribution, and are featured in the mythology of many cultures. Contemporary picture of the Burchardi flood that struck the North Sea coast of Germany and Denmark on the night between the 11 and 12 October 1634.
Principal types and causes of flood Riverine
Slow kinds: Runoff from sustained rainfall or rapid snow melt exceeding the capacity of a river's channel. Causes include heavy rains from monsoons, hurricanes and tropical depressions, foreign winds and warm rain affecting snow pack. Unexpected
drainage obstructions such as landslides, ice, or debris can cause slow flooding upstream of the obstruction. Fast kinds: include flash floods resulting from convective precipitation (intense thunderstorms) or sudden release from an upstream impoundment created behind a dam, landslide, or glacier.
Estuarine
Commonly caused by a combination of sea tidal surges caused by storm-force winds. A storm surge, from either a tropical cyclone or an extratropical cyclone, falls within this category.hi
Coastal
Caused by severe sea storms, or as a result of another hazard (e.g. tsunami or hurricane). A storm surge, from either a tropical cyclone or an extratropical cyclone, falls within this category.
Catastrophic
Caused by a significant and unexpected event e.g. dam breakage, or as a result of another hazard (e.g. earthquake or volcanic eruption).
Muddy
A muddy flood is generated by run off on crop land.
A muddy flood is produced by an accumulation of runoff generated on cropland. Sediments are then detached by runoff and carried as suspended matter or bedload. Muddy runoff is more likely detected when it reaches inhabited areas. Muddy floods are therefore a hillslope process, and confusion with mudflows produced by mass movements should be avoided. Other
Floods can occur if water accumulates across an impermeable surface (e.g. from rainfall) and cannot rapidly dissipate (i.e. gentle orientation or low evaporation). A series of storms moving over the same area. Dam-building beavers can flood low-lying urban and rural areas, often causing significant damage.
Effects i) Primary effects of flood
Physical damage - Can damage any type of structure, including bridges, cars, buildings, sewerage systems, roadways, and canals.
Casualties - People and livestock die due to drowning. It can also lead to epidemics and waterborne diseases.
ii) Secondary effects of flood
Water supplies - Contamination of water. Clean drinking water becomes scarce. Diseases - Unhygienic conditions. Spread of water-borne diseases. Crops and food supplies - Shortage of food crops can be caused due to loss of entire harvest. However, lowlands near rivers depend upon river silt deposited by floods in order to add nutrients to the local soil. Trees - Non-tolerant species can die from suffocation.
iii) Tertiary/long-term effects
Economic - Economic hardship, due to: temporary decline in tourism, rebuilding costs, food shortage leading to price increase, etc.
Control In many countries across the world, rivers prone to floods are often carefully managed. Defences such as levees, bunds, reservoirs, and weirs are used to prevent rivers from bursting their banks. When these defences fail, emergency measures such as sandbags or portable inflatable tubes are used. Coastal flooding has been addressed in Europe and the Americas with coastal defences, such as sea walls, beach nourishment, and barrier islands. Europe Remembering the misery and destruction caused by the 1910 Great Flood of Paris, the French government built a series of reservoirs called Les Grands Lacs de Seine (or Great Lakes) which helps remove pressure from the Seine during floods, especially the regular winter flooding. London is protected from sea flooding by a huge mechanical barrier across the River Thames, which is raised when the sea water level reaches a certain point (see Thames Barrier). Venice has a similar arrangement, although it is already unable to cope with very high tides; a new system of variable-height dikes is under construction. The defences of both London and Venice would be rendered inadequate if sea levels were to rise. The Adige in Northern Italy was provided with an underground canal that allows to drain part of its flow into the Garda Lake (in the Po drainage basin), thus lessening the risk of estuarine floods. The underground canal has been used twice, in 1966 and 2000. The largest and most elaborate flood defences can be found in the Netherlands, where they are referred to as Delta Works with the Oosterschelde dam as its crowning achievement. These works were built in response to the North Sea flood of 1953 of the southwestern part of the Netherlands. The Dutch had already built one of the world's largest dams in the north of the country: the Afsluitdijk (closing occurred in 1932).
Currently the Saint Petersburg Flood Prevention Facility Complex is to be finished by 2008, in Russia, to protect Saint Petersburg from storm surges. It also has a main traffic function, as it completes a ring road around Saint Petersburg. Eleven dams extend for 25.4 kilometres and stand eight metres above water level. In Austria, flooding for over 150 years, has been controlled by various actions of the Vienna Danube regulation, with dredging of the main Danube during 1870-75, and creation of the New Danube from 1972-1988. In Northern Ireland flood risk management is provided by Rivers Agency. Americas Another elaborate system of floodway defences can be found in the Canadian province of Manitoba. The Red River flows northward from the United States, passing through the city of Winnipeg (where it meets the Assiniboine River) and into Lake Winnipeg. As is the case with all north-flowing rivers in the temperate zone of the Northern Hemisphere, snowmelt in southern sections may cause river levels to rise before northern sections have had a chance to completely thaw. This can lead to devastating flooding, as occurred in Winnipeg during the spring of 1950. To protect the city from future floods, the Manitoba government undertook the construction of a massive system of diversions, dikes, and floodways (including the Red River Floodway and the Portage Diversion). The system kept Winnipeg safe during the 1997 flood and which devastated many communities upriver from Winnipeg, including Grand Forks, North Dakota and Ste. Agathe, Manitoba. It also kept Winnipeg safe during the 2009 flood. In the U.S., the New Orleans Metropolitan Area, 35% of which sits below sea level, is protected by hundreds of miles of levees and flood gates. This system failed catastrophically, in numerous sections, during Hurricane Katrina, in the city proper and in eastern sections of the Metro Area, resulting in the inundation of approximately 50% of the metropolitan area, ranging from a few centimetres to 8.2 metres (a few inches to 27 feet) in coastal communities. In an act of successful flood prevention, the Federal Government of the United States offered to buy out flood-prone properties in the United States in order to prevent repeated disasters after the 1993 flood across the Midwest. Several communities accepted and the government, in partnership with the state, bought 25,000 properties which they converted into wetlands. These wetlands act as a sponge in storms and in 1995, when the floods returned, the government did not have to expend resources in those areas. Asia In India, Bangladesh and China (i.e.,in the Grand Canal of China region) , flood diversion areas are rural areas that are deliberately flooded in emergencies in order to protect cities. Many have proposed that loss of vegetation (deforestation) will lead to a risk increase. With natural forest cover the flood duration should decrease. Reducing the rate of deforestation should improve the incidents and severity of floods.
Africa In Egypt, both the Aswan Dam (1902) and the Aswan High Dam (1976) have controlled various amounts of flooding along the Nile river.
Clean-up safety Clean-up activities following floods often pose hazards to workers and volunteers involved in the effort. Potential dangers include: water polluted by mixing with and causing overflows from sanitary sewers, electrical hazards, carbon monoxide exposure, musculoskeletal hazards, heat or cold stress, motor vehicle-related dangers, fire, drowning, and exposure to hazardous materials. Because flooded disaster sites are unstable, clean-up workers might encounter sharp jagged debris, biological hazards in the flood water, exposed electrical lines, blood or other body fluids, and animal and human remains. In planning for and reacting to flood disasters, managers provide workers with hard hats, goggles, heavy work gloves, life jackets, and watertight boots with steel toes and insoles.
Benefits There are many disruptive effects of flooding on human settlements and economic activities. However, floods (in particular the more frequent/smaller floods) can bring many benefits, such as recharging ground water, making soil more fertile and providing nutrients in which it is deficient. Flood waters provide much needed water resources in particular in arid and semi-arid regions where precipitation events can be very unevenly distributed throughout the year. Freshwater floods in particular play an important role in maintaining ecosystems in river corridors and are a key factor in maintaining floodplain biodiversity. Periodic flooding was essential to the well-being of ancient communities along the Tigris-Euphrates Rivers, the Nile River, the Indus River, the Ganges and the Yellow River, among others. The viability for hydrological based renewable sources of energy is higher in flood prone regions.
Computer modeling While flood modelling is a fairly recent practice, attempts to understand and manage the mechanisms at work in floodplains have been made for at least six millennia. The recent development in computational flood modelling has enabled engineers to step away from the tried and tested "hold or break" approach and its tendency to promote overly engineered structures. Various computational flood models have been developed in recent years either 1D models (flood levels measured in the channel) and 2D models (flood depth measured for the extent of the floodplain). HEC-RAS, the Hydraulic Engineering Centre model, is currently among the most popular if only because it is available for free. Other models such as TUFLOW combine 1D and 2D components to derive flood depth in the floodplain. So far the focus has been on mapping tidal and fluvial flood events but the 2007 flood events in the UK have shifted the emphasis onto the impact of surface water flooding.
D) Forest fires A wildfire is any uncontrolled fire in combustible vegetation that occurs in the countryside or a wilderness area. Other names such as brush fire, bushfire, forest fire, grass fire, hill fire, peat fire, vegetation fire, veldfire and wildland fire may be used to describe the same phenomenon depending on the type of vegetation being burned. A wildfire differs from other fires by its extensive size, the speed at which it can spread out from its original source, its potential to change direction unexpectedly, and its ability to jump gaps such as roads, rivers and fire breaks. Wildfires are characterized in terms of the cause of ignition, their physical properties such as speed of propagation, the combustible material present, and the effect of weather on the fire. Wildfires occur on every continent except Antarctica. Fossil records and human history contain accounts of wildfires, as wildfires can occur in periodic intervals.[5][6] Wildfires can cause extensive damage, both to property and human life, but they also have various beneficial effects on wilderness areas. Some plant species depend on the effects of fire for growth and reproduction, although large wildfires may also have negative ecological effects. Strategies of wildfire prevention, detection, and suppression have varied over the years, and international wildfire management experts encourage further development of technology and research. One of the more controversial techniques is controlled burning: permitting or even igniting smaller fires to minimize the amount of flammable material available for a potential wildfire. While some wildfires burn in remote forested regions, they can cause extensive destruction of homes and other property located in the wildland-urban interface: a zone of transition between developed areas and undeveloped wilderness. The name wildfire was once a synonym for Greek fire but now refers to any large or destructive conflagration. Wildfires differ from other fires in that they take place outdoors in areas of grassland, woodlands, bushland, scrubland, peatland, and other wooded areas that act as a source of fuel, or combustible material. Buildings may become involved if a wildfire spreads to adjacent communities. While the causes of wildfires vary and the outcomes are always unique, all wildfires can be characterized in terms of their physical properties, their fuel type, and the effect that weather has on the fire. Wildfire behavior and severity result from the combination of factors such as available fuels, physical setting, and weather. While wildfires can be large, uncontrolled disasters that burn through 0.4 to 400 square kilometers (100 to 100,000 acres) or more, they can also be as small as 0.0010 square kilometers (0.25 acres) or less. Although smaller events may be included in wildfire modeling, most do not earn press attention. This can be problematic because public fire policies, which relate to fires of all sizes, are influenced more by the way the media portrays catastrophic wildfires than by small fires.
Causes The four major natural causes of wildfire ignitions are lightning, volcanic eruption, sparks from rockfalls, and spontaneous combustion. The thousands of coal seam fires that are burning around the world, such as those in Centralia, Burning Mountain, and several coal-
sustained fires in China, can also flare up and ignite nearby flammable material. However, many wildfires are attributed to human sources such as arson, discarded cigarettes, sparks from equipment, and power line arcs (as detected by arc mapping). In societies experiencing shifting cultivation where land is cleared quickly and farmed until the soil loses fertility, slash and burn clearing is often considered the least expensive way to prepare land for future use. Forested areas cleared by logging encourage the dominance of flammable grasses, and abandoned logging roads overgrown by vegetation may act as fire corridors. Annual grassland fires in Southern Vietnam can be attributed in part to the destruction of forested areas by herbicides, explosives, and mechanical land clearing and burning operations during the Vietnam War. The most common cause of wildfires varies throughout the world. In the United States, Canada, and Northwest China, for example, lightning is the major source of ignition. In other parts of the world, human involvement is a major contributor. In Mexico, Central America, South America, Africa, Southeast Asia, Fiji, and New Zealand, wildfires can be attributed to human activities such as animal husbandry, agriculture, and land-conversion burning. Human carelessness is a major cause of wildfires in China and in the Mediterranean Basin. In Australia, the source of wildfires can be traced to both lightning strikes and human activities such as machinery sparks and cast-away cigarette butts. Fuel type The spread of wildfires varies based on the flammable material present and its vertical arrangement. For example, fuels uphill from a fire are more readily dried and warmed by the fire than those downhill, yet burning logs can roll downhill from the fire to ignite other fuels. Fuel arrangement and density is governed in part by topography, as land shape determines factors such as available sunlight and water for plant growth. Overall, fire types can be generally characterized by their fuels as follows: Ground fires are fed by subterranean roots, duff and other buried organic matter. This fuel type is especially susceptible to ignition due to spotting. Ground fires typically burn by smoldering, and can burn slowly for days to months, such as peat fires in Kalimantan and Eastern Sumatra, Indonesia, which resulted from a Riceland creation project that unintentionally drained and dried the peat.
Crawling or surface fires are fueled by low-lying vegetation such as leaf and timber litter, debris, grass, and low-lying shrubbery. Ladder fires consume material between low-level vegetation and tree canopies, such as small trees, downed logs, and vines. Kudzu, Old World climbing fern, and other invasive plants that scale trees may also encourage ladder fires. Crown, canopy, or aerial fires burn suspended material at the canopy level, such as tall trees, vines, and mosses. The ignition of a crown fire, termed crowning, is dependent on the density of the suspended material, canopy height, canopy continuity, and sufficient surface and ladder fires in order to reach the tree crowns. For example, ground-clearing fires lit by humans can spread into the Amazon rain forest, damaging ecosystems not particularly suited for heat or arid conditions.
Physical properties Wildfires occur when all of the necessary elements of a fire triangle come together in a wooded area: an ignition source is brought into contact with a combustible material such as vegetation, which is subjected to sufficient heat and has an adequate supply of oxygen from the ambient air. High moisture content usually prevents ignition and slows propagation, because higher temperatures are required to evaporate any water within the material and heat the material to its fire point. Dense forests usually provide more shade, resulting in lower ambient temperatures and greater humidity, and are therefore less susceptible to wildfires. Less dense material such as grasses and leaves are easier to ignite because they contain less water than denser material such as branches and trunks. Plants continuously lose water by evapotranspiration, but water loss is usually balanced by water absorbed from the soil, humidity, or rain. When this balance is not maintained, plants dry out and are therefore more flammable, often a consequence of droughts. A wildfire front is the portion sustaining continuous flaming combustion, where unburned material meets active flames, or the smoldering transition between unburned and burned material. As the front approaches, the fire heats both the surrounding air and woody material through convection and thermal radiation. First, wood is dried as water is vaporized at a temperature of 100 °C (212 °F). Next, the pyrolysis of wood at 230 °C (450 °F) releases flammable gases. Finally, wood can smolder at 380 °C (720 °F) or, when heated sufficiently, ignite at 590 °C (1,000 °F). Even before the flames of a wildfire arrive at a particular location, heat transfer from the wildfire front warms the air to 800 °C (1,470 °F), which preheats and dries flammable materials, causing materials to ignite faster and allowing the fire to spread faster. High-temperature and long-duration surface wildfires may encourage flashover or torching: the drying of tree canopies and their subsequent ignition from below. Wildfires have a rapid forward rate of spread (FROS) when burning through dense, uninterrupted fuels. They can move as fast as 10.8 kilometers per hour (6.7 mph) in forests and 22 kilometers per hour (14 mph) in grasslands. Wildfires can advance tangential to the main front to form a flanking front, or burn in the opposite direction of the main front by backing. They may also spread by jumping or spotting as winds and vertical convection columns carry firebrands (hot wood embers) and other burning materials through the air over roads, rivers, and other barriers that may otherwise act as firebreaks. Torching and fires in tree canopies encourage spotting, and dry ground fuels that surround a wildfire are especially vulnerable to ignition from firebrands. Spotting can create spot fires as hot embers and firebrands ignite fuels downwind from the fire. In Australian bushfires, spot fires are known to occur as far as 10 kilometers (6 mi) from the fire front. Especially large wildfires may affect air currents in their immediate vicinities by the stack effect: air rises as it is heated, and large wildfires create powerful updrafts that will draw in new, cooler air from surrounding areas in thermal columns. Great vertical differences in temperature and humidity encourage pyrocumulus clouds, strong winds, and fire whirls with the force of tornadoes at speeds of more than 80 kilometers per hour (50 mph). Rapid rates of spread, prolific crowning or spotting, the presence of fire whirls, and strong convection columns signify extreme conditions.
