can be found in the Norwegian chronicle. The. King's. Mirror of about. 1250. .... Full moon. Strong aurora. Total starlight. Airglow. (visible). OH. {infrared). Lyman ...... in the following night. This is true in subauroral latitudes only when the storm is ...... the geographical distribution of auroras and thunder storms. Am. J. Sci. and.
N64-28080
,%
X4n1-64-97
g IACCESSION
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TMX-55041
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I_UMBI_RI
k-
AURORA
BY BENGT
HULTQVIST Q
oTS
XER OX MICROFILM
pp, l CE
$ $
APRIL1964
GODDARD SPACEFLIGHTCENTER GREENBELT, MARYLAND
(Goddard
Energetic
Particles
Preprint
Series)
AURORA
a review
Bengt
Goddard
;_NASA-National Post-Doctoral Kiruna
Academy Resident
Geophysical
Hultqvist_
Space
Greenbelt,
by
Flight
of Sciences-National Research
Observatory,
Center
Maryland
Associate Kiruna,
Research on leave Sweden
Council of absence
Senior from
TABLE
I.
Introductory
Description
1. 2.
and Energy Considerations and Classification of Aurora
Intensity Definition
3.
The
4.
Auroral
5.
Emission
6.
Methods
.....................
Development
of
Forms Spectrum of
Figure
1.
for of
Geographical (a)
Introduction
(b)
Observed Latitudinal
Aurora
...................
Section
l and
Aurora
of
.......................
Type
Effects
(f)
Inner
Auroral
of
Time
Seasonal
(c)
Sunspot
Orientation
Activity
Auroral of Visual
of Observational Theoretical Curves
Variation
(b)
17 .........
Zones Auroral
and
Auroral
Zones
Recurrence Variation
on
the
Auroral
of Visual Tendency.
25
27
Activity
Auroral
........
Activity
......
..............
28 31 31
....................
Arcs
20
Z5
31
.................
3Z
.................
3Z
Average
(b)
Diurnal Variation in the Orientation in and the Auroral Zones ................... Discussion Auroral
Orientations
Location
with
...................
Variation
of Auroral
Zones
..................
of Visual
Variations
Cycle
Zone
Auroral ..............
(a)
(c)
17
18
Cycle
Day
16
.........................
Auroral
27
............
17
(e)
(a}
Figures
Auroral
the
Dependence
Other
14
........................ Locations of Distribution
(d)
3.
for
..................
Comparison Various
Diurnal
6 lZ
Visual
(c)
2.
...........
7
Distribution
Solar
Z 4
Display
Studies
Visual
Activity
4.
Auroral
............. ...........
......................
Recording
Captions
Morphology
an
1
........................
Morphological
2.
OF CONTENTS
...................
of the Diurnal Variation Zones .....................
Near
33 Near 34 the 37
(d) Diurnal Variation on the Central Auroral Caps ..... (e) Other Variations in Arc Orientations .......... 5. The Height and Vertical Extent of Visual Aurora 6. Motions ............................
40 41
......
41 44
(a) Changes in the Geographical Pattern of Auroral Activity ........................ (b) Motion of Indivudual Auroral Forms .... ...... 7. Dynamic Morphology of Individual Auroral Displays Figure Captions for Section 2 and Figures ........... 3. Correlation
with
and
Disturbances
Geophysical
Phenomena
....
49 52
......
57
I.
Solar
2. 3.
Geomagnetic Disturbances .................. Earth Currents ........................
57 59
4.
Radio
59
Aurora
5.
Bremstrahlung
6.
Auroral
7. 8.
Ionospheric Scintillation
9. i0.
Radio-Noise Auroral
Figure
57
......................... X-rays
at Balloon
Altitudes
61
2.
Observed
..................
64
• •
.......................
for Section
3 and
Fluxes
and
Energy
into the
Figures
............
68
Associated 71 71
Spectra
Upper
65 66
.........................
Precipitated (a)
.....
65
Observations of Energetic Particles Aurora ..........................
Introduction
60
.......................... Emission
I.
.........
......................
Disturbances Associated with Aurora of Radio Waves from Radio Stars and
"Sound"
Captions
Direct with
......................
Absorption
Satellites
4.
Solar
44 46
of Electrons
Atmosphere
.........
71
Latitudinal Distribution and Other Spatial Characteristics ....................