Effect of weather Heat waves, droughts, cyclical climate changes such as El Niño, and regional weather patterns such as high-pressure ridges can increase the risk and alter the behavior of wildfires dramatically. Years of precipitation followed by warm periods can encourage more widespread fires and longer fire seasons. Since the mid 1980s, earlier snowmelt and associated warming has also been associated with an increase in length and severity of the wildfire season in the Western United States. However, one individual element does not always cause an increase in wildfire activity. For example, wildfires will not occur during a drought unless accompanied by other factors, such as lightning (ignition source) and strong winds (mechanism for rapid spread). Fire intensity also increases during daytime hours. Burn rates of smoldering logs are up to five times greater during the day due to lower humidity, increased temperatures, and increased wind speeds. Sunlight warms the ground during the day which creates air currents that travel uphill. At night the land cools, creating air currents that travel downhill. Wildfires are fanned by these winds and often follow the air currents over hills and through valleys. Fires in Europe occur frequently during the hours of 12:00 p.m. and 2:00 p.m. Wildfire suppression operations in the United States revolve around a 24-hour fire day that begins at 10:00 a.m. due to the predictable increase in intensity resulting from the daytime warmth.
Plant adaptation Plants in wildfire-prone ecosystems often survive through adaptations to their local fire regime. Such adaptations include physical protection against heat, increased growth after a fire event, and flammable materials that encourage fire and may eliminate competition. For example, plants of the genus Eucalyptus contain flammable oils that encourage fire and hard sclerophyll leaves to resist heat and drought, ensuring their dominance over less fire-tolerant species. Dense bark, shedding lower branches, and high water content in external structures may also protect trees from rising temperatures. Fire-resistant seeds and reserve shoots that sprout after a fire encourage species preservation, as embodied by pioneer species. Smoke, charred wood, and heat can stimulate the germination of seeds in a process called serotiny. Exposure to smoke from burning plants promotes germination in other types of plants by inducing the production of the orange butenolide. Grasslands in Western Sabah, Malaysian pine forests, and Indonesian Casuarina forests are believed to have resulted from previous periods of fire. Chamise deadwood litter is low in water content and flammable, and the shrub quickly sprouts after a fire. Sequoia rely on periodic fires to reduce competition, release seeds from their cones, and clear the soil and canopy for new growth. Caribbean Pine in Bahamian pineyards have adapted to and rely on low-intensity, surface fires for survival and growth. An optimum fire frequency for growth is every 3 to 10 years. Too frequent fires favor herbaceous plants, and infrequent fires favor species typical of Bahamian dry forests.
Prevention Wildfire prevention refers to the preemptive methods of reducing the risk of fires as well as lessening its severity and spread. Effective prevention techniques allow supervising agencies to manage air quality, maintain ecological balances, protect resources, and to limit the effects of future uncontrolled fires. North American firefighting policies may permit
naturally caused fires to burn to maintain their ecological role, so long as the risks of escape into high-value areas are mitigated. However, prevention policies must consider the role that humans play in wildfires, since, for example, 95% of forest fires in Europe are related to human involvement. Sources of human-caused fire may include arson, accidental ignition, or the uncontrolled use of fire in land-clearing and agriculture such as the slash-and-burn farming in Southeast Asia. In the mid-19th century, explorers from the HMS Beagle observed Australian Aborigines using fire for ground clearing, hunting, and regeneration of plant food in a method later named fire-stick farming. Such careful use of fire has been employed for centuries in the lands protected by Kakadu National Park to encourage biodiversity. In 1937, U.S. President Franklin D. Roosevelt initiated a nationwide fire prevention campaign, highlighting the role of human carelessness in forest fires. Later posters of the program featured Uncle Sam, leaders of the Axis powers of World War II, characters from the Disney movie Bambi, and the official mascot of the U.S. Forest Service, Smokey Bear. Wildfires are caused by a combination of natural factors such as topography, fuels, and weather. Other than reducing human infractions, only fuels may be altered to affect future fire risk and behavior. Wildfire prevention programs around the world may employ techniques such as wildland fire use and prescribed or controlled burns. Wildland fire use refers to any fire of natural causes that is monitored but allowed to burn. Controlled burns are fires ignited by government agencies under less dangerous weather conditions. Vegetation may be burned periodically to maintain high species diversity, and frequent burning of surface fuels limits fuel accumulation, thereby reducing the risk of crown fires. Using strategic cuts of trees, fuels may also be removed by handcrews in order to clean and clear the forest, prevent fuel build-up, and create access into forested areas. Chain saws and large equipment can be used to thin out ladder fuels and shred trees and vegetation to a mulch. Multiple fuel treatments are often needed to influence future fire risks, and wildfire models may be used to predict and compare the benefits of different fuel treatments on future wildfire spread. However, controlled burns are reportedly "the most effective treatment for reducing a fire’s rate of spread, fireline intensity, flame length, and heat per unit of area" according to Jan Van Wagtendonk, a biologist at the Yellowstone Field Station. Additionally, while fuel treatments are typically limited to smaller areas, effective fire management requires the administration of fuels across large landscapes in order to reduce future fire size and severity. Building codes in fire-prone areas typically require that structures be built of flame-resistant materials and a defensible space be maintained by clearing flammable materials within a prescribed distance from the structure. Communities in the Philippines also maintain fire lines 5 to 10 meters (16 to 33 ft) wide between the forest and their village, and patrol these lines during summer months or seasons of dry weather. Fuel buildup can result in costly, devastating fires as new homes, ranches, and other development are built adjacent to wilderness areas. Continued growth in fire-prone areas and rebuilding structures destroyed by fires has been met with criticism. However, the population growth along the wildland-urban interface discourages the use of current fuel management techniques. Smoke is an irritant and attempts to thin out the fuel load is met with opposition due to desirability of forested areas, in addition to other wilderness goals such as endangered species protection and habitat preservation. The ecological benefits of fire are often overridden by the economic and safety benefits of
protecting structures and human life. For example, while fuel treatments decrease the risk of crown fires, these techniques destroy the habitats of various plant and animal species. Additionally, government policies that cover the wilderness usually differ from local and state policies that govern urban lands.
Detection Fast and effective detection is a key factor in wildfire fighting. Early detection efforts were focused on early response, accurate results in both daytime and nighttime, and the ability to prioritize fire danger. Fire lookout towers were used in the United States in the early 20th century and fires were reported using telephones, carrier pigeons, and heliographs. Aerial and land photography using instant cameras were used in the 1950s until infrared scanning was developed for fire detection in the 1960s. However, information analysis and delivery was often delayed by limitations in communication technology. Early satellitederived fire analyses were hand-drawn on maps at a remote site and sent via overnight mail to the fire manager. During the Yellowstone fires of 1988, a data station was established in West Yellowstone, permitting the delivery of satellite-based fire information in approximately four hours. Currently, public hotlines, fire lookouts in towers, and ground and aerial patrols can be used as a means of early detection of forest fires. However, accurate human observation may be limited by operator fatigue, time of day, time of year, and geographic location. Electronic systems have gained popularity in recent years as a possible resolution to human operator error. These systems may be semi- or fully-automated and employ systems based on the risk area and degree of human presence, as suggested by GIS data analyses. An integrated approach of multiple systems can be used to merge satellite data, aerial imagery, and personnel position via Global Positioning System (GPS) into a collective whole for near-realtime use by wireless Incident Command Centers. A small, high risk area that features thick vegetation, a strong human presence, or is close to a critical urban area can be monitored using a local sensor network. Detection systems may include wireless sensor networks that act as automated weather systems: detecting temperature, humidity, and smoke. These may be battery-powered, solar-powered, or tree-rechargeable: able to recharge their battery systems using the small electrical currents in plant material. Larger, medium-risk areas can be monitored by scanning towers that incorporate fixed cameras and sensors to detect smoke or additional factors such as the infrared signature of carbon dioxide produced by fires. Additional capabilities such as night vision, brightness detection, and color change detection may also be incorporated into sensor arrays. Satellite and aerial monitoring can provide a wider view and may be sufficient to monitor very large, low risk areas. These more sophisticated systems employ GPS and aircraft-mounted infrared or high-resolution visible cameras to identify and target wildfires. Satellite-mounted sensors such as Envisat's Advanced Along Track Scanning Radiometer and European Remote-Sensing Satellite's Along-Track Scanning Radiometer can measure infrared radiation emitted by fires, identifying hot spots greater than 39 °C (102 °F). The National Oceanic and Atmospheric Administration's Hazard Mapping System combines remote-sensing data from satellite sources such as Geostationary Operational Environmental Satellite (GOES), Moderate-Resolution Imaging Spectroradiometer (MODIS), and Advanced Very High Resolution Radiometer (AVHRR) for detection of fire and smoke plume
locations. However, satellite detection is prone to offset errors, anywhere from 2 to 3 kilometers (1 to 2 mi) for MODIS and AVHRR data and up to 12 kilometers (7.5 mi) for GOES data. Satellites in geostationary orbits may become disabled, and satellites in polar orbits are often limited by their short window of observation time. Cloud cover and image resolution and may also limit the effectiveness of satellite imagery.
Suppression Wildfire suppression depends on the technologies available in the area in which the wildfire occurs. In less developed nations such as Thailand, the techniques used can be as simple as throwing sand or beating the fire with sticks or palm fronds. In more advanced nations, the suppression methods vary due to increased technological capacity. Silver iodide can be used to encourage snow fall, while fire retardants and water can be dropped onto fires by unmanned aerial vehicles, planes, and helicopters. Complete fire suppression is no longer an expectation, but the majority of wildfires are often extinguished before they grow out of control. While more than 99% of the 10,000 new wildfires each year are contained, escaped wildfires can cause extensive damage. Worldwide damage from wildfires is in the billions of euros annually. Wildfires in Canada and the US burn an average of 54,500 square kilometers (13,000,000 acres) per year. Above all, fighting wildfires can become deadly. A wildfire's burning front may also change direction unexpectedly and jump across fire breaks. Intense heat and smoke can lead to disorientation and loss of appreciation of the direction of the fire, which can make fires particularly dangerous. For example, during the 1949 Mann Gulch fire in Montana, USA, thirteen smokejumpers died when they lost their communication links, became disorientated, and were overtaken by the fire.[168] In the Australian February 2009 Victorian bushfires, at least 173 people died and over 2,029 homes and 3,500 structures were lost when they became engulfed by wildfire.[169]
Modeling Wildfire modeling is concerned with numerical simulation of wildfires in order to comprehend and predict fire behavior. Wildfire modeling can ultimately aid wildfire suppression, increase the safety of firefighters and the public, and minimize damage. Using computational science, wildfire modeling involves the statistical analysis of past fire events to predict spotting risks and front behavior. Various wildfire propagation models have been proposed in the past, including simple ellipses and egg- and fan-shaped models. Early attempts to determine wildfire behavior assumed terrain and vegetation uniformity. However, the exact behavior of a wildfire's front is dependent on a variety of factors, including windspeed and slope steepness. Modern growth models utilize a combination of past ellipsoidal descriptions and Huygens' Principle to simulate fire growth as a continuously expanding polygon. Extreme value theory may also be used to predict the size of large wildfires. However, large fires that exceed suppression capabilities are often regarded as statistical outliers in standard analyses, even though fire policies are more influenced by catastrophic wildfires than by small fires.
Fig. Fire propagation model E) Desert locust Plagues of the desert locust (Schistocerca gregaria) have threatened agricultural production in Africa, the Middle East, and Asia for centuries. The livelihood of at least onetenth of the world’s human population can be affected by this voracious insect. The desert locust is potentially the most dangerous of the locust pests because of the ability of swarms to fly rapidly across great distances. It has two to five generations per year. The northern highlands of Ethiopia (Tigray) and Eritrea slow the movements of desert locusts to the breeding areas of the Red Sea coast. Potential desert locust plagues originating in east Africa can be prevented if action is taken during or before localized outbreaks in Eritrea and Sudan (Jahn 1993). The 2004 desert locust outbreak has caused significant crop losses in West Africa and had a negative impact on food security in the region. While the desert locust alone is not responsible for famines, it can be an important contributing factor.
Desert locust ecology The desert locust lives a solitary life until it rains. Rain causes vegetation growth and allows the female to lay eggs in the sandy soil. The new vegetation provides food for the newly-hatched locusts and provides them with shelter as they develop into winged adults.
Fig. Solitary (top) and gregarious (bottom) desert locust nymphs
When vegetation is distributed in such a way that the nymphs, usually called hoppers, have to congregate to feed, and there has been sufficient rain for most eggs to hatch, the close physical contact causes the insects' hind legs to bump against one another. This stimulus triggers a cascade of metabolic and behavioral changes that cause the insects to transform from the solitary form to the gregarious form. When the hoppers become gregarious, they change from green-coloured to yellow and black, and the adults change from brown to red (immature) or yellow (mature). Their bodies become shorter, and they give off a pheromone that causes them to be attracted to each other, enhancing hopper band and subsequently swarm formation. Interestingly, the nymphal pheromone is different from the adult one. When exposed to the adult pheromone, hoppers become confused and disoriented, because they can apparently no longer "smell" each other, though the visual and tactile stimuli remain. After a few days, the hopper bands disintegrate and those that escape predation become solitary again. It is possible that this effect could aid locust control in the future. During quiet periods, called recessions, desert locusts are confined to a 16-millionsquare-kilometer belt that extends from Mauritania through the Sahara Desert in northern Africa, across the Arabian Peninsula, and into northwest India. Under optimal ecological and climatic conditions, several successive generations can occur, causing swarms to form and invade countries on all sides of the recession area, as far north as Spain and Russia, as far south as Nigeria and Kenya, and as far east as India and southwest Asia. As many as 60 countries can be affected within an area of 32 million square kilometers, or approximately 20 percent of the Earth's land surface. Locust swarms fly with the wind at roughly the speed of the wind. They can cover from 100 to 200 kilometers in a day, and will fly up to about 2,000 meters above sea level (thereafter, it becomes too cold). Therefore, swarms cannot cross tall mountain ranges such as the Atlas Mountains, the Hindu Kush or the Himalayas. They will not venture into the rain forests of Africa nor into central Europe. However, locust adults and swarms regularly cross the Red Sea between Africa and the Arabian Peninsula, and are even reported to have crossed the Atlantic Ocean from Africa to the Caribbean in ten days during the 1987-89 plague. A single swarm can cover up to 1200 square kilometers and can contain between 40 and 80 million locusts per square kilometer. The locust can live between three to six months, and there is a ten to sixteenfold increase in locust numbers from one generation to the next.
Crop loss Desert locusts can consume the approximate equivalent of their body mass each day (2 g) in green vegetation: leaves, flowers, bark, stems, fruit, and seeds. Nearly all crops, and noncrop plants, are at risk, including pearl millet, rice, maize, sorghum, sugarcane, barley, cotton, fruit trees, date palm, vegetables, rangeland grasses, acacia, pines, and banana. What is more, locust droppings are toxic, and spoil any stored food that is left uneaten. Crop loss from locusts was noted in the Bible and Qur'an; these insects have been documented as contributing to the severity of a number of Ethiopian famines. During the twentieth century, desert locust plagues occurred in 1926-1934, 1940-1948, 1949-1963, 1967-1969, 1987-1989 and 2003-2005. The significant crop loss caused by swarming desert locusts exacerbates problems of food shortage, and is a threat to food security.
Control Early warning and preventive control is the strategy adopted by locust-affected countries in Africa and Asia to try to stop locust plagues from developing and spreading. FAO's Desert Locust Information Service (DLIS) in Rome, Italy monitors the weather, ecological conditions and the locust situation on a daily basis. DLIS receives results of survey and control operations carried out by national teams in affected countries, and combines this information with satellite data such as MODIS, rainfall estimates and seasonal temperature and rainfall predictions to assess the current situation and forecast the timing, scale and location of breeding and migration up to six weeks in advance. The situation assessments and forecasts are published in monthly locust bulletins that date back to the 1970s. These are supplemented by warnings and alerts to affected countries and the international community. Those since the 1990s are available on the FAO Locust Watch web site [www.fao.org/ag/locusts]. FAO also provides information and training to affected countries and coordinates funding from donor agencies in case of major upsurges and plagues. The desert locust is a difficult pest to control, and control measures are further compounded by the large and often remote areas (16-30 million km²) where locusts can be found. Undeveloped basic infrastructure in some affected countries, limited resources for locust monitoring and control, and political turmoil within and between affected countries further reduce the capacity of a country to undertake the necessary monitoring and control activities. At present, the primary method of controlling desert locust infestations is with insecticides applied in small concentrated doses by vehicle-mounted and aerial sprayers at ultra-low volume (ULV) rates of application. The insecticide is acquired by the insect directly or via secondary pickup (i.e. walking over or eating the residue on a plant). Control is undertaken by government agencies in locust-affected countries or by specialised organisations such as the Desert Locust Control Organisation for East Africa (DLCO-EA). Natural enemies such as predatory and parasitic wasps and flies, predatory beetle larvae, birds, and reptiles may have limited effects on desert locusts because they can be easily overwhelmed by the sheer magnitude of most swarms and hopper bands. On the other hand, they may be effective in keeping solitary populations in check. Farmers often try mechanical means of killing locusts, such as digging trenches and burying hopper bands, but this is very labor intensive and is difficult to undertake when large infestations are scattered over a wide area. Farmers also try to scare locust swarms away from their fields by making noise, burning tires or other methods. This tends to shift the problem to neighbouring farms, and locust swarms can easily reinfest previous fields.
Biopesticides Biopesticides include fungi, bacteria, neem extract and pheromones. The effectiveness of many biopesticides equals that of conventional chemical pesticides, but there are two distinct differences. Biopesticides in general take longer to kill insects, plant diseases, or weeds, usually between 2 and 10 days. There are two types of biopesticides - biochemical and microbial. Biochemical pesticides are similar to naturally occurring chemicals and are nontoxic, such as insect
pheromones used to locate mates, while microbial biopesticides like Green Muscle come from bacteria, fungi, algae or viruses that either occur naturally or are genetically altered. Entomopathogenic fungi generally suppress pests by mycosis: causing a disease that is specific to the insect. A biological control product has been under development since the late nineties. It is based on a naturally occurring entomopathogenic fungus (i.e. insects-infecting fungus) , Metarhizium acridum. Species of Metarhizium are widespread throughout the world, infecting many groups of insects, but show a low risk to humans, other mammals and birds. The species M. acridum has specialised on short-horned grasshoppers, to which group locusts belong, and has therefore been chosen as the active ingredient of the product. The product is available in Africa under the name Green Muscle and in Australia as Green Guard. It is applied in the same way as chemical insecticides, but does not kill as quickly. At recommended doses, the fungus can take up two weeks to kill up to 90% of the locusts. For that reason, it is recommended for use mainly against hoppers, the wingless early stages of locusts. These are mostly found in the desert, far from cropping areas, where the delay in death does not result in damage. The advantage of the product is that it affects only grasshoppers and locusts, which makes it much safer than chemical insecticides. Specifically, it allows the natural enemies of locusts and grasshoppers to continue their beneficial work. These include birds, parasitoid and predatory wasps, parasitoid flies and certain species of beetles. Though natural enemies cannot prevent plagues, they can limit the frequency of outbreaks and contribute to their control. Biopesticides are also safer to use in environmentally sensitive areas such as national parks or near rivers and other water bodies. Green Muscle was developed under the LUBILOSA Programme, which was initiated in 1989 in response to environmental concerns over the heavy use of chemical insecticides to control locusts and grasshoppers during the 1987-89 plague. The project focused on the use of beneficial disease-causing microorganisms (pathogens) as biological control agents for grasshoppers and locusts. These insects were considered to be too mobile and to reproduce too fast to be readily controlled by classical biological control. Pathogens have the advantage that many can be produced in artificial culture in large quantities and be used with ordinary spraying equipment. Entomopathogenic fungi were traditionally seen as needing humid conditions to work well. However, the LUBILOSA Programme found a way to avoid this by spraying fungal spores in an oil formulation. Even under desert conditions, Green Muscle can be used to kill locusts and other Acridid pests, such as the Senegalese grasshopper. During recent trials in Algeria and Mauritania (2005 and 2006), various natural enemies, but especially birds, were abundant enough to eliminate treated hopper bands in about a week, because the diseased hoppers became sluggish and easy to catch.
Desert locusts in culture Owing to the destructive habits of locusts, they have been a representation of famine in many Middle Eastern cultures. This theme commonly occurs, such as in the movies The Mummy and The Bible.
F) Cyclone In meteorology, a cyclone is an area of closed, circular fluid motion rotating in the same direction as the Earth. This is usually characterized by inward spiraling winds that rotate counter clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere of the Earth. Most large-scale cyclonic circulations are centered on areas of low atmospheric pressure. The largest low-pressure systems are cold-core polar cyclones and extratropical cyclones which lie on the synoptic scale. Warm-core cyclones such as tropical cyclones, mesocyclones, and polar lows lie within the smaller mesoscale. Subtropical cyclones are of intermediate size. Upper level cyclones can exist without the presence of a surface low, and can pinch off from the base of the Tropical Upper Tropospheric Trough during the summer months in the Northern Hemisphere. Cyclones have also been seen on other planets outside of the Earth, such as Mars and Neptune. Cyclogenesis describes the process of cyclone formation and intensification. Extratropical cyclones form as waves in large regions of enhanced midlatitude temperature contrasts called baroclinic zones. These zones contract to form weather fronts as the cyclonic circulation closes and intensifies. Later in their life cycle, cyclones occlude as cold core systems. A cyclone's track is guided over the course of its 2 to 6 day life cycle by the steering flow of the cancer or subtropical jet stream. Weather fronts separate two masses of air of different densities and are associated with the most prominent meteorological phenomena. Air masses separated by a front may differ in temperature or humidity. Strong cold fronts typically feature narrow bands of thunderstorms and severe weather, and may on occasion be preceded by squall lines or dry lines. They form west of the circulation center and generally move from west to east. Warm fronts form east of the cyclone center and are usually preceded by stratiform precipitation and fog. They move pole ward ahead of the cyclone path. Occluded fronts form late in the cyclone life cycle near the center of the cyclone and often wrap around the storm center. Tropical cyclogenesis describes the process of development of tropical cyclones. Tropical cyclones form due to latent heat driven by significant thunderstorm activity, and are warm core. Cyclones can transition between extratropical, subtropical, and tropical phases under the right conditions. Mesocyclones form as warm core cyclones over land, and can lead to tornado formation. Waterspouts can also form from mesocyclones, but more often develop from environments of high instability and low vertical wind shear.
Structure There are a number of structural characteristics common to all cyclones. As they are low pressure areas, their center is the area of lowest atmospheric pressure in the region, often known in mature tropical cyclones as the eye. Near the center, the pressure gradient force (from the pressure in the center of the cyclone compared to the pressure outside the cyclone) and the Coriolis force must be in an approximate balance, or the cyclone would collapse on itself as a result of the difference in pressure. The wind flow around a large cyclone is counterclockwise in the northern hemisphere and clockwise in the southern hemisphere as a result of the Coriolis Effect. (An anticyclone, on the other hand, rotates clockwise in the northern hemisphere, and counterclockwise in the southern hemisphere.)
Cyclogenesis and Tropical cyclogenesis Cyclogenesis is the development or strengthening of cyclonic circulation in the atmosphere (a low pressure area). Cyclogenesis is an umbrella term for several different processes, all of which result in the development of some sort of cyclone. It can occur at various scales, from the micro scale to the synoptic scale. Extra tropical cyclones form as waves along weather fronts before occluding later in their life cycle as cold core cyclones. Tropical cyclones form due to latent heat driven by significant thunderstorm activity, and are warm core. Mesocyclones form as warm core cyclones over land, and can lead to tornado formation. Waterspouts can also form from mesocyclones, but more often develop from environments of high instability and low vertical wind shear. Cyclogenesis is the opposite of cyclolysis, and has an anticyclonic (high pressure system) equivalent which deals with the formation of high pressure areas—Anticyclogenesis. The surface low has a variety of ways of forming. Topography can force a surface low when dense low-level high pressure system ridges in east of a north-south mountain barrier. Mesoscale convective systems can spawn surface lows which are initially warm core. The disturbance can grow into a wave-like formation along the front and the low will be positioned at the crest. Around the low, flow will become cyclonic, by definition. This rotational flow will push polar air equatorward west of the low via its trailing cold front, and warmer air with push pole ward low via the warm front. Usually the cold front will move at a quicker pace than the warm front and “catch up” with it due to the slow erosion of higher density airmass located out ahead of the cyclone and the higher density airmass sweeping in behind the cyclone, usually resulting in a narrowing warm sector. At this point an occluded front forms where the warm air mass is pushed upwards into a trough of warm air aloft, which is also known as a trowal. Tropical cyclogenesis is the technical term describing the development and strengthening of a tropical cyclone in the atmosphere. The mechanisms through which tropical cyclogenesis occurs are distinctly different from those through which mid-latitude cyclogenesis occurs. Tropical cyclogenesis involves the development of a warm-core cyclone, due to significant convection in a favorable atmospheric environment. There are six main requirements for tropical cyclogenesis: sufficiently warm sea surface temperatures, atmospheric instability, high humidity in the lower to middle levels of the troposphere, enough Coriolis force to develop a low pressure center, a preexisting low level focus or disturbance, and low vertical wind shear. An average of 86 tropical cyclones of tropical storm intensity form annually worldwide, with 47 reaching hurricane/typhoon strength, and 20 becoming intense tropical cyclones (at least Category 3 intensity on the Saffir-Simpson Hurricane Scale).
Surface-based types There are six main types of cyclones: Polar cyclones, Polar lows, Extratropical cyclones, Subtropical cyclones, Tropical cyclones, and Mesocyclones
Polar cyclone A polar, sub-polar, or Arctic cyclone (also known as a polar vortex) is a vast area of low pressure which strengthens in the winter and weakens in the summer. A polar cyclone is
a low pressure weather system, usually spanning 1,000 kilometers (620 mi) to 2,000 kilometers (1,200 mi), in which the air circulates in a counterclockwise direction in the northern hemisphere, and a clockwise direction in the southern hemisphere. In the Northern Hemisphere, the polar cyclone has two centers on average. One center lies near Baffin Island and the other over northeast Siberia. In the southern hemisphere, it tends to be located near the edge of the Ross Ice Shelf near 160 west longitude. When the polar vortex is strong, westerly flow descends to the Earth's surface. When the polar cyclone is weak, significant cold outbreaks occur.
Polar low A polar low is a small-scale, short-lived atmospheric low pressure system (depression) that is found over the ocean areas poleward of the main polar front in both the Northern and Southern Hemispheres. The systems usually have a horizontal length scale of less than 1,000 kilometres (620 mi) and exist for no more than a couple of days. They are part of the larger class of mesoscale weather systems. Polar lows can be difficult to detect using conventional weather reports and are a hazard to high-latitude operations, such as shipping and gas and oil platforms. Polar lows have been referred to by many other terms, such as polar mesoscale vortex, Arctic hurricane, Arctic low, and cold air depression. Today the term is usually reserved for the more vigorous systems that have near-surface winds of at least 17 m/s.
Extratropical A fictitious synoptic chart of an extra tropical cyclone affecting the UK and Ireland. The blue arrows between isobars indicate the direction of the wind, while the "L" symbol denotes the centre of the "low". Note the occluded, cold and warm frontal boundaries. An extratropical cyclone is a synoptic scale low pressure weather system that has neither tropical nor polar characteristics, being connected with fronts and horizontal gradients in temperature and dew point otherwise known as "baroclinic zones". The descriptor "extratropical" refers to the fact that this type of cyclone generally occurs outside of the tropics, in the middle latitudes of the planet. These systems may also be described as "mid-latitude cyclones" due to their area of formation, or "post-tropical cyclones" where extra tropical transition has occurred, and are often described as "depressions" or "lows" by weather forecasters and the general public. These are the everyday phenomena which along with anti-cyclones, drive the weather over much of the Earth. Although extratropical cyclones are almost always classified as baroclinic since they form along zones of temperature and dewpoint gradient within the westerlies, they can sometimes become barotropic late in their life cycle when the temperature distribution around the cyclone becomes fairly uniform with radius. An extratropical cyclone can transform into a subtropical storm, and from there into a tropical cyclone, if it dwells over warm waters and develops central convection, which warms its core.
Subtropical A subtropical cyclone is a weather system that has some characteristics of a tropical cyclone and some characteristics of an extratropical cyclone. They can form between the equator and the 50th parallel. As early as the 1950s, meteorologists were unclear whether they should be characterized as tropical cyclones or extratropical cyclones, and used terms such as quasi-tropical and semi-tropical to describe the cyclone hybrids. By 1972, the National Hurricane Center officially recognized this cyclone category. Subtropical cyclones began to receive names off the official tropical cyclone list in the Atlantic Basin in 2002. They have broad wind patterns with maximum sustained winds located farther from the center than typical tropical cyclones, and exist in areas of weak to moderate temperature gradient. Since they form from initially extratropical cyclones which have colder temperatures aloft than normally found in the tropics, the sea surface temperatures required for their formation are lower than the tropical cyclone threshold by three degrees Celsius, or five degrees Fahrenheit, lying around 23 degrees Celsius. This means that subtropical cyclones are more likely to form outside the traditional bounds of the hurricane season. Although subtropical storms rarely have hurricane-force winds, they may become tropical in nature as their cores warm.
Tropical A tropical cyclone is a storm system characterized by a low pressure center and numerous thunderstorms that produce strong winds and flooding rain. A tropical cyclone feeds on heat released when moist air rises, resulting in condensation of water vapour contained in the moist air. They are fueled by a different heat mechanism than other cyclonic windstorms such as nor'easters, European windstorms, and polar lows, leading to their classification as "warm core" storm systems. The term "tropical" refers to both the geographic origin of these systems, which form almost exclusively in tropical regions of the globe, and their formation in Maritime Tropical air masses. The term "cyclone" refers to such storms' cyclonic nature, with counterclockwise rotation in the Northern Hemisphere and clockwise rotation in the Southern Hemisphere. Depending on their location and strength, tropical cyclones are referred to by other names, such as hurricane, typhoon, tropical storm, cyclonic storm, tropical depression, or simply as a cyclone. Generally speaking, a tropical cyclone is referred to as a hurricane (from the name of the ancient Central American deity of wind, Hurricane) in the Atlantic basin, and a Cyclone in the Pacific. While tropical cyclones can produce extremely powerful winds and torrential rain, they are also able to produce high waves and damaging storm surge. They develop over large bodies of warm water, and lose their strength if they move over land. This is the reason coastal regions can receive significant damage from a tropical cyclone, while inland regions are relatively safe from receiving strong winds. Heavy rains, however, can produce significant flooding inland, and storm surges can produce extensive coastal flooding up to 40 kilometers (25 mi) from the coastline. Although their effects on human populations can be devastating, tropical cyclones can also relieve drought conditions. They also carry heat and energy away from the tropics and transport it toward temperate latitudes, which makes them
an important part of the global atmospheric circulation mechanism. As a result, tropical cyclones help to maintain equilibrium in the Earth's troposphere. Many tropical cyclones develop when the atmospheric conditions around a weak disturbance in the atmosphere are favorable. Others form when other types of cyclones acquire tropical characteristics. Tropical systems are then moved by steering winds in the troposphere; if the conditions remain favorable, the tropical disturbance intensifies, and can even develop an eye. On the other end of the spectrum, if the conditions around the system deteriorate or the tropical cyclone makes landfall, the system weakens and eventually dissipates. A tropical cyclone can become extratropical as it moves toward higher latitudes if its energy source changes from heat released by condensation to differences in temperature between air masses; From an operational standpoint, a tropical cyclone is usually not considered to become subtropical during its extratropical transition.