72
(b)
Time
Characteristics
75
(c)
Pitch
Angle
(d)
Kp -dependence
(e)
The
Spectrum
3.
Observed
Fluxes
4.
Quantitative
Precipitated and
Photon
of Precipitation
Distribution
.................
of Precipitation of Precipitated and
Energy
Emission
Between
Electrons
ii
........
76 77
of Protons .............
Electron
in Aurora
75
.............
Spectra
into the Atmosphere Relations
.........
79
Precipitation
..............
80
5.
Relation
of Precipitated
Radiation Fi'gure So
Captions
Theoretical
Introduction
2.
Some
3.
Closed
4.
Model
Acknowledgements Captions
References
4 and
Figures
82 ............
of the
the
Theoretical
Models
88 Problem
................
Solar
Plasma
Field
.....................
Penetrating
Section
5 and
............................
111
Figures
......
89 90
into the 94
........................ for
87 88
.........................
Magnetosphere with
Outer
.......................
Specifications
Geomagnetic
to the
.........................
for Section
Models
I.
Figure
Belt
Electrons
96 ...........
97 98
i.
Descriptions most (ca
famous
B.C.)),
Pliny
A.D.)),
and
15 (Ca.
sidered
63
In northern
stitions
did not
remarkably
The
and he recent
first
by 1963)
the
northern
analogy
with
australis. the is
upper events
them.
tacular
glow
"The
Merry
isles
of
aurora
the has
explosions. 1958,
French
and
is
of
they
a display
(after made
and
first
by
can
title,
the
Jacka
andPaton,
which
the
aurora 1958).
since
dawn,
by
with
so
it
is
was
of
In
called
aurora
it
latitudes.
those
is
It
parts
of
the
of
the
concealed
no
longer
is
more
known
in In
an aptly
the the
high-altitude
observed
mostly
occasions
1963). use
latitudes.
frequently it
and
been and
is
higher
see
have appearance
been
rare
more
(5acka
latitudes at
are
to
medium
the
(1955)
of
usual
have
super-
extent. chronicle
events
the
middle
on
name
artificial
Waddington,
its like
man
in
overhead
horizon,
belies the
Britain"
is
such
St6rmer
1621,
lights
observers
the
horizon,
Dancers,"
been
which
latitude
then
the
in
observed from
and
same
seems
of
southern seen
by
dawn,
equatorwards
below
Aurora
northern
are
from
common to the
14 con-
superstitions
auroral
Gassendi
the
were
quoted
of
33
auroras
in the Norwegian
description
dawn
middle being
The Fowler
when
moves
that
on
or
and
I, Chaps.
more
It is partly
appropriate
northern
aurora
be found
Z7
5
Book
descriptions
by
are
descriptions
borealis
the
observation
philosopher
an
lights aurora
which,
can
good
and
auroras
1250.
borealis,
the
portion when
display from
aurora
"The
only
great
some
name
used
Paton, of
quotes
rare
of the
I, Chap.
II, Chaps
characterized
objective
description of about
the
Some
Book
Book
calamities
where the
known.
Naturales,
Europe
are
Europe
Mirror
also time.
The
coming
influence good
King's
Naturalis,
(Quaestiones
especially,
are
(Meterologica,
In central
for
Ages,
antiquity
Aristotle
(Historia
A.D.)).
Description
of great
by
Seneca
as warnings
Middle
fears.
A
those
77
and
the
of aurora
are
340
(ca.
Introductory
unspeccalled
northern last
years
nuclear in
1958
(Cullington,
This
review
influenced few
by
years.
the
the geomagnetic
auroral
1951;
and
which
is largely
ellite
studies
detail,
the
spectrum,
phenomena,
The
determined
they
above.
Finally,
nomena
will be
results
obtained
of auroral
1955;
Chamberlain, to them
for
studies, will be
here
the geomagnetic particles in the
theoretical
discussed
are
in the
last
have
1961)
some
details
on,
correlations on
the
field.
will
which
phenomena
morphological
contained
proposed briefly
on
emphasis by
not
characteristics
is referred
auroral
are
and
reviews
St6rmer,
older
etc.
auroral
field
reader
of primary
since
on
extensive
(Harang,
recently,
other
concentrate
Excellent
appeared, fairly
will
also
with
morphology,
Rocket
be
e.g.,
and
treated
sat-
in some
extensivetreatisesmentioned
models
for
in relation
various
to the
auroral
phe-
observatio/is.