Mesocyclone A mesocyclone is a vortex of air, approximately 2.0 kilometres (1.2 mi) to 10 kilometres (6.2 mi) in diameter (the mesoscale of meteorology), within a convective storm. Air rises and rotates around a vertical axis, usually in the same direction as low pressure systems in both northern and southern hemisphere. They are most often cyclonic, that is, associated with a localized low-pressure region within a severe thunderstorm. Such storms can feature strong surface winds and severe hail. Mesocyclones often occur together with updrafts in supercells, where tornadoes may form. About 1700 mesocyclones form annually across the United States, but only half produce tornadoes. Cyclones are not unique to Earth. Cyclonic storms are common on Jovian planets, like the Small Dark Spot on Neptune. Also known as the Wizard's Eye, it is about one third the diameter of the Great Dark Spot. It received the name "Wizard's Eye" because it looks like an eye. This appearance is caused by a white cloud in the middle of the Wizard's Eye. Mars has also exhibited cyclonic storms. Jovian storms like the Great Red Spot are usually mistakenly named as giant hurricanes or cyclonic storms. However, this is inaccurate, as the Great Red Spot is, in fact, the inverse phenomenon, an anticyclone.
Upper level types TUTT cell Under specific circumstances, upper cold lows can break off from the base of the Tropical Upper Tropospheric Trough (TUTT), which is located mid-ocean in the Northern Hemisphere during the summer months. These upper tropospheric cyclonic vortices, also known as TUTT cells or TUTT lows, usually move slowly from east-northeast to westsouthwest, and generally do not extend below 20,000 feet in altitude. A weak inverted surface trough within the trade wind is generally found underneath them, and they may also be associated with broad areas of high-level clouds. Downward development results in an increase of cumulus clouds and the appearance of a surface vortex. In rare cases, they become warm-core, resulting in the vortex becoming a tropical cyclone. Upper cyclones and upper troughs which trail tropical cyclones can cause additional outflow channels and aid in their intensification process. Developing tropical disturbances can help create or deepen upper
troughs or upper lows in their wake due to the outflow jet emanating from the developing tropical disturbance/cyclone.
G) Fog Fog is a collection of water droplets or ice crystals suspended in the air at or near the Earth's surface. While fog is a type of a cloud, the term "fog" is typically distinguished from the more generic term "cloud" in that fog is low-lying, and the moisture in the fog is often generated locally (such as from a nearby body of water, like a lake or the ocean, or from nearby moist ground or marshes). Fog is distinguished from mist only by its density, as expressed in the resulting decrease in visibility: Fog reduces visibility to less than 1 km (5/8 statute mile), whereas mist reduces visibility to no less than 1 km (5/8 statute mile). For aviation purposes in the UK, a visibility of less than 2 km but greater than 999 m is considered to be mist if the relative humidity is 95% or greater - below 95% haze is reported. The foggiest place in the world is the Grand Banks off the island of Newfoundland, the meeting place of the cold Labrador Current from the north and the much warmer Gulf Stream from the south. Some of the foggiest land areas in the world include Argentia, Newfoundland and Labrador and Point Reyes, California, each with over 200 foggy days per year. Even in generally warmer southern Europe, thick fog and localized fog is often found in lowlands and valleys, such as the lower part of the Po Valley and the Arno and Tiber valleys, as well as on the Swiss plateau, especially in the Seeland area, in late autumn and winter. Other notably foggy areas include coastal Chile (in the south), coastal Namibia, and the Severnaya Zemlya islands. Seattle, Washington, USA, has many foggy days per year.
Characteristics Fog forms when the difference between temperature and dew point is generally less than 2.5 °C or 4 F. Fog begins to form when water vapor condenses into tiny liquid water droplets in the air. The main ways water vapor is added to the air are: wind convergence into areas of upward motion, precipitation or virga falling from above, daytime heating evaporating water from the surface of oceans, water bodies or wet land, transpiration from plants, cool or dry air moving over warmer water, and lifting air over mountains. Water vapor normally begins to condense on condensation nuclei such as dust, ice, and salt in order to form clouds. Fog, like its slightly elevated cousin stratus, is a stable cloud deck which tends to form when a cool, stable air mass is trapped underneath a warm air mass. Fog normally occurs at a relative humidity near 100%. This can be achieved by either adding moisture to the air or dropping the ambient air temperature. Fog can form at lower humidities, and fog can sometimes not form with relative humidity at 100%. A reading of 100% relative humidity means that the air can hold no additional moisture; the air will become supersaturated if additional moisture is added.
Fog can form suddenly, and can dissipate just as rapidly, depending what side of the dew point the temperature is on. This phenomenon is known as flash fog. Another common type of formation is associated with sea fog (also known as haar or fret). This is due to the peculiar effect of salt. Clouds of all types require minute hygroscopic particles upon which water vapor can condense. Over the ocean surface, the most common particles are salt from salt spray produced by breaking waves. Except in areas of storminess, the most common areas of breaking waves are located near coastlines; hence the greatest densities of airborne salt particles are there. Condensation on salt particles has been observed to occur at humidities as low as 70%, thus fog can occur even in relatively dry air in suitable locations such as the California coast. Typically, such lower humidity fog is preceded by a transparent mistiness along the coastline as condensation competes with evaporation, a phenomenon that is typically noticeable by beachgoers in the afternoon. Another recentlydiscovered source of condensation nuclei for coastal fog is kelp. Researchers have found that under stress (intense sunlight, strong evaporation, etc.), kelp release particles of iodine which in turn become nuclei for condensation of water vapor. Fog occasionally produces precipitation in the form of drizzle or very light snow. Drizzle occurs when the humidity of fog attains 100% and the minute cloud droplets begin to coalesce into larger droplets. This can occur when the fog layer is lifted and cooled sufficiently, or when it is forcibly compressed from above. Drizzle becomes freezing drizzle when the temperature at the surface drops below the freezing point. The thickness of fog is largely determined by the altitude of the inversion boundary, which in coastal or oceanic locales is also the top of the marine layer, above which the airmass is warmer and drier. The inversion boundary varies its altitude primarily in response to the weight of the air above it which is measured in terms of atmospheric pressure. The marine layer and any fogbank it may contain will be "squashed" when the pressure is high, and conversely, may expand upwards when the pressure above it is lowering.
Visibility hazard Shadows Shadows are cast through fog in three dimensions. The fog is dense enough to be illuminated by light that passes through gaps in a structure or tree, but thin enough to let a large quantity of that light pass through to illuminate points further on. As a result, object shadows appear as "beams" oriented in a direction parallel to the light source. These voluminous shadows are due to the same cause as crepuscular rays, which are the shadows of clouds, but in this case, they are the shadows of solid objects.
Types Fog can form in a number of ways, depending on how the cooling that caused the condensation occurred: Radiation fog is formed by the cooling of land after sunset by thermal radiation in calm conditions with clear sky. The cool ground produces condensation in the nearby air by heat conduction. In perfect calm the fog layer can be less than a meter deep but turbulence
can promote a thicker layer. Radiation fogs occur at night, and usually do not last long after sunrise. Radiation fog is common in autumn and early winter. Examples of this phenomenon include the Tule fog. Ground fog is fog that obscures less than 60% of the sky and does not extend to the base of any overhead clouds. However, the term is sometimes used to refer to radiation fog. Advection fog occurs when moist air passes over a cool surface by advection (wind) and is cooled. It is common as a warm front passes over an area with significant snowpack. It is most common at sea when tropical air encounters cooler waters, including areas of cold water upwelling, such as along the California coast. The advection of fog along the California coastline is propelled onto land by one of several processes. A cold front can push the marine layer coastward, an occurrence most typical in the spring or late fall. During the summer months, a low pressure trough produced by intense heating inland creates a strong pressure gradient, drawing in the dense marine layer. Also during the summer, strong high pressure aloft over the desert southwest, usually in connection with the summer monsoon, produces a south to southeasterly flow which can drive the offshore marine layer up the coastline; a phenomenon known as a "southerly surge", typically following a coastal heat spell. However, if the monsoonal flow is sufficiently turbulent, it might instead break up the marine layer and any fog it may contain. Moderate turbulence will typically transform a fog bank, lifting it and breaking it up into shallow convective clouds called stratocumulus. Sea smoke, also called steam fog or evaporation fog, is the most localized form and is created by cold air passing over warmer water or moist land. It often causes freezing fog, or sometimes hoar frost. Precipitation fog (or frontal fog) forms as precipitation falls into drier air below the cloud, the liquid droplets evaporate into water vapor. The water vapor cools and at the dewpoint it condenses and fog forms. Upslope fog or hill fog forms when winds blow air up a slope (called orographic lift), adiabatically cooling it as it rises, and causing the moisture in it to condense. This often causes freezing fog on mountaintops, where the cloud ceiling would not otherwise be low enough. Valley fog forms in mountain valleys, often during winter. It is the result of a temperature inversion caused by heavier cold air settling into a valley, with warmer air passing over the mountains above. It is essentially radiation fog confined by local topography, and can last for several days in calm conditions. In California's Central Valley, valley fog is often referred to as Tule fog. Freezing fog occurs when liquid fog droplets freeze to surfaces, forming white soft or hard rime. This is very common on mountain tops which are exposed to low clouds. It is equivalent to freezing rain, and essentially the same as the ice that forms inside a freezer which is not of the "frostless" or "frost-free" type. The term "freezing fog" may also refer to fog where water vapor is super-cooled filling the air with small ice crystals similar to very light snow. It seems to make the fog "tangible", as if one could "grab a handful". Frozen fog (also known as ice fog) is any kind of fog where the droplets have frozen into extremely tiny crystals of ice in midair. Generally this requires temperatures at or below
−35 °C (−30 °F), making it common only in and near the Arctic and Antarctic regions. It is most often seen in urban areas where it is created by the freezing of water vapor present in automobile exhaust and combustion products from heating and power generation. Urban ice fog can become extremely dense and will persist day and night until the temperature rises. Extremely small amounts of ice fog falling from the sky form a type of precipitation called ice crystals, often reported in Barrow, Alaska. Ice fog often leads to the visual phenomenon of light pillars. Artificial fog is artificially generated fog that is usually created by vaporizing a water and glycol-based or glycerin-based fluid. The fluid is injected into a heated block, and evaporates quickly. The resulting pressure forces the vapor out of the exit. Upon coming into contact with cool outside air the vapor condenses and appears as fog. Garua fog is a type of fog which happens to occur by the coast of Chile and Peru. The normal fog produced by the sea travels inland, but suddenly meets an area of hot air. This causes the water particles of fog to shrink by evaporation, producing a transparent mist. Garua fog is nearly invisible, yet it still forces drivers to use windshield wipers. Hail fog sometimes occurs in the vicinity of significant hail accumulations due to decreased temperature and increased moisture leading to saturation in a very shallow layer near the surface. It most often occurs when there is a warm, humid layer atop the hail and when wind is light. This ground fog tends to be localized but can be extremely dense and abrupt. It may form shortly after the hail falls; when the hail has had time to cool the air and as it absorbs heat when melting and evaporating. Ice fog or pogonip is rare, but can occur when temperatures are below -40 °C (-40 °F), when ice crystals freeze while suspended in the air, then stay.
Biological and human uses Redwood forests in California receive approximately 30 to 40 percent of their moisture from coastal fog. Change in climate patterns could result in relative drought in these areas.[27] Some coastal communities use fog nets to extract moisture from the atmosphere where groundwater pumping and rainwater collection are insufficient.
H) Storm A storm (from Proto-Germanic *sturmaz "noise, tumult") is any disturbed state of an astronomical body's atmosphere, especially affecting its surface, and strongly implying severe weather. It may be marked by strong wind, thunder and lightning (a thunderstorm), heavy precipitation, such as ice (ice storm), or wind transporting some substance through the atmosphere (as in a dust storm, snowstorm, hailstorm, etc.).
Formation
Storms are created when a center of low pressure develops, with a system of high pressure surrounding it. This combination of opposing forces can create winds and result in the formation of storm clouds, such as the cumulonimbus. Small, localized areas of low pressure can form from hot air rising off hot ground, resulting in smaller disturbances such as dust devils and whirlwinds.
Types There are many varieties and names for storms.
Ice Storm - Ice storms are one of the most dangerous forms of winter weather. When surface temperatures are below freezing, but a thick layer of above freezing air remains aloft above ground level, rain can fall into the freezing layer and freeze upon impact into a "glaze". In general, 8 millimeters (1/4 in) of accumulation is all that is required, especially in combination with breezy conditions, to start downing power lines as well as tree limbs. Ice storms also make unheated road surfaces too slick to drive upon. Ice storms can vary in time range from hours to days and can cripple both small towns and large urban centers alike. Blizzard - There are varying definitions for blizzards, both over time and by location. In general, a blizzard is accompanied by gale-force winds, heavy snow (accumulating at a rate of at least 5 centimeters (2 in) per hour), and very cold conditions (below approximately -10 degrees Celsius or 14 F). As of late, the temperature criterion has fallen out of the definition across the United States. Snowstorm - A heavy fall of snow accumulating at a rate of more than 5 centimeters (2 in) per hour that lasts several hours. Snow storms, especially ones with a high liquid equivalent and breezy conditions, can down tree limbs, cut off power, and paralyze travel over a large region. Ocean Storm - Storm conditions out at sea are defined as having sustained winds of 48 knots (55 mph or 90 km/h) or greater. Usually just referred to as a storm, these systems can sink vessels of all types and sizes. Firestorm - Firestorms are conflagrations which attain such intensity that they create and sustain their own wind systems. It is most commonly a natural phenomenon, created during some of the largest bushfires, forest fires, and wildfires. The Peshtigo Fire is one example of a firestorm. Firestorms can also be deliberate effects of targeted explosives such as occurred as a result of the aerial bombings of Dresden and Tokyo during World War II. Nuclear detonations almost invariably generate firestorms Dust devil - a small, localized updraft of rising air. Windstorm - A storm marked by high wind with little or no precipitation. Windstorm damage often opens the door for massive amounts of water and debris to cause further damage to a structure. European windstorms and derechos are two type of windstorms. Squall - sudden onset of wind increase of at least 16 knots (30 km/h) or greater sustained for at least one minute. Gale - An extratropical storm with sustained winds between 34-48 knots (39-55 mph or 63–90 km/h). Thunderstorm - A thunderstorm is a type of storm that generates lightning and the attendant thunder. It is normally accompanied by heavy precipitation. Thunderstorms
occur throughout the world, with the highest frequency in tropical rainforest regions where there are conditions of high humidity and temperature along with atmospheric instability. These storms occur when high levels of condensation form in a volume of unstable air that generates deep, rapid, upward motion in the atmosphere. The heat energy creates powerful rising air currents that swirl upwards to the tropopause. Cool descending air currents produce strong downdraughts below the storm. After the storm has spent its energy, the rising currents die away and downdraughts break up the cloud. Individual storm clouds can measure 2–10 km across. Tropical Cyclone - A tropical cyclone is a storm system with a closed circulation around a centre of low pressure, fueled by the heat released when moist air rises and condenses. The name underscores its origin in the tropics and their cyclonic nature. Tropical cyclones are distinguished from other cyclonic storms such as nor'easters and polar lows by the heat mechanism that fuels them, which makes them "warm core" storm systems.