Z/ In this first teristics
i.
will
Intensity
subsection
be
given.
and
Energy
Aurora sky,
as
aurora
value).
the value The
majority
down
For
used:
Way;
provides These effort been
estimation four
equal
to place slightly
brightness equal
in terms
of aurora
by
for
intense
the than
to the full moon. the whole
visual
of the
is equal
at the
on
more
and
Brightness
Hunten
of number
emission IBC
scale by
weaker
International
extremely
IBC
even
in the
except
scale
exists.
to that of moonlit
the
charac-
phenomena 1960,
are
aurora
to that of thin moonlit
illumination are
luminous
fully comparable
however,
airglow
of an
modified
important
are
of brightness
definitions
of _-a'u_ral
Friedman,
auroras
They
are,
of the
classes
I, the
intense
1 (after
strongest i.
of auroras
a total
definitions most
very
in Table
II, brightness
brightness
of the most in Table
to the intensity
following are
The
given
description
Considerations
is one
is illustrated
a short
an
clouds; equivalent
absolute
(1955), of photons
in aurora)
to that of the
ground
Seaton
per
and
IV,
the
Milky III, aurora
to full moonlight. made
His
proposedO
ofk cm
clouds;
(1954)
basis.
who
the (IBC)
cirrus
cumulus
crude.
observers, Coefficient
a first
results
have
the following
5577A
(generally
2 (column)
and
I
i09
= 1 kR
II
101°
= i0 kR
III
1011
= i00
IV
1012
= 1000
kR kR
sec.
the
Table 1 Source
Flux (ergs cm -2 sec -1) 1.4
Sun
Full
moon
Strong
aurora
Total
starlight
Airglow
OH
(visible)
{infrared)
Lyman-=
• lO s
3000.
10 -3
1000"
10 -3
1.8
• 10 -3
16
• I0 "a
19
• 10 -3
I0
• i0 -3
0.I
" 10 -3
3.8
• I0 -3
o
Celestial
Cosmic
sources
rays
{1230-1350A)
106 photons/cm 2 (column) sec is called 1 Rayleigh (1R) in accordance with the proposal of Hunten et al. (1956). (For a discussion of the Rayleigh unit see also Chamberlain, 1961, Appendix II). The Rayleigh unit is not limited to a special wave length as is the IBC. The energy influx required to produce visible aurora has been measured (McIlwain, 1960; O'Brien and Taylor, 1964) and has also been computed from optical emissions (Omholt, 1959; Chamberlain, 1961). The results show reasonable agreement. 0.Z - I% of the input energy seems
to be
produce
converted
an
Hultqvist,
IBC
to visible
I aurora
1964c).
light.
is of the
The
order
Measurements
1964).
cylinder in the
average
density
of the
to the
upper
some
15%
of the
solar
beam
auroral
zones
1961;
drag
temperature
in the
auroral
equator
on
1964).
The
heating
auroral
zones
rienced
during
geomagnetically to be
these
and
4 or
It has
with been
emissions
of intensity
to include
emissions
fairly
Injun zone
the
be
energy
occasions much
radiated
energy
away
(only
1961).
It
atmosphere
particle
3 indicate
influx
that the
is essentially days
the
(Jacchia
and
perturbations
greater
in low
in (Bates,
than
the
upper same
as
Slowley, in the
heating
expe-
latitudes.
of Aurora
intensity
at least weaker
on
5 times
Classification
some
upper
the
geomagnetic
perturbations
In connection
by
disturbed
accompanying
seems
on
an
flux must and
contribute
of the
Thus
auroras
energy
thus
a
1963).
of the
at the
within
to Chamberlain,
determined
Maeda,
show
to be transformed
particles,
events
temperature
is primarily
e.g.
ergs/sec.
strong
unsufficient
according
that the
has
of this is probably
observations
atmosphere
Definition
auroral
wind
very
solar-plasma
be
to
(see
3 satellite
of 1020
energy
during
even
Most
Chamberlain,
considered.
may
solar
order
of precipitated
to heat
possible
Injun
of the
wind
relevant
Large
transformed
quite
solar
energy
1963).
flux
required 2 sec
to sustain auroras around (i011 watts) (O'Brien and
is of the
However,
atmosphere.
Recent
Z.
radii
of the
into kinetic
(Mogilevskiy,
1960b;
i%
fraction
converted
energy
earth
precipitation.
appreciable
the
average I0
about
into particle
seems
The
of radius
energy ergs/cm
by meansofthe
that the average energy input rate required the world is of the order of 1018 ergs/sec Taylor,
input
of a few
the
common a few
than
definition to mean
times
that.
4
the
From
of aurora by
aurora
airglow a physical
has
to be
sporadic
intensity point
but not of view
this is not a good definition. nisms of which are different, brightne ss.
Airglow and aurora, the production mechamay well be thought of as being of similar
A definition based on the mechanism of excitation would certainly be preferred. Along this line aurora
is often
defined
as
3914
nitrogen
emissions
band
in which
- which
the
intensity
is produced
by
collision
line at 5577 A is of the order less than unity. Unfortunately, are
complex
them
and
and
Roach
location phenomena subvisual Roach,
of which
of widely
geomagnetic
emissions,
different field.
Roach
the geographical
the geomagnetic
field.
include the stable red arcs, which in middle latitudes (see the review
auroral
(m
arcs),
by particles
aurora
is an
that occur
can
to Elvey,
extremely be
!.
Polar
Discrete
polar aurora
3.
High
Intermediate M-arcs
6.
Ordinary
red
polar
to several
type
of aurora
whole
cap
known
whether
they
or not.
phenomenon.
in the following
The
various
six classes,
for
instance
auroras
(St6rmer's
red
glow
arcs
i00
Mev,
discrete different
from
type
type
in the
give
rise
If)
I)
by
Sandford
energy to polar
cap
and has
a pronounced
activity
maximum.
The
and
cap
is often
auroras
ordinary
(1961b).
range
rare
caps
polar
III)
discovered
protons
which
fairly
at solar polar
was
solar
is thus
type
(St6rmer's
(St6rmer's
aurora
same
frequency
The
energy)
complex
grouped
displays
the
Mev
quite
it is not
low
glow
4. 5.
the
which
all emissions
1964)
2.
by
for
(of very
aurora
and
or the other by particles of energy well include the above mentioned medium-
arcs
as
The
are mostly by Roach
review
red
consider
to use
in one way we will also
The
are
by
it impractical
to be
the as
atom
will in this
produced
over
aurora
the oxygen
We
The
rence
defined
makes
seems
aurora:
is determined
then also and located
produced
types
have
for
- and
_
In airglow it is usually much the excitation mechanisn_s
which
parameter and
the
are produced thermal and
latitude are
(1963)
1963).
which above
One
for airglow
between
excitation
of unity. however,
not well-known,
in definitions.
importance
(due
are
ratio
and emission
glow
from
It is some
i0
absorption. maximum
This of occur-
is distributed
subvisual.
have
several
auroral-zone
characteristics aurora
(St_rrner's
which type
I).
Their
occurrence
and
they
frequency
also
spectrum
show
is,
however,
Class No. latitudes butit
The
arcs
The
average
the values
for
ordinary
from
name).
The
For
so-called type
them.
Notonly
takes
place
and
Such
3.
we
in the
zones The
mostly
slowly
"band." a great and
then
so
begin from
its regular are
very
" waving
irregular
forms
therespectro-
the most
deal
mainly
emission
and
with
also 1961)
Pope,
and
1960,
1960).
auroral
phenomena
also
the
effect
UHF
on
not
so-called
radio
the propagation
frequency
ranges,
with
of a special
the
by
the
excitation.
type.
enormous
variety
in their
talk
typical
sequences
about
with
1963d). a glow
relatively Suddenly across bow
long,
the
shape the band
like a curtain may
but
to the
of light
south.
to appear
to
is between
Chamberlain,
the horizon
bows
or
aurora
but
Akasofu,
remain
north
to lose
"drapery,
may
begin
If the rays
fading
however,
rises
by far,
simultaneously
an
1954, may
due
Display
show
can,
grey
aurora;
will
the
echoes
in low
prominent
Murcray
and
look
review
radiation refers
The
type
(which
Helliwell,
among
produced
displays
"arc"
"rays"
to fold and
and
homogeneous
towards
and
1958,
Martin
high
displays.
red
most
are,
the
at
(1955).
instance
Hartz,
to radio
Heppner,
glow An
by
for
in the VHF
the display
quiet
there
and
rise
One
horizon.