Heavy storm brought by Typhoon Sanvu in Hong Kong. Sanvu was the first typhoon in 2005 that passed through the city. Tropical cyclones form in the oceans if the conditions in the area are favorable, and depending on their strength and location, there are various terms by which they are called, such as tropical depression, tropical storm, hurricane and typhoon.
Hailstorm - a type of storm that precipitates chunks of ice. Hailstorms usually occur during regular thunder storms. While most of the hail that precipitates from the clouds is fairly small and virtually harmless, there have been cases of hail greater than 2 inches diameter that caused much damage and injuries.
Tornado - A tornado is a violent, destructive wind storm occurring on land. Usually its appearance is that of a dark, funnel-shaped cyclone. Often tornadoes are preceded by a thunderstorm and a wall cloud. They are often called the most destructive of storms, and while they form all over the world, the interior of the United States is the most prone area, especially throughout Tornado Alley.
Classification A strict meteorological definition of a terrestrial storm is a wind measuring 10 or higher on the Beaufort scale, meaning a wind speed of 24.5 m/s (89 km/h, 55 mph) or more; however, popular usage is not so restrictive. Storms can last anywhere from 12 to 200 hours, depending on season and geography. The east and northeast storms are noted for the most frequent repeatability and duration, especially during the cold period.[8] Big terrestrial storms alter the oceanographic conditions that in turn may affect food abundance and distribution: strong currents, strong tides, increased siltation, change in water temperatures, overturn in the water column, etc.
Extraterrestrial storms Storms are not unique to Earth; other planetary bodies with a sufficient atmosphere (gas giants in particular) also undergo stormy weather. A famous example is the Great Red Spot on Jupiter. Though technically an anticyclone with greater than hurricane wind speeds, it is larger than the earth and has been raging for at least 340 years, having first been
observed by astronomer Galileo Galilei. Neptune also had its own lesser known Great Dark Spot.
I) Heat wave A heat wave is a prolonged period of excessively hot weather, which may be accompanied by high humidity. There is no universal definition of a heat wave, the term is relative to the usual weather in the area. Temperatures that people from a hotter climate consider normal can be termed a heat wave in a cooler area if they are outside the normal climate pattern for that area. The term is applied both to routine weather variations and to extraordinary spells of heat which may occur only once a century. Severe heat waves have caused catastrophic crop failures, thousands of deaths from hyperthermia, and widespread power outages due to increased use of air conditioning.
Definitions The definition recommended by the World Meteorological Organization is when the daily maximum temperature of more than five consecutive days exceeds the average maximum temperature by 5 Celsius degrees (9 Fahrenheit degrees), the normal period being 1961–1990. A formal, peer-reviewed definition from the Glossary of Meteorology is: A period of abnormally and uncomfortably hot and usually humid weather. To be a heat wave such a period should last at least one day, but conventionally it lasts from several days to several weeks. In 1900, A. T. Burrows more rigidly defined a “hot wave” as a spell of three or more days on each of which the maximum shade temperature reaches or exceeds 90 °F (32 °C). More realistically, the comfort criteria for any one region are dependent upon the normal conditions of that region. In the Netherlands, a heat wave is defined as period of at least 5 consecutive days in which the maximum temperature in De Bilt exceeds 25 °C (77 °F), provided that on at least 3 days in this period the maximum temperature in De Bilt exceeds 30 °C (86 °F). This definition of a heat wave is also used in Belgium and Luxembourg. In Denmark a heat wave is defined as a period of at least 3 consecutive days of which period the average maximum temperature across more than fifty percent of the country exceeds 28 °C. In the United States, definitions also vary by region; however, a heat wave is usually defined as a period of at least two or more days of excessively hot weather. In the Northeast, a heat wave is typically defined as three consecutive days where the temperature reaches or exceeds 90 °F (32 °C), but not always as this is ties in with humidity levels to determine a heat index threshold. The same does not apply to drier climates. A heat storm is a Californian
term for an extended heat wave. Heat storms occur when the temperature reaches 100 °F (38 °C) for three or more consecutive days over a wide area (tens of thousands of square miles). The National Weather Service issues heat advisories and excessive heat warnings when unusual periods of hot weather are expected. In Adelaide, Australia, a heat wave is defined as five consecutive days at or above 35 °C (95 °F), or three consecutive days at or over 40 °C (104 °F).
Incidence Heat waves often occur during the Dog Days of summer; indeed the French term canicule, denoting the general phenomenon of a heat wave, derives from the Italian canicula applied to the star Sirius, also known as the "Dog Star." Some regions of the globe are more susceptible to heat waves than others, typically inland desert, semi desert, and Mediterranean-type climates. According to climatologist David Jones the likelihood of heat waves occurring is expected to increase with global warming.
How they occur In the summer in warm climates, an area of high pressure with little or no rain or clouds, the air and ground easily heats to excess. A static high pressure area can impose a very persistent heat wave. The position of the jet stream allows air on one side to be considerably warmer than the other side. Heat waves are far more common and more severe on the warm side and at times an unusual position of the jet stream places unusual warmth in an unusual place for hot weather, and imposes a heat wave. El Niño and La Niña (opposite reaction to El Niño) can severely disrupt the positions of the jet streams. Large desert zones and dry areas are more likely to get extreme heat because there is rarely any high cloud cover with very low humidity. Winds from hot deserts typically push hot, dry air towards areas normally cooler than during a heat wave. During the summer an area that has no geographic features that might cool winds that originate in the hot deserts get little mitigation, especially near the summer solstice when long days and a high sun would create warm conditions even without the transport of hot air from other locations. Should such a hot air mass travel above a large body of water, as a sirocco of Saharan origin crossing the Mediterranean sea, it likely picks up much water vapor with a reduction in temperature but far greater humidity that makes the original desert air little less moderate as demonstrated in a high heat index. Heat waves can also come from air originating over tropical seas penetrating far into the middle latitudes heating further overland, as often occurs in the eastern United States and southeastern Canada. The heat island created by dense urbanization of large cities only exacerbate heat waves because of the weakness of night-time cooling. Hyperthermia, also known as heat stroke, becomes commonplace during periods of sustained high temperature and humidity. Sweating is absent from 84%–100% of those
affected. Older adults, very young children, and those who are sick or overweight are at a higher risk for heat-related illness. The chronically ill and elderly are often taking prescription medications (e.g., diuretics, anticholinergics, antipsychotics, and antihypertensives) that interfere with the body's ability to dissipate heat. Heat edema presents as a transient swelling of the hands, feet, and ankles and is generally secondary to increased aldosterone secretion, which enhances water retention. When combined with peripheral vasodilation and venous stasis, the excess fluid accumulates in the dependent areas of the extremities. The heat edema usually resolves within several days after the patient becomes acclimated to the warmer environment. No treatment is required, although wearing support stocking and elevating the affected legs with help minimize the edema. Heat rash, also known as prickly heat, is a maculopapular rash accompanied by acute inflammation and blocked sweat ducts. The sweat ducts may become dilated and may eventually rupture, producing small pruritic vesicles on an erythematous base. Heat rash affects areas of the body covered by tight clothing. If this continues for duration of time it can lead to the development of chronic dermatitis or a secondary bacterial infection. Prevention is the best therapy. It is also advised to wear loose-fitting clothing in the heat. However, once heat rash has developed, the initial treatment involves the application of chlorhexidine lotion to remove any desquamated skin. The associated itching may be treated with topical or systemic antihistamines. If infection occurs a regimen of antibiotics is required. Heat cramps are painful, often severe, involuntary spasms of the large muscle groups used in strenuous exercise. Heat cramps tend to occur after intense exertion. They usually develop in people performing heavy exercise while sweating profusely and replenishing fluid loss with non-electrolyte containing water. This is believed to lead to hyponatremia that induces cramping in stressed muscles. Rehydration with salt-containing fluids provides rapid relief. Patients with mild cramps can be given oral .2% salt solutions, while those with severe cramps require IV isotonic fluids. The many sport drinks on the market are a good source of electrolytes and are readily accessible. Heat syncope is related to heat exposure that produces orthostatic hypotension. This hypotension can precipitate a near-syncopal episode. Heat syncope is believed to result from intense sweating, which leads to dehydration, followed by peripheral vasodilation and reduced venous blood return in the face of decreased vasomotor control. Management of heat syncope consists of cooling and rehydration of the patient using oral rehydration therapy (sport drinks) or isotonic IV fluids. People who experience heat syncope should avoid standing in the heat for long periods of time. They should move to a cooler environment and lie down if they recognize the initial symptoms. Wearing support stockings and engaging in deep knee-bending movements can help promote venous blood return. Heat exhaustion is considered by experts to be the forerunner of heat stroke (hyperthermia). It may even resemble heat stroke, with the difference being that the neurologic function remains intact. Heat exhaustion is marked by excessive dehydration and electrolyte depletion. Symptoms may include headache, nausea, and vomiting, dizziness, tachycardia, malaise, and myalgia. Definitive therapy includes removing patients from the heat and replenishing their fluids. Most patients will require fluid replacement with IV isotonic fluids at first. The salt content is adjusted as necessary once the electrolyte levels are known. After discharge from the hospital, patients are instructed to rest, drink plenty of fluids
for 2–3 hours, and avoid the heat for several days. If this advice is not followed it may then lead to heat stroke. One public health measure taken during heat waves is the setting-up of airconditioned public cooling centers.
Mortality Heat waves are the most lethal type of weather phenomenon, overall. Between 1992 and 2001, deaths from excessive heat in the United States numbered 2,190, compared with 880 deaths from floods and 150 from hurricanes. The average annual number of fatalities directly attributed to heat in the United States is about 400. The 1995 Chicago heat wave, one of the worst in US history, led to approximately 600 heat-related deaths over a period of five days. Eric Klinenberg has noted that in the United States, the loss of human life in hot spells in summer exceeds that caused by all other weather events combined, including lightning, rain, floods, hurricanes, and tornadoes. Despite the dangers, Scott Sheridan, professor of geography at Kent State University, found that less than half of people 65 and older abide by heat-emergency recommendations like drinking lots of water. In his study of heat-wave behavior, focusing particularly on seniors in Philadelphia, Phoenix, Toronto, and Dayton, Ohio, he found that people over 65 "don't consider themselves seniors." "Heat doesn't bother me much, but I worry about my neighbors," said one of his older respondents. According to the Agency for Health care Research and Quality, about 6,200 Americans are hospitalized each summer due to excessive heat, and those at highest risk are poor, uninsured or elderly.
Underreporting and "Harvesting" effect The number of heat fatalities is likely highly underreported due to lack of reports and misreports. Part of the mortality observed during a heat wave, however, can be attributed to a so-called "harvesting effect", a term for a short-term forward mortality displacement. It has been observed that for some heat waves, there is a compensatory decrease in overall mortality during the subsequent weeks after a heat wave. Such compensatory reduction in mortality suggests that heat affects especially those so ill that they "would have died in the short term anyway".
Psychological and sociological effects In addition to physical stress, excessive heat causes psychological stress, to a degree which affects performance, and is also associated with an increase in violent crime.
Power outage Heat waves often lead to electricity spikes due to increased air conditioning use, which can create power outages, exacerbating the problem. During the 2006 North American heat wave, thousands of homes and businesses went without power, especially in California. In Los Angeles, electrical transformers failed, leaving thousands without power for as long as five days. The 2009 South Eastern Australia Heat Wave caused to the city of Melbourne, Australia to experience some major power disruptions which left over half a million people without power as the heat wave blew transformers and overloaded the power grid.
Physical damage Heat waves can and do cause roads and highways to buckle, water lines to burst, power transformers to detonate, causing fires. See the 2006 North American heat wave article about heat waves causing physical damage.
History The record for the longest heat wave in the world is generally accepted to have been set in Marble Bar in Australia, where from October 31, 1923 to April 7, 1924 the temperature broke the 37.8 °C (100.0 °F) benchmark, setting the heat wave record at 160 days.
20th century The 1936 North American heat waves during the Dust Bowl, followed the one of the coldest winters on record—the 1936 North American cold wave. Massive Heat waves across North America were persistent in the 1930s; many mid-Atlantic/Ohio valley states recorded their highest temperatures during July 1934. The longest continuous string of 100 °F (38 °C) or higher temperatures was reached for 101 days in Yuma, Arizona during 1937 and the highest temperatures ever reached in Canada were recorded in two locations in Saskatchewan in July 1937. The heat waves of 1972 in New York and Northeastern United States were significant. Almost 900 people perished; the heat conditions lasted almost 16 days. An estimated 10,000 people perished in the 1980 United States heat wave and drought, which impacted the central and eastern United States. Temperatures were highest in the southern plains. From June through September, temperatures remained above 90 °F (32 °C) all but two days in Kansas City, Missouri. The Dallas/Fort Worth area experienced 42 consecutive days with high temperatures above 100 °F (38 °C), with temperatures reaching 117 °F (47 °C) at Wichita Falls, Texas on June 28. Economic losses were $20 billion (1980 dollars). During another heat wave in the Summer of 1983 temperatures over 100 °F (38 °C) were common across Iowa, Missouri, Illinois, Michigan, Wisconsin, Indiana, Ohio, Minnesota, Nebraska and certain parts of Kentucky; to this day the summer of 1983 remains on record as one of the hottest summers ever recorded in many of the states affected. The hundred-degree readings were accompanied by very dry conditions associated with drought affecting the Corn Belt States and Upper Midwest. The heat also affected the Southeastern U.S. and the Mid-Atlantic states as well that same summer. New York Times represented articles about the heat waves of 1983 affecting the central United States. During 1988 intense heat spells in combination with the drought of 1988 caused deadly results across the United States. Some 5,000 to 10,000 people perished because of constant heat across the United States although-according to many estimates-total death reports run as high as next to 17,000 deaths. The 1995 Chicago heat wave produced record high dew point levels and heat indicies in the Chicagoland area as well in neighboring states like Wisconsin. The lack of emergency
cooling facilities and inadequate response from civic authorities to the senior population, particularly in lower income neighborhoods in Chicago and other Midwest cities, lead to many deaths. The summer of 1999 saw a devastating heat wave and drought in the eastern United States. Rainfall shortages resulted in worst drought on record for Maryland, Delaware, New Jersey, and Rhode Island. The state of West Viriginia was declared a disaster area. 3,810,000 acres (15,400 km2) were consumed by fire as of mid-Aug. Record heat throughout the country resulted in 502 deaths nationwide.