ing
(see
of an Auroral
auroral
(see e.g.
east-west.
of this
atmosphere gives
is the
displays
rest
km
high
StSrmer
auroral
radio-aurora
ral development.
and
line see
will include
Development
auroral
_
often
is 196 and
the
(cf e.g.
especially
ionization
events
then activity.
auroral
They
limit
light is emitted
1961,
term
The
activity
magnetic
ordinary
displays
of electromagnetic
The
The
solar
rare.
height
6300
and
visual
waves,
ionization
of
very
details
in the ultraviolet
emissions
aurora.
red
ordinary
Peterson
of radio
low with
that
auroral
of aurora
In this review only
are
more
at radio-frequencies Egan
to
lower
The
feature.
common
at
3 - high red aurora - is the most common also occurs in the auroral zone sometimes.
intermediate
their
higher correlation
similar
faintness.
scopic
is
a negative
appear
and
the
forms
it may arc. and
one
for
arc
to form
assumes sky.
disappear
an
or more
approximately hours,
brighten The
of of the
poleward
oriented
quiescent
in the and
Equatorward
along
(arc),
tempo-
drift-
here is then
and likely
irregular
the appearance Rapidly all over
of
moving the
sky.
As the display dies down, waves of light may surge upwards from the horizon in quick succession causing existing auroral forms to brighten as the waves pass over them (flaming aurora). A continuous glow (veil) may extend over a large part of the sky, serving sometimes as a background to the active forms. At other times, diffuse patches of light, closely may
resembling
come
There
and
is a tendency
phase.
The
of the
and
This
Auroral
Union
St6rmer
and
The
Committee
of the scheme
i.
ous
b) and
for
arch
are
to be
forms
i.i. Band-like border.
(Fig. an
I.i) arc
These
3.
sets
diffuse with
surface
sequence On
the
is poleward
the development For
instance
some
in.
the details
is quite
good
Stormer
descrip-
(1955).
or folds
These
are
or part
recommendations
described
in detail
"International
for Jacka
have mostly been classiof 1930 of the International
Quiet
Sun
Year"
de G_ophysique" describing and
in terms
worked
in his book
(IQSY),
(CIG)
auroras.
Paton
were
also
has
It will
(Fig.
1964-
adopted be
briefly
(1963).
of 4 parameters
(6 if brightness
included).
are
divided
forms:
into three
These
the form of an
arch,
are
appears with
groups
characterized
as
a simple,
a regular
lower
by
a continu-
slightly border
curving it is
(A).
(ii) When kinks
the
following
(i) When called
the
described
caps
see for
International
is described
also
Auroral
lower
polar
sky.
mentioned.
in section
events,
of nomenclature
aurora
color
as
Geophysics.
"Comit_
below,
An and
The
auroral
discussed
after
correlated
disturbance. zone,
in the
until twilight
into arcs is closely
decades the auroral forms with the recommendations
(1930a,
1955).
reviewed
there
Forms
(StSrmer,
new
and
pulsations,
the central
auroral
of Geodesy
1965,
over
will be
In the last few fied in accordance
.out by
pattern
of the
of individual
here
regular
reformation
magnetic
especially
different. tions
for
equatorward
side,
appear
with
development
coincident
typical
4.
clouds,
go,often
the lower
1.2-) the form
border is called
is irregular a band
(B).
and
contains
a
1.2. or a veil (V).
Diffuse forms:
These may take the form of a patch (P)
(i) The patch is simply a blob of illumination boundary; it often resembles an isolated cloud.
ill-defined
with an
(ii) The veil refers to the uniform luminosity that may cover alarge part of the sky. It may occur alone or as a background to other forms. 1.3. Rays (R): These are shafts of light aligned in the direction of the earth's magnetic field (cf. Fig. 1.3). There may be a single ray, a bundle of rays close together or many scattered rays (subscripts i, Z, 3 may be added to R to indicate short, medium, and long rays respectively). 2. Structure is described by the following
three adjectives
2.1. Homogeneous (H): This term implies an apparent lack of internal structure in the form. The brightness is uniform or it changes only gradually across the form. A homogeneous arc (HA), and horseshoe-shaped bands are shown in Fig. 1.4. 2.Z. Striated (S): The form contains rather irregular striations or filaments aligned roughly parallel with the lower border (Fig. 1.5). Striation is usually recognizable only when the form is nearly overhead. 2.3. Rayed (R): ance within them of rays the
geomagnetic
3. may,
field (Fig.
Qualifying
when
two
numeral
closely
3.Z. of an arc
or
be
Multiple
associated
script
and
situated
One
This
of three
term
parallel actual
homogeneous
Fragmentary
along
the
by the appear-
lines
of force
of
qualifying
parameters
to the description.
roughly the
aligned
1.6).
added
(m):
indicates
band
are
parameters:
relevant,
3.1. more
Rayed forms are characterized which
is used forms
number
when
of the
there same
of forms,
occur kind.
e.g.
two (A
m2HB
subsignifies
bands).
(f): This
is present.
8
term
is used
when
only
or
a portion
3.3. tion
Coronal
of the lines
geneous they
forms
pass 4.
(c):
of magnetic may
over
When
also
the
force
present
magnetic
Condition
any
rayed
form
the rays a similar
is
viewed
in
appear
to converge.
coronal
appearance
the
direcHomo-
where
zenith.
describes
the
behavior
of
a form
or
of
the
whole
display.
4.1. in
Quiet
position
or
4.Z.
(a):
forms
are
Such
along
(i) boundary
(ii) border the
of
of
form
undergoes
a form
which
only
very
slow
changes
a form
is
frequently
a 1 of
- refers a band.
to
a 2
-
to
while
refers the
the
or
movement
the
form
moves
changes
its
shape
bright.
rapid
itself
of
folds
change
may
also
of
or
irregularities
shape
move
of
the
rapidly
lower
across
sky.
(iii) horizontally
rays
fade
rather
other
parts
often
ation
a 3
- indicates along a form.
(iv) quickly,
a 4
of
sky.
the
4.3. and
range
a large
ing
upwards
very
rapid by
flickering
(p):
from
in
to
this in
a fraction
Pl
a variation forms.
the
occurrence
a display similar or
A photograph
fluctuation
(i)
over
- refers while new,
Pulsing
rythmic
may
display out the
up
The
Active
rapidly.
the
(q):
shape.
-
pulsating
of
an
a second
forms: the
event
The to
is
The phase
of period
the
which
seen
in
rapid
of
fluctu-
of
the
minutes.
form is
Fig.
fairly
order
affected of
movement
in which forms forms appear in
a condition
brightness.
brightness,
a rapid
as a whole different
such
describes of
of
or
uniform
forms through-
(ii) area
P2 - flaming aurora. This kind of pulsing extends of the sky which appears lit by surges of light sweep-
over
it.
and
(iii) P3 more or flames.
flickering: less irregular This
A large part changes
occurs
only
9
rarely.
of in
the display brightness
as
undergoes if lit
1.7.
(iv)
P4 -
that progresses
rapidly
Most
can
or
auroras
sometimes (f)
' are form
ness see
by in
and
color
Jacka
and
very
during reported arcs zenithal
an average was found
.other
hand,
be
or
as
narrow
is
greater
at
acitivity
Roach,
symbols-
of
medium
length
for
the
form
(as) the bright-
(for
details
the
m
was
a few
a
solar
cycle
and
again, have
It
has
been
(Elvey,
1957).
been
measured diurnal
of
found
to
the
arcs
vary
with
atmospheric When
auroras
often
extension
to
heights-the
red
discovered
thickthe
On
significant
the
great
km
The
has
No
of
18.2
1963). activity.
extension
and
the
thickness
and
thickness
smaller
cameras,
the
3.5
have
values
recording
Volkman, magnetic
vertical
kin.
being
increase
of
aurora km
The of
1961).
The
ten
net
the
(Akasofu,
found.
extension
4000-5000
between
curtain
thinness of
1963).
measurements
(Kim and increasing
auroral
lengths the
varying
characterized
recordings
of of
are
a remarkable
Akasofu,
coverage
km with
150-350
of
arcs
values 9.1
and
photographic
Recent
given
zones
depth
the
appear
sunspot less red
deep auroras
stable
midlatitude
may
occur
in complete
arcs,
by
auroral arcs. and in height. rings
around
They Present
Barbier
(1958),
cover some evidence
the world
hunsuggests
(cf. Roach
and
1963).
The
rays
are
characterized
length has been extensively to several hundred krn, but
found
are
auroral
1962,
completely from ordinary of kilometers in latitude
that they
150
four
a S cfR2Bsignifies
rays
direction
auroral
active
end to
instance
symbol
the
the
longer.
an
at
al.,
by
have
the the
by
forms.