21st century
In early August 2001 an intense heatwave hit the eastern seaboard of the United States and neighboring southeastern Canada. For over a week, temperatures climbed above 35 °C (95 °F) combined with stifling high humidity. Newark, New Jersey tied its alltime record high temperature of 41 °C (106 °F) with a heat index of over 50 °C (122 °F). In April 2002 a summer-like heat wave in spring affected much of the Eastern United States. In the European heat wave of 2003, around 35,000 people died of it. Much of the heat was concentrated in France, where nearly 15,000 people died. In Portugal, the temperatures reached as high as 48 °C (118 °F) in the south. The European heat wave of 2006 was the second massive heat wave to hit the continent in four years, with temperatures rising to 40 °C (104 °F) in Paris; in Ireland, which has a moderate maritime climate, temperatures of over 32 °C (90 °F) were reported. Temperatures of 35 °C (95 °F) were reached in the Benelux and Germany (in some areas 38 °C (100 °F), while Great Britain recorded 37 °C (99 °F). Many heat records were broken (including the hottest ever July temperature in Great Britain) and many people who experienced the heat waves of 1976 and 2003 drew comparisons with them. Highest average July temperatures were recorded at many locations in Great Britain, Netherlands, Denmark, Sweden and Germany. The 2006 North American heat wave affected a wide area of the United States and parts of neighboring Canada during July and August 2006. Over 220 deaths were reported. Temperatures in some parts of South Dakota exceeded 115 °F (46 °C). Also, California experienced temperatures that were extraordinarily high, with records ranging from 100 to 130 °F (38 to 54 °C). On July 22, the County of Los Angeles recorded its highest temperature ever at 119 °F (48 °C). Humidity levels in California were also unusually high, although low compared with normal gulf coast/eastern seaboard summer humidity they were significant enough to cause widespread discomfort. The European heat wave of 2007 affected primarily south-eastern Europe during late June through August. Bulgaria experienced its hottest year on record, with previously unrecorded temperatures above 45 °C (113 °F). The 2007 Greek forest fires were associated with the heat wave. During the 2007 Asian heat wave, the Indian city of Datia experienced temperatures of 48 °C (118 °F). In January 2008, Alice Springs in Australia's Northern Territory recorded ten consecutive days of temperatures above 40 °C (104 °F) with the average temperature for that month being 39.8 °C (103.6 °F). In March 2008, Adelaide, South Australia experienced maximum temperatures of above 35 °C (95 °F) for fifteen consecutive
days, seven days more than the previous longest stretch of 35 °C (95 °F) days. The March 2008 heat wave also included eleven consecutive days above 38 °C (100 °F). The heat wave was especially notable because it occurred in March, an autumn month, in which Adelaide averages only 2.3 days above 35 °C (95 °F). The eastern United States experienced an early Summer heat wave from June 6–10, 2008 with record temperatures.[32] There was a heat wave in Southern California beginning late June, which contributed to widespread fires. On July 6, a renewed heat wave was forecast, which was expected to affect the entire state. In early 2009, Adelaide, South Australia was hit by a heat wave with temperatures reaching 40+ °C for six days in a row, while many rural areas experienced temperatures hovering around about mid 40s °C (mid 110s°F). Kyancutta on the Eyre Peninsula endured at least one day at 48 °C, with 46 and 47 being common in the hottest parts of the state. Melbourne, in neighbouring Victoria recorded 3 consecutive days over 43 °C (109 °F), and also recorded its highest ever temperature 8 days later in a secondary heatwave, with the mercury peaking at 46.4 °C (115.5 °F). During this heat wave Victoria suffered from large bushfires which claimed the lives of more than 210 people and destroyed more than 2,500 homes. There were also over half a million people without power as the heatwave blew transformers and the power grid was overloaded. In August 2009, Argentina experienced a period of unusual and exceptionally hot weather during August 24–30, 2009 during the Southern Hemisphere winter, just a month before spring when an unusual and unrecorded winter heat wave hit the country. A shot of tropical heat drawn unusually far southward hiked temperatures 22 degrees above normal in the city of Buenos Aires and across the northern-centre regions of the country. Several records were broken. Even though normal high temperatures for late August are in the lower 15 °C (59 °F), readings topped 30 °C (86 °F) degrees at midweek, then topped out above 32 °C (90 °F) degrees during the weekend. Temperatures hit 33.8 °C (92.8 °F) on 29 August and finally 34.6 °C (94.3 °F) on 30 August in Buenos Aires, making it the hottest day ever recorded in winter breaking the 1996 winter record of 33.7 °C (92.7 °F). In the city of Santa Fe, a remarkable 38.3 °C (100.9 °F) degree on 30 August was registered, notwithstanding the normal high in the upper 15 °C/60°Fs. As per the Meteorological Office of Argentina August 2009 has been the warmest month during winter since official measurements began. The Northern Hemisphere summer heat wave of 2010 affected many areas across the Northern Hemisphere, especially parts of Northeastern China and Southeastern Russia. In June 2010, Eastern Europe experienced very warm conditions. Ruse, Bulgaria hit 36.6 °C (97.9 °F) on the 13th making it the warmest spot in Europe. Other records broken on the 13th includes Vidin, Bulgaria at 35.8 °C (96.4 °F), Sandanski, Bulgaria hitting 35.5 °C (95.9 °F), Lovech and Pazardzhik, Bulgaria at 35.1 °C (95.2 °F) as well as the capital, Sofia, hitting 33.3 °C (91.9 °F). The heat comes from the Sahara desert and is not associated with rain. This helped the situation with high water levels in that part of the continent. On the 14th, several cities were once again above the 35 °C (95 °F) mark even though they didn't break records. The only cities in Bulgaria breaking records were Musala peak hitting 15.2 °C (59.4 °F) and Elhovo hitting 35.6 °C (96.1 °F). On the 15th, Ruse, Bulgaria peaked at 37.2 °C (99.0 °F). Although it was not a record, this was the highest temperature recorded in the country. 5 Bulgarian cities broke records that day: Ahtopol hit 28.6 °C (83.5 °F), Dobrich was
33.8 °C (92.8 °F), Karnobat hit 34 °C (93 °F), Sliven hit 35 °C (95 °F) and Elhovo recorded 36.1 °C (97.0 °F). From July 4-July 9, 2010 the majority of the American East Coast, from the Carolinas to Maine, was gripped in a severe heat wave. Philadelphia, New York, Baltimore, Washington, Raleigh, and even Boston eclipsed 100 °F (38 °C). Many records were broken, some of which dated back to the 1800s, including Wilmington, Delaware's temperature of 103 °F (39 °C) on Wednesday, the 7th, which broke the record of 97 °F (36 °C) from 1897. Philadelphia and New York eclipsed 100 °F (38 °C) for the first time since 2001. Fredrick, Maryland, and Newark, New Jersey, among others topped the century mark (37.8 Celsius) for four days in a row. The UK declared a heatwave, MetOffice Level 2/4, on the 9th July 2010 for South East England and East Anglia. This was after temperatures reached 31.0 degrees Celsius in London and night time temperatures levelled around 21 degrees Celsius. Japanese heat wave of 2010, from July 16 to present, temperatures of high rising to around Japanese cities for long period, above high temperatures of 35.0 °C (95.0 °F) days, 33 days in Kyoto, 29 days in Tottori and 25 days in Osaka. According to Japan Meteological Agency report, some of Japanese cities record of highest temperature in September, since 1868. 39.9 °C (103.8 °F) hitting in Kyotanabe, Kyoto, 39.1 °C (102.4 °F) hitting in Gujo, Gifu, and above high of 30.0 °C (86.0 °F) is 653 cities, 35.0 °C (95.0 °F) is 128 cities during September 4 to 5, 2010.
J) Lightning Lightning is an atmospheric discharge of electricity accompanied by thunder, which typically occurs during thunderstorms, and sometimes during volcanic eruptions or dust storms. In the atmospheric electrical discharge, a leader of a bolt of lightning can travel at speeds of 220,000 km/h (140,000 mph), and can reach temperatures approaching 30,000 °C (54,000 °F), hot enough to fuse silica sand into glass channels known as fulgurites which are normally hollow and can extend some distance into the ground. There are some 16 million lightning storms in the world every year. Lightning can also occur within the ash clouds from volcanic eruptions, or can be caused by violent forest fires which generate sufficient dust to create a static charge. How lightning initially forms is still a matter of debate: Scientists have studied root causes ranging from atmospheric perturbations (wind, humidity, friction, and atmospheric pressure) to the impact of solar wind and accumulation of charged solar particles.[4] Ice inside a cloud is thought to be a key element in lightning development, and may cause a forcible separation of positive and negative charges within the cloud, thus assisting in the formation of lightning. The irrational fear of lightning (and thunder) is astraphobia. The study or science of lightning is called fulminology, and someone who studies lightning is referred to as a fulminologist.
History of lightning research Benjamin Franklin (1706–1790) endeavored to test the theory that sparks shared some similarity with lightning by using a spire which was being erected in Philadelphia, United States. While waiting for completion of the spire, he got the idea to use a flying object such as a kite. During the next thunderstorm, which was in June 1752, it was reported that he raised a kite. He was accompanied by his son as an assistant. On his end of the string he attached a key, and he tied it to a post with a silk thread. As time passed, Franklin noticed the loose fibers on the string stretching out; he then brought his hand close to the key and a spark jumped the gap. The rain which had fallen during the storm had soaked the line and made it conductive. Franklin was not the first to perform the kite experiment. Thomas-François Dalibard and De Lors conducted it at Marly-la-Ville in France, a few weeks before Franklin's experiment. In his autobiography (written 1771–1788, first published 1790), Franklin clearly states that he performed this experiment after those in France, which occurred weeks before his own experiment, without his prior knowledge as of 1752. As news of the experiment and its particulars spread, others attempted to replicate it. However, experiments involving lightning are always risky and frequently fatal. One of the most well-known deaths during the spate of Franklin imitators was that of Professor Georg Richmann of Saint Petersburg, Russia. He created a set-up similar to Franklin's, and was attending a meeting of the Academy of Sciences when he heard thunder. He ran home with his engraver to capture the event for posterity. According to reports, while the experiment was under way, ball lightning appeared and collided with Richmann's head, killing him. Although experiments from the time of Benjamin Franklin showed that lightning was a discharge of static electricity, there was little improvement in theoretical understanding of lightning (in particular how it was generated) for more than 150 years. The impetus for new research came from the field of power engineering: as power transmission lines came into service, engineers needed to know much more about lightning in order to adequately protect lines and equipment. In 1900, Nikola Tesla generated artificial lightning by using a large Tesla coil, enabling the generation of enormously high voltages sufficient to create lightning.
Properties An average bolt of negative lightning carries an electric current of 30,000 amperes ("amps") — 30 "kiloamps" (kA), and transfers five coulombs of electric charge and 500 million joules — 500 "megajoules" (MJ) of energy. Large bolts of lightning can carry up to 120 kA and 350 coulombs. The voltage is proportional to the length of the bolt. An average bolt of positive lightning carries an electric current of about 300 kA — about 10 times that of negative lightning. Lightning leader development is not just a matter of the electrical breakdown of air, which are about 3 megavolts per meter (MV/m). The ambient electric fields required for lightning leader propagation can be one or two orders of magnitude (10−2) less than the electrical breakdown strength. The potential ("voltage") gradient inside a well-developed return-stroke channel is on the order of hundreds of volts per meter (V/m) due to intense channel ionization, resulting in a true power output on the order of one megawatt per meter
(MW/m) for a vigorous return stroke current of 100 kA. The average peak power output of a single lightning stroke is about one trillion watts — one "terawatt" (1012 W), and the stroke lasts for about 30 millionths of a second — 30 "microseconds". Lightning rapidly heats the air in its immediate vicinity to about 20,000 °C (36,000 °F) — about three times the temperature of the surface of the Sun. This compresses the surrounding clear air and creates a supersonic shock wave which decays to an acoustic wave that is heard as thunder. The return stroke of a lightning bolt follows a charge channel about a centimeter (0.4 in) wide. Different locations have different potentials ("voltages") and currents for an average lightning strike. In the United States, for example, Florida experiences the largest number of recorded strikes in a given period during the summer season, has very sandy soils in some areas, and electrically conductive water-saturated soils in others. As much of Florida lies on a peninsula, it is bordered by the ocean on three sides. The result is the daily development of sea and lake breeze boundaries that collide and produce thunderstorms. NASA scientists have found that electromagnetic radiation created by lightning in clouds only a few miles high can create a "safe zone" in the Van Allen radiation belts that surround the earth. This zone, known as the "Van Allen Belt slot", may be a safe haven for satellites in "middle Earth orbits" (MEOs), protecting them from the Sun's intense radiation.
Formation Positive lightning (a rare form of lightning that originates from positively charged regions of the thundercloud) does not generally fit the preceding pattern.
Electrostatic induction hypothesis According to the electrostatic induction hypothesis charges are driven apart by as-yet uncertain processes. Charge separation appears to require strong updrafts which carry water droplets upward, supercooling them to between -10 and -20 °C. These collide with ice crystals to form a soft ice-water mixture called graupel. The collisions result in a slight positive charge being transferred to ice crystals, and a slight negative charge to the graupel. Updrafts drive the less heavy ice crystals upwards, causing the cloud top to accumulate increasing positive charge. Gravity causes the heavier negatively charged graupel to fall toward the middle and lower portions of the cloud, building up an increasing negative charge. Charge separation and accumulation continue until the electrical potential becomes sufficient to initiate a lightning discharge, which occurs when the distribution of positive and negative charges forms a sufficiently strong electric field.
Polarization mechanism hypothesis The mechanism by which charge separation happens is still the subject of research. Another hypothesis is the polarization mechanism, which has two components: 1. Falling droplets of ice and rain become electrically polarized as they fall through the Earth's natural electric field; 2. Colliding ice particles become charged by electrostatic induction (see above).
There are several additional hypotheses for the origin of charge separation.
Leader formation and the return stroke As a thundercloud moves over the surface of the Earth, an electric charge equal to but opposite the charge of the base of the thundercloud is induced in the Earth below the cloud. The induced ground charge follows the movement of the cloud, remaining underneath it. An initial bipolar discharge, or path of ionized air, starts from a negatively charged mixed water and ice region in the thundercloud. Discharge ionized channels are known as leaders. The positive and negative charged leaders, generally a "stepped leader", proceed in opposite directions. The negative charged one proceed downward in a number of quick jumps (steps). 90 percent of the leaders exceed 45 m (148 ft) in length, with most in the order of 50 to 100 m (164 to 492 feet). As it continues to descend, the stepped leader may branch into a number of paths. The progression of stepped leaders takes a comparatively long time (hundreds of milliseconds) to approach the ground. This initial phase involves a relatively small electric current (tens or hundreds of amperes), and the leader is almost invisible when compared with the subsequent lightning channel. When a stepped leader approaches the ground, the presence of opposite charges on the ground enhances the strength of the electric field. The electric field is strongest on groundconnected objects whose tops are closest to the base of the thundercloud, such as trees and tall buildings. If the electric field is strong enough, a conductive discharge (called a positive streamer) can develop from these points. This was first theorized by Heinz Kasemir. As the field increases, the positive streamer may evolve into a hotter, higher current leader which eventually connects to the descending stepped leader from the cloud. It is also possible for many streamers to develop from many different objects simultaneously, with only one connecting with the leader and forming the main discharge path. Photographs have been taken on which non-connected streamers are clearly visible. Once a channel of ionized air is established between the cloud and ground this becomes a path of least resistance and allows for a much greater current to propagate from the Earth back up the leader into the cloud. This is the return stroke and it is the most luminous and noticeable part of the lightning discharge.
Discharge When the electric field becomes strong enough, an electrical discharge (the bolt of lightning) occurs within clouds or between clouds and the ground. During the strike, successive portions of air become a conductive discharge channel as the electrons and positive ions of air molecules are pulled away from each other and forced to flow in opposite directions. The electrical discharge rapidly superheats the discharge channel, causing the air to expand rapidly and produce a shock wave heard as thunder. The rolling and gradually dissipating rumble of thunder is caused by the time delay of sound coming from different portions of a long stroke.
Gurevich's runaway breakdown theory A theory of lightning initiation, known as the "runaway breakdown theory", proposed by Aleksandr Gurevich of the Lebedev Physical Institute in 1992 suggests that lightning strikes are triggered by cosmic rays which ionize atoms, releasing electrons that are accelerated by the electric fields, ionizing other air molecules and making the air conductive by a runaway breakdown, then "seeding" a lightning strike.