A.
The differ dreds
east-west
et
still
atmosphere
of type
in
generally
starts
the
bands
limited
as
activity,
the
From
variation
bands
solar
For
after
and
value of to increase
for
seasonal
and
in
be
described
whose
of brightness
of homogenous
a horizontal direction along the form magnetic zenith. Symbols indicating
continuous
arcs
variation
extent
1963).
extension
may
well
(R2B)
added
arcs
were
so
be
(Feldstein
mentioned 40
in the
Paton,
IGY
fairly
band
direction.
been
irregular
horizontal
subindices.
may
long
An
the
be
a rayed
auroral
made
to
of
north-south
with ness
thus
moving rapidly a corona in
The
along
five-with
a fragment (R2) and
streaming:
kin.
Especially
to extend
of the order
up
the to ii00
of 1 krn (see
by
studied a more
sunlit km e.g.
rays
great
and
thinness.
The
by St_rmer (1955). It may amount common value is between i00 and can
sometimes. the
length
recent
I0
be
very The study
long
and
diameter of Akasofu,
have
been
of the
rays
1963b).
is
Wilcke mately (1920)
(1777)
along found
first
the that
noticed
that
great
to be
due
to the
would have to be at about StSrmer (1938) found the sky.
Abbott
(1958)
disturbed
7 or
8 ° lower
rays
field
showed
than
the
of the
a rate
aligned
approxi-
Vegard and Krogness point," i.e. the point
field
1000 km to show a one auroral zenith to wander
measured
are
appear to converge, the magnetic zenith.
curvature
at least 1° in 5 minutes of time. side of the normal (undisturbed) the
auroral
earth's magnetic field lines. the elevation of the "radiant
towards which the rays in a corona cally one degree or so lower than is too
the
of motion
is systematiThis difference
lines.
(The
degree around
for
the
rays
displacement). a little in the
radiant
point
The radiant point was found on magnetic zenith, but measurements
that
the
radiant
instantaneous
point.
No
magnetic
relationship
of either of
zenith
between
was the
motions
of the magnetic zenith and the auroral zenith was found. Cole (1963) has studied in detail the geometry of the radiant point and found that commonly him
as
differs the
by
0.5
direction
a straight amount
line, passing to as much as
auroral oriented
zenith along
about
at auroral in other
heights, ways.
Detailed forms
auroral
normally Dark about the
the
studies seen
detailed
direction
is
have rayed
There
is
in time.
Rapid
observed Campbell
and and
(1962),
shown to the
teristics berlain
a more of various (1961).
a segment
difference of the
with
width They
(Nadubovich
is several
in aurora in auroral
detailed auroral
Berger review forms,
field
accuracy
exist not only but also in what and
only
emission
(1963),
see
11
lines
Starkov,
in is
1961). length often
of in
often
also
minutes.
not
of older
of
rays are valuable
of 150 m and an average have been observed most
Campbell (1960a,b), (1961), Iyengar and
(1962),
the give
by
may local
comparable
that fine structures eye or the camera
duration
variations by
defined
as
geomagnetic
to obtain
forms
structure
studied Leinbach
Skrynnikov For
The
a fine
zenith,"
regarded
of the
difficult
homogeneous
hours.
auroral
ray,
the observer. The degrees. Observations
filaments of a minimum Z0 km have been found. morning
"local
yet been reported. Presuming lines such observations would
which
called
the
through several
have not the field
information
° from
of a (hypothetical)
it
and
in space rate
recently
Campbell and Shepherd(1961), Gustafsson
investigations e.g.
have
but
StSrmer
been
Rees (1961, Omholt (1964).
of the (1955)
characand
Chain=
5.
Emission
Spectrum
But will not be Bates
for
a very
dealt
with
(1960)
The colour
and
brief
introductory
in this review.
Chamberlain
aurora
seen
survey,
For
the
auroral
a detailed
spectrum
review
see
e.g.
(1961).
in high
is due to a forbidden
latitudes
is usually
transitition
(_S_°D)
green
to the
in the
oxygen
eye.
The
atom.
O
The the
wavelength eye.
time
is 5577A,
The
of the
excited
In lower
nomenclature
6364,
6391
5577Aline.
excited
level
of about
in active
the excitation
There exist emission.