Gamma rays and the runaway breakdown theory It has been discovered in the past 15 years that among the processes of lightning is some mechanism capable of generating gamma rays, which escape the atmosphere and are observed by orbiting spacecraft. Brought to light by NASA's Gerald Fishman in 1994 in an article in Science, these so-called terrestrial gamma-ray flashes (TGFs) were observed by accident, while he was documenting instances of extraterrestrial gamma ray bursts observed by the Compton Gamma Ray Observatory (CGRO). TGFs are much shorter in duration, however, lasting only about 1 ms. Professor Umran Inan of Stanford University linked a TGF to an individual lightning stroke occurring within 1.5 ms of the TGF event, proving for the first time that the TGF was of atmospheric origin and associated with lightning strikes. CGRO recorded only about 77 events in 10 years; however, more recently the RHESSI spacecraft, as reported by David Smith of UC Santa Cruz, has been observing TGFs at a much higher rate, indicating that these occur about 50 times per day globally (still a very small fraction of the total lightning on the planet). The energy levels recorded exceed 20 MeV. Scientists from Duke University have also been studying the link between certain lightning events and the mysterious gamma ray emissions that emanate from the Earth's own atmosphere, in light of newer observations of TGFs made by RHESSI. Their study suggests that this gamma radiation fountains upward from starting points at surprisingly low altitudes in thunderclouds. Steven Cummer, from Duke University's Pratt School of Engineering, said, "These are higher energy gamma rays than come from the sun. And yet here they are coming from the kind of terrestrial thunderstorm that we see here all the time." Early hypotheses of this pointed to lightning generating high electric fields at altitudes well above the cloud, where the thin atmosphere allows gamma rays to easily escape into space, known as "relativistic runaway breakdown", similar to the way sprites are generated. Subsequent evidence has cast doubt, though, and suggested instead that TGFs may be produced at the tops of high thunderclouds. Though hindered by atmospheric absorption of the escaping gamma rays, these theories do not require the exceptionally high electric fields that high altitude theories of TGF generation rely on. The role of TGFs and their relationship to lightning remains a subject of ongoing scientific study.
Re-strike High speed videos (examined frame-by frame) show that most lightning strikes are made up of multiple individual strokes. A typical strike is made of 3 to 4 strokes. There may be more. Each re-strike is separated by a relatively large amount of time, typically 40 to 50 milliseconds. Re-strikes can cause a noticeable "strobe light" effect. Each successive stroke is preceded by intermediate dart leader strokes akin to, but weaker than, the initial stepped leader. The stroke usually re-uses the discharge channel taken by the previous stroke. The variations in successive discharges are the result of smaller regions of charge within the cloud being depleted by successive strokes. The sound of thunder from a lightning strike is prolonged by successive strokes.
Types Some lightning strikes exhibit particular characteristics; scientists and the general public have given names to these various types of lightning. The lightning that is mostcommonly observed is streak lightning. This is nothing more than the return stroke, the visible part of the lightning stroke. The majority of strokes occur inside a cloud so we do not see most of the individual return strokes during a thunderstorm.
Cloud-to-ground lightning This is the best known and second most common type of lightning. Of all the different types of lightning, it poses the greatest threat to life and property since it strikes the ground. Cloud-to-ground lightning is a lightning discharge between a cumulonimbus cloud and the ground. It is initiated by a leader stroke moving down from the cloud.
Bead lightning Bead lightning is a type of cloud-to-ground lightning which appears to break up into a string of short, bright sections, which last longer than the usual discharge channel. It is relatively rare. Several theories have been proposed to explain it; one is that the observer sees portions of the lightning channel end on, and that these portions appear especially bright. Another is that, in bead lightning, the width of the lightning channel varies; as the lightning channel cools and fades, the wider sections cool more slowly and remain visible longer, appearing as a string of beads.
Ribbon lightning Ribbon lightning occurs in thunderstorms with high cross winds and multiple return strokes. The wind will blow each successive return stroke slightly to one side of the previous return stroke, causing a ribbon effect.
Staccato lightning Staccato lightning is a cloud to ground lightning strike which is a short-duration stroke that appears as a single very bright flash and often has considerable branching.
Forked lightning Forked lightning is a name, not in formal usage, for cloud-to-ground lightning that exhibits branching of its path.
Ground-to-cloud lightning Ground-to-cloud lightning is a lightning discharge between the ground and a cumulonimbus cloud initiated by an upward-moving leader stroke. This type of lightning forms when negatively charged ions called the stepped leader rises up from the ground and meets the positively charged ions in a cumulonimbus cloud. Then the strike goes back to the ground as the return stroke.
Cloud-to-cloud lightning Lightning discharges may occur between areas of cloud without contacting the ground. When it occurs between two separate clouds it is known as inter-cloud lightning and when it occurs between areas of differing electric potential within a single cloud, it is known as intra-cloud lightning. Intra-cloud lightning is the most frequently occurring type. These are most common between the upper anvil portion and lower reaches of a given thunderstorm. This lightning can sometimes be observed at great distances at night as socalled "heat lightning". In such instances, the observer may see only a flash of light without hearing any thunder. The "heat" portion of the term is a folk association between locally experienced warmth and the distant lightning flashes. Another terminology used for cloud-cloud or cloud-cloud-ground lightning is "Anvil Crawler", due to the habit of the charge typically originating from beneath or within the anvil and scrambling through the upper cloud layers of a thunderstorm, normally generating multiple branch strokes which are dramatic to witness. These are usually seen as a thunderstorm passes over the observer or begins to decay. The most vivid crawler behavior occurs in well developed thunderstorms that feature extensive rear anvil shearing.
Sheet lightning Sheet lightning is an informally applied name to cloud-to-cloud lightning that exhibits a diffuse brightening of the surface of a cloud caused by the actual discharge path being hidden. Also it can be applied when the lightning itself cannot be seen by the spectator, so it appears as only a flash, or a sheet of light.
Heat lightning Heat lightning is a common name for a lightning flash that appears to produce no thunder because it occurs too far away for the thunder to be heard. The sound waves dissipate before they reach the observer.
Dry lightning Dry lightning is a term in Canada and the United States for lightning that occurs with no precipitation at the surface. This type of lightning is the most common natural cause of wildfires. Pyrocumulus clouds produce lightning for the same reason that it is produced by cumulonimbus clouds. When the higher levels of the atmosphere are cooler, and the surface is warmed to extreme temperatures due to a wildfire, volcano, etc., convection will occur, and the convection produces lightning. Therefore, fire can beget dry lightning through the development of more dry thunderstorms which cause more fires (see positive feedback).
Rocket lightning It is a form of cloud discharge, generally horizontal and at cloud base, with a luminous channel appearing to advance through the air with visually resolvable speed, often intermittently.
Positive lightning Positive lightning is a type of lightning strike that comes from apparently clear or only slightly cloudy skies; they are also known as "bolts from the blue" because of this trait. Unlike the more common negative lightning, the positive charge is carried by the top of the clouds (generally anvil clouds) rather than the ground. The leader forms in the sky travelling horizontally for several miles before veering down to meet the negatively charged streamer rising from below. Positive lightning makes up less than 5% of all lightning strikes. Because of the much greater distance they must travel before discharging, positive lightning strikes typically carry six to ten times the charge and voltage difference of a negative bolt and last around ten times longer. During a positive lightning strike, huge quantities of ELF and VLF radio waves are generated. As a result of their greater power, as well as lack of warning, positive lightning strikes are considerably more dangerous. At the present time, aircraft are not designed to withstand such strikes, since their existence was unknown at the time standards were set and the dangers unappreciated until the destruction of a glider in 1999. The standard in force at the time of the crash, Advisory Circular AC 20-53A, was replaced by Advisory Circular AC 2053B in 2006, however it is unclear whether adequate protection against positive lighting was incorporated. Positive lightning is also now believed to have been responsible for the 1963 in-flight explosion and subsequent crash of Pan Am Flight 214, a Boeing 707. Due to the dangers of lightning, aircraft operating in U.S. airspace have been required to have lightning discharge wicks to reduce the damage by a lightning strike, but these measures may be insufficient for positive lightning.
Positive lightning has also been shown to trigger the occurrence of upper atmosphere lightning. It tends to occur more frequently in winter storms, as with thunders now, and at the end of a thunderstorm.
Ball lightning Ball lightning may be an atmospheric electrical phenomenon, the physical nature of which is still controversial. The term refers to reports of luminous, usually spherical objects which vary from pea-sized to several meters in diameter. It is sometimes associated with thunderstorms, but unlike lightning flashes, which last only a fraction of a second, ball lightning reportedly lasts many seconds. Ball lightning has been described by eyewitnesses but rarely recorded by meteorologists. Scientific data on natural ball lightning is scarce owing to its infrequency and unpredictability. The presumption of its existence is based on reported public sightings, and has therefore produced somewhat inconsistent findings. Laboratory experiments have produced effects that are visually similar to reports of ball lightning, but at present, it is unknown whether these are actually related to any naturally occurring phenomenon. One theory is that ball lightning may be created when lightning strikes silicon in soil, a phenomenon which has been duplicated in laboratory testing. Given inconsistencies and the lack of reliable data and completely contradicting and unpredictable behavior, the true nature of ball lightning is still unknown and was often regarded as a fantasy or a hoax. Reports of the phenomenon were dismissed for lack of physical evidence, and were often regarded the same way as UFO sightings. Severely contradicting descriptions of ball lightning makes it impossible even to create plausible hypothesis that will take into account described behavior. One theory that may account for this wider spectrum of observational evidence is the idea of combustion inside the low-velocity region of spherical vortex breakdown of a natural vortex (e.g., the 'Hill's spherical vortex'). Natural ball lightning appears infrequently and unpredictably, and is therefore rarely (if ever truly) photographed. However, several purported photos and videos exist. Perhaps the most famous story of ball lightning unfolded when 18th-century physicist Georg Wilhelm Richmann installed a lightning rod in his home and was struck in the head - and killed - by a "pale blue ball of fire."
Upper-atmospheric lightning Reports by scientists of strange lightning phenomena about storms date back to at least 1886. However, it is only in recent years that fuller investigations have been made. This has sometimes been called mega lightning.
Sprites Sprites are large-scale electrical discharges that occur high above a thunderstorm cloud, or cumulonimbus, giving rise to a quite varied range of visual shapes. They are triggered by the discharges of positive lightning between the thundercloud and the ground. The phenomena were named after the mischievous sprite (air spirit) Puck in Shakespeare's A Midsummer Night's Dream. They normally are coloured reddish-orange or greenish-blue, with hanging tendrils below and arcing branches above their location, and can be preceded by a reddish halo. They often occur in clusters, lying 50 miles (80 km) to 90 miles (145 km)
above the Earth's surface. Sprites were first photographed on July 6, 1989 by scientists from the University of Minnesota and have since been witnessed tens of thousands of times. Sprites have been mentioned as a possible cause in otherwise unexplained accidents involving high altitude vehicular operations above thunderstorms.
Blue jets Blue jets differ from sprites in that they project from the top of the cumulonimbus above a thunderstorm, typically in a narrow cone, to the lowest levels of the ionosphere 25 miles (40 km) to 50 miles (80 km) above the earth. They are also brighter than sprites and, as implied by their name, are blue in colour. They were first recorded on October 21, 1989, on a video taken from the space shuttle as it passed over Australia, and subsequently extensively documented in 1994 during aircraft research flights by the University of Alaska. On September 14, 2001, scientists at the Arecibo Observatory photographed a huge jet double the height of those previously observed, reaching around 50 miles (80 km) into the atmosphere. The jet was located above a thunderstorm over the ocean, and lasted under a second. Lightning was initially observed traveling up at around 50,000 m/s in a similar way to a typical blue jet, but then divided in two and sped at 250,000 m/s to the ionosphere, where they spread out in a bright burst of light. On July 22, 2002, five gigantic jets between 60 and 70 km (35 to 45 miles) in length were observed over the South China Sea from Taiwan, reported in Nature. The jets lasted under a second, with shapes likened by the researchers to giant trees and carrots.
Elves Elves often appear as dim, flattened, expanding glows around 250 miles (402 km) in diameter that last for, typically, just one millisecond. They occur in the ionosphere 60 miles (97 km) above the ground over thunderstorms. Their colour was a puzzle for some time, but is now believed to be a red hue. Elves were first recorded on another shuttle mission, this time recorded off French Guiana on October 7, 1990. Elves is an acronym for Emissions of Light and Very Low Frequency Perturbations from Electromagnetic Pulse Sources. This refers to the process by which the light is generated; the excitation of nitrogen molecules due to electron collisions (the electrons possibly having been energized by the electromagnetic pulse caused by a discharge from the Ionosphere).
Triggered lightning Lightning has been triggered by launching lightning rockets carrying spools of wire into thunderstorms. The wire unwinds as the rocket ascends, providing a path for lightning. These bolts are typically very straight due to the path created by the wire. Lightning has also been triggered directly by other human activities: Flying aircraft can trigger lightning. Furthermore, lightning struck Apollo 12 soon after takeoff, and has struck soon after thermonuclear explosions.
Volcanically triggered There are three types of volcanic lightning:
Extremely large volcanic eruptions, which eject gases and material high into the atmosphere, can trigger lightning. This phenomenon was documented by Pliny the Elder during the AD79 eruption of Vesuvius, in which he perished. An intermediate type which comes from a volcano's vents, sometimes 1.8 miles (3 kilometers) long. Small spark type lightning about 3 feet (1 meter) long lasting a few milliseconds.
Laser-triggered Since the 1970s, researchers have attempted to trigger lightning strikes by means of infrared or ultraviolet lasers, which create a channel of ionized gas through which the lightning would be conducted to ground. Such triggered lightning is intended to protect rocket launching pads, electric power facilities, and other sensitive targets. In New Mexico, U.S., scientists tested a new terawatt laser which provoked lightning. Scientists fired ultra-fast pulses from an extremely powerful laser thus sending several terawatts into the clouds to call down electrical discharges in storm clouds over the region. The laser beams sent from the laser make channels of ionized molecules known as "filaments". Before the lightning strikes earth, the filaments lead electricity through the clouds, playing the role of lightning rods. Researcher’s generated filaments that lived too short a period to trigger a real lightning strike. Nevertheless, a boost in electrical activity within the clouds was registered. According to the French and German scientists, who ran the experiment, the fast pulses sent from the laser will be able to provoke lightning strikes on demand. Statistical analysis showed that their laser pulses indeed enhanced the electrical activity in the thundercloud where it was aimed—in effect they generated small local discharges located at the position of the plasma channels.
Extraterrestrial lightning Lightning requires the electrical breakdown of a gas, so it cannot exist in a visual form in the vacuum of space. However, lightning has been observed within the atmospheres of other planets, such as Venus, Jupiter and Saturn. Lightning on Venus is still a controversial subject after decades of study. During the Soviet Venera and U.S. Pioneer missions of the 1970s and '80s, signals suggesting lightning may be present in the upper atmosphere were detected. However, recently the Cassini-Huygens mission fly-by of Venus detected no signs of lightning at all. Despite this, it has been suggested that radio pulses recorded by the spacecraft Venus Express may originate from lightning on Venus.
Trees and lightning Trees are frequent conductors of lightning to the ground. Since sap is a poor conductor, its electrical resistance causes it to be heated explosively into steam, which blows off the bark outside the lightning's path. In following seasons trees overgrow the damaged area and may cover it completely, leaving only a vertical scar. If the damage is severe, the tree may not be able to recover, and decay sets in, eventually killing the tree. In sparsely populated areas such as the Far East and Siberia, lightning strikes are one of the major causes of forest fires. The smoke and mist expelled by a forest fire can cause electric charges, multiplying the intensity of a forest fire. It is commonly thought that a tree standing alone is
more frequently struck, though in some forested areas, lightning scars can be seen on almost every tree. The two most frequently struck tree types are the oak and the elm. Pine trees are also quite often hit by lightning. Unlike the oak, which has a relatively shallow root structure, pine trees have a deep central root system that goes down into the water table. Pine trees usually stand taller than other species, which also makes them a likely target. Factors which lead to its being targeted are high resin content, loftiness, and its needles which lend themselves to a high electrical discharge during a thunderstorm. Trees are natural lightning conductors, and are known to provide protection against lightning damages to the nearby buildings. Tall trees with high biomass for the root system provide good lightning protection. An example is the teak tree (Tectona grandis), which grows to a height of 45 metres (147.6 ft). It has a spread root system with a spread of 5 m and a biomass of 4 times that of the trunk; its penetration into the soil is 1.25 metres (4.10 ft) and has no tap root. When planted near a building, its height helps in catching the oncoming lightning leader, and the high biomass of the root system helps in dissipation of the lightning charges. Lightning currents have a very fast risetime, on the order of 40 kA per microsecond. Hence, conductors of such currents exhibit marked skin effect, causing most of the currents to flow through the conductor skin. The effective resistance of the conductor is consequently very high and therefore, the conductor skin gets heated up much more than the conductor core. When a tree acts as a natural lightning conductor, due to skin effect most of the lightning currents flow through the skin of the tree and the sap wood. As a result, the skin gets burnt and may even peel off. The moisture in the skin and the sap wood evaporates instantaneously and may get split.
Lightning detection The earliest detector invented to warn of the approach of a thunder storm was the lightning bell. Benjamin Franklin installed one such device in his house. The detector was based on an electrostatic device called the 'electric chimes' invented by Andrew Gordon in 1742. Lightning discharges generate a wide range of electromagnetic radiations, including radio-frequency pulses. The times at which a pulse from a given lightning discharge arrive at several receivers can be used to locate the source of the discharge. The United States federal government has constructed a nation-wide grid of such lightning detectors, allowing lightning discharges to be tracked in real time throughout the continental U.S. In addition to ground-based lightning detection, several instruments aboard satellites have been constructed to observe lightning distribution. These include the Optical Transient Detector (OTD), aboard the OrbView-1 satellite launched on April 3, 1995, and the subsequent Lightning Imaging Sensor (LIS) aboard TRMM launched on November 28, 1997.
Notable lightning strikes Some lightning strikes have caused either numerous fatalities or great damage. The following is a partial list:
A particularly deadly lightning incident occurred in Brescia, Italy in 1769. Lightning struck the Church of St. Nazaire, igniting the 100 tons of gunpowder in its vaults; the resulting explosion killed 3000 people and destroyed a sixth of the city. 1902: A lightning strike damaged the upper section of the Eiffel Tower, requiring the reconstruction of its top December 8, 1963: Pan Am Flight 214 crashed as result of a lightning strike, and 81 people were killed. July 12, 1970, the central mast of the Orlunda radio transmitter collapsed after a lightning strike destroyed its basement insulator. December 24, 1971: LANSA Flight 508 crashed as a result of lightning in Peru, with 91 people killed. November 2, 1994, lightning struck fuel tanks in Dronka, Egypt and caused 469 fatalities.
Harvesting lightning energy Since the late 1980s there have been several attempts to investigate the possibility of harvesting energy from lightning. While a single bolt of lightning carries a relatively large amount of energy, this energy is concentrated in a small location and is passed during an extremely short period of time (milliseconds); therefore, extremely high electrical power is involved. It has been proposed that the energy contained in lightning be used to generate hydrogen from water, or to harness the energy from rapid heating of water due to lightning. A technology capable of harvesting lightning energy would need to be able to capture rapidly the high power involved in a lightning bolt. Several schemes have been proposed, but the high energy involved in each lightning bolt render lightning power harvesting from ground based lightning rods as impractical. According to Northeastern University physicists Stephen Reucroft and John Swain, a lightning bolt carries a few million joules of energy, enough to power a 100-watt bulb for 5.5 hours. Additionally, lightning is sporadic, and therefore energy would have to be collected and stored; it is difficult to convert high-voltage electrical power to the lower-voltage power that can be stored. In the summer of 2007, an alternative energy company called Alternate Energy Holdings (AEH) tested a method for capturing the energy in lightning bolts. The design for the system had been purchased from an Illinois inventor named Steve LeRoy, who had reportedly been able to power a 60-watt light bulb for 20 minutes using the energy captured from a small flash of artificial lightning. The method involved a tower, a means of shunting off a large portion of the incoming energy, and a capacitor to store the rest. According to Donald Gillispie, CEO of AEH, they "couldn't make it work," although "given enough time and money, you could probably scale this thing up... it's not black magic; it's truly math and science, and it could happen." According to Dr. Martin A. Uman, co-director of the Lightning Research Laboratory at the University of Florida and a leading authority on lightning, a single lighting strike, while fast and bright, contains very little energy, and dozens of lighting towers like those used in the system tested by AEH would be needed to operate five 100-watt light bulbs for the course of a year. When interviewed by The New York Times, he stated that the energy in a thunderstorm is comparable to that of an atomic bomb, but trying to harvest the energy of lightning from the ground is "hopeless".
A relatively easy method is the direct harvesting of atmospheric charge before it turns into lighting. At a small scale, it was done a few times with the most known example being Benjamin Franklin's experiment with his kite. However, to collect reasonable amounts of energy very large constructions are required, and it is relatively hard to utilize the resulting extremely high voltage with reasonable efficiency.
Ceraunoscopy This is divination by observing lightning or by listening to thunder. It is a type of aeromancy. People have also sought to control lightning by conducting rituals or casting spells.
K) Extreme weather Extreme weather includes weather phenomena that are at the extremes of the historical distribution, especially severe or unseasonal weather. The most commonly used definition of extreme weather is based on an event's climatological distribution. Extreme weather occurs only 5% or less of the time. According to climate scientists and meteorological researchers, extreme weather events are rare.
Extreme temperatures Heat waves Heat waves can often have severe effects upon the landscape, causing famine, destruction of vegetation, and possible deaths to livestock and wildlife. Heat waves are long periods of abnormally high temperatures. There is generally no universal definition of a heat wave because of the variation within temperatures are different in geographic locations. Along with the excessive heat, they are often accompanied by high levels of humidity. These two characteristics increase the relative temperature or heat index to dangerous levels. Because heat waves are not visible as other forms of severe weather are, like hurricanes, tornadoes, and thunderstorms, they are one of the less known forms of extreme weather. This severe weather phenomena can damage populations and crops due potential dehydration or hyperthermia. Heat cramps, heat expansion, heat stroke, and dehydration can result in human populations. The dried soils are more susceptible to erosion, decreasing lands available for agriculture. Outbreaks of wildfires can increase in frequency as dry vegetation has increased likeliness of igniting. The evaporation of bodies of water can be devastating to marine populations, decreasing the size of the habitats available as well as amount of nutrition presented within the waters. Livestock and other animal populations may decline as well. Power outages can also occur within areas experiencing heatwaves due to the increased demand for electricity. The urban heat island effect can increase temperatures even more, particularly overnight.
Cold waves A cold wave is a weather phenomenon that is distinguished by a cooling of the air. Specifically, as used by the U.S. National Weather Service, a cold wave is a rapid fall in temperature within a 24 hour period requiring substantially increased protection to agriculture, industry, commerce, and social activities. The precise criterion for a cold wave is determined by the rate at which the temperature falls, and the minimum to which it falls. This minimum temperature is dependent on the geographical region and time of year. Cold waves generally are capable of occurring any geological location and are formed by large cool air masses that accumulate over certain regions, caused by movements of air streams. A cold wave can cause death and injury to livestock and wildlife. Exposure to cold mandates greater caloric intake for all animals, including humans, and if a cold wave is accompanied by heavy and persistent snow, grazing animals may be unable to reach necessary food and water, and die of hypothermia or starvation. Cold waves often necessitate the purchase of fodder for livestock at considerable cost to farmers. Human populations can be inflicted with frostbites when exposed for extended periods of time to cold and may result in the loss of limbs or damage to internal organs. Extreme winter cold often causes poorly insulated water pipes to freeze. Even some poorly-protected indoor plumbing may rupture as frozen water expands within them, causing property damage. Fires, paradoxically, become more hazardous during extreme cold. Water mains may break and water supplies may become unreliable, making firefighting more difficult. Cold waves that bring unexpected freezes and frosts during the growing season in mid-latitude zones can kill plants during the early and most vulnerable stages of growth. This results in crop failure as plants are killed before they can be harvested economically. Such cold waves have caused famines. Cold waves can also cause soil particles to harden and freeze, making it harder for plants and vegetation to grow within these areas. One extreme was the so-called Year without a summer of 1816; one of several years during the 1810s in which numerous crops failed during freakish summer cold snaps after volcanic eruptions reduced incoming sunlight and the temperature of the Earth's core.
Related to significant tropical cyclones Increasing dramatic weather catastrophes are due to an increase in the number of severe events and an increase in population densities, which increase the number of people affected and damage caused by an event of given severity. The World Meteorological Organization[8] and the U.S. Environmental Protection Agency[9] have linked increasing extreme weather events to global warming, as have Hoyos et al. (2006), writing that the increasing number of category 4 and 5 hurricanes is directly linked to increasing temperatures.[10] Similarly, Kerry Emanuel in Nature writes that hurricane power dissipation is highly correlated with temperature, reflecting global warming.[11] Hurricane modeling has produced similar results, finding that hurricanes, simulated under warmer, high CO2 conditions, are more intense than under present-day conditions. Thomas Knutson and Robert E. Tuleya of the NOAA stated in 2004 that warming induced by greenhouse gas may lead to increasing occurrence of highly destructive category-5 storms.[12] Vecchi and Soden find that wind shear, the increase of which acts to inhibit tropical cyclones, also changes in model-
projections of global warming. There are projected increases of wind shear in the tropical Atlantic and East Pacific associated with the deceleration of the Walker circulation, as well as decreases of wind shear in the western and central Pacific.[13] The study does not make claims about the net effect on Atlantic and East Pacific hurricanes of the warming and moistening atmospheres, and the model-projected increases in Atlantic wind shear.
Management of weather hazards The natural hazard management process can be divided into pre-event measures, actions during and immediately following an event, and post-disaster measures. In approximate chronological order, these are as follows: 1. Pre-event Measures: a. Mitigation of Natural Hazards: -Data Collection and Analysis - Vulnerability Reduction b. Preparation for Natural Disasters: - Prediction - Emergency preparedness (including monitoring, alert, evacuation) - Education and Training 2. Measures During and Immediately after Natural Disasters: a. Rescue b. Relief 3. Post-disaster Measures a. Rehabilitation b. Reconstruction of these, the mitigation mechanisms are most cost effective in reducing loss of life and property and most compatible with the development planning process. The data collection effort refers to data on the hazards themselves, vulnerability, and risk. The mitigation mechanisms are described briefly below.
Community Based Disaster Risk Mitigation:
The poor live with minor and major hazards and disaster risk on a daily basis. Mitigating disaster risk involves reducing vulnerability and improving coping capacities and needs to involve all stakeholders. It is recommended that disaster mitigation is made integral part of regular developmental programs. The introduction of roof rainwater harvesting has mitigated the impacts of the reoccurring droughts in the semi-arid districts in Gujarat in India. When economic opportunities are (made) available, women can use time gains for income generating activities thereby reducing poverty and improving gender relations. Moreover, the women’s income is vital during crisis periods—droughts—and reduces migration.
A newsletter on rainwater harvesting and a series of local capacity building cycles have built the coping capacity of local stakeholders—including government institutions. In addition, this has enhanced the implementation and scaling up of ‘concrete’ programs that address water security
This case study will look at a community based disaster mitigation program that is implemented by the Disaster Mitigation Institute, Ahmedabad, Gujarat, India. This program focuses on drought proofing and consists of the following sub-projects:
construction of roof rainwater harvesting tanks in the districts of Kutch, Surendranagar, and Patan in collaboration with Kutch Craft Association (KCA), Banaskantha DWCRA Mahila SEWA Association (BDMSA), and Surendranagar Mahila and Balvikas Mandal; local capacity building cycles for local government officials, CBOs, NGOs and community members; and rainwater harvesting newsletter published in the local language, Gujarati, in collaboration with the distinguished Centre for Science and Environment (CSE) in Delhi.
DMI, exists with the mission to mitigate and reduce the impact of disasters risks on communities by raising awareness, helping to establish and strengthen sustainable institutional mechanisms, enhancing knowledge and skills, and facilitating exchange of information, experience and expertise captured through local learning. DMI is an organization that has multiple access and presence at grass roots, national and international level in conducting mitigation programs for disaster managers.
The poverty and disasters Poverty means more than inadequate consumption, education, and health. As the voices of the poor cry out, it also means dreading the future—knowing that a crisis may descend at any time, not knowing whether one will cope. Living with such risk is part of life for poor people Poor people are often among the more vulnerable in society because they are the most exposed to a wide array of risks. Their low income means they are less able to save and accumulate assets. That in turn restricts their ability to deal with a crisis when it strikes.” In other words, whether a hazard becomes a disaster is a function of vulnerability to the impacts of the disaster and the capacity to mitigate the impacts. Vulnerability can be defined as the risk that a household or individual will experience a period of income or health poverty over time as well as the probability of being exposed to a number of other risks [World Bank 2000]. Vulnerability is an important aspect of poverty though it should not be equated to it. Some sections of the poor are more vulnerable. For instance, women, children, and elderly people (social vulnerability) and the self-employed, casual labourers, marginal farmers (economic vulnerability). Manageability or capacity is the degree to which an individual or community can intervene and manage a hazard in order to reduce its potential impact. This implies that based on people’s perception of their disaster risk, they are able to make decisions to adapt, to modify, to bypass, to overlook or ignore risk.
Hence, whether a hazard becomes a disaster is highly subjective. For instance, for most marginal farmers droughts are outright disasters as rain fed agriculture is probably his only source of income. Neither does he have the financial reserves to see him through this crisis period or to invest in irrigation infrastructure. A big farmer, however, is likely to be less affected as he has the means to invest in the drilling of borewells and make up for the loss of his seeds. The local moneylender probably welcomes a drought as an opportunity to augment his income and to seize land from marginal farmers. Droughts are a well know example of hazard that forms a constant threat to the livelihoods of the poor in semi-arid areas. Examples of other disasters directly or indirectly linked to water are floods, cyclones and tidal waves, (ground) water pollution, salinity ingress, stagnant water, and so on. However, for the poor, minor and local disasters can be equally devastating, for instance, a well that runs dry, flash floods after heavy rainfall, and arsenic pollution of ground water. Most of these disasters never to make the newspapers. Over the last two decades there has been a growing realization that many top down approaches to disaster risk management fail to address specific local needs of vulnerable communities, ignore the potential of local natural and human resources and capacities and in many cases even increase peoples’ vulnerability. In addition, government institutions—and international relief organisations—do not have the capacity to respond to disaster at a scale and at a speed that is needed. Hence, local communities need to be equipped with knowledge, skills, and coping mechanisms to mitigate disasters and to deal with the impacts of these disasters. However, Governmental and Non-governmental organizations and individual professionals are needed to strengthen the community capacity.
References 1. An Overview of Environmental Hazards Related to Crops in Greece by by Nicolas R. Dalezios, Christos Domenikiotis, Nicos Papageorgiou, Dimitrios Bampzelis, Emmanouil Tsiros, Efi Kanellou, Evanthia Hondronikou, Anna Blanda. UNIVERSITY OF THESSALY, LABORATORY OF AGROMETEOROLOGY. pp -5, 9, 30, 34, 52. 2. Principles of Agronomy by Reddy and Reddy. Kalyani Pub. pp- 28. 3. www.fao.org/ag/locusts 4. www.wikipedia.com 5. POLITECNICO DI MILANO - DIPARTIMENTO DI INGEGNERIA AEROSPAZIALE AIRCRAFT SYSTEMS – LECTURE NOTES, VERSION 2004 Chapter 10 – Weather hazards protection.