1958.
6300
sec for
Most
and
to be
red
forbidden
with
1960).
Due
1955).
(high
red
is then
in cascade
aurora
the
(ID---3P)
a lifetime
6300,
after
of the
to the long
it is therefore
of
to a life-
Harang,
characteristic
this line and
as
lifetime,
mostly
seen
these
lines
are
emitted
for
some
time
ceased.
auroras even One famous
other
seen
is produced
(Omholt,
sensitivity
corresponding
The long lives of the metastable levels 6300A lines are emitted give rise to colour
auroras
auroral
the boundaries
maximum
low
(Omholt
spectral
which
line is also
if0
has
sec
is often
The
of O,
to the
is very 3/4
aurora
at high altitudes. the k 5577A and_
variations
which
the
is important
in auroras from which
6300A
of about
used). The
deactivation
after
level
A triplett
is close
probability
latitudes
in the the
which
transition
in high example
spectra
are,
latitudes with anomalously increased of this was the one on II Feb.
belong
however,
to one
not
very
of three
sharp
types,
between
(Krasovskii,
1961).
The first type is the low-latitude spectrum mentioned above, in which the ratio of the intensities of the 6300A and 5577 A lines is high, and where
these
two
molecule
bands.
dominate
but
cules
are
emissions In the next
in addition
seen.
This
latitudes.
Finally,
molecular
bands.
of atomic systems most
oxygen
frequently are
exciting
agent
to the third
type,
emissions
type
type
appears
apparently into the
in high
atmosphere,
e.g.
and
and
is characterized
second
latitudes. for
by
the
type.
IZ
This
The the
depth
and
high
the
type
from
low
intense line
band of spectrum
between
of penetration
increasing
moleand
green
negative
third
difference
depth
atoms
nitrogen
numerous
spectra
positive
detail.
ionized
in both by
in such
the nitrogen
neutral
is observed
in great
accounted
over
of neutral
that
the first and
correlated
lines
of spectrum
the third
and
dominate of ionized
It is remarkable
ofN 2 are
spectra
strongly
the of the
the first
Auroras located at great atmospheric depths usually have a red lower border (red aurora of type B). This is due mainly to the first positive bandsystem of the neutral nitrogen molecule. The reason for the domination of the N2 emissions at great depths is probably that the 'S level
of Ol
The
is deactivated
sunlit
auroras
auroras
located
color
which
by
have
in the
dark
is produced
by
collisions
to
a spectrum
an
appreciable
different
atmosphere.
They
re.sonance
from
have
emission
amount.
that of the
a bluish-white
of primarily
the first +
negative
Of
band-system
special
first found
by
that protons 4000
interest Vegard
are
km/sec
forms.
entering
appearance
others).
Auroras
impact
certain
at least
one
aurora,
for which
alone
{Omholt
more are
is often
(Stoffregen
and
Chamberlain
seen
field.
stable
feature
location
than
of these
They
are
196Z).
For
arcs
namely
red
the
details
and
Galperin
arcs,
6300
_
mentioned line has
is definitely
lined
up
along
tion without
any
low
energy
(1964),
spectroscopic
the excitation
particles.
On
the
may
be
how
the magnetic
Megill
have
proposed
and
Carleton
responsible
excitation
for
mechanisms
(1964)
the excitation. are
reviewed
by
13
Roach
emission A distinct main
the
forms
reviews
no
of
other
identified.
of circles
from
the
along the geomagnetic by collision excitaexcited. effect
According caused
excitation
field control
comes
in.
fields
proposals
Roach
by
is chemical
electric
of other and
It the
the geomagnetic
that local
Anumber
the
clearly by
being
if the
it is difficult to understand
be
been
a heating
hand,
of
(1963).
surface produced
features
other
see
it
contributors.
to the eye. started, on
and
projections
equatorial plane to the earth's It is not clear how they can be
to Dalgarno
case
types
earlier,
controlled
geomagnetic field lines.
other
aurora
more
Krasovskii(1961)
In the midlatitude
The
the proton
been
relatively,
energy
invisible this has
strong
have
After midnight no hydrogen but rather north of these.
between
Derblom,
(1961),
spectroscopic
in other
main
and so
In any
energy
glow is barely visible or even the electron aurora and, when
dark
might
1962).
than
to
preced-
1958,
supplied,
the
up
line was
the protons
certainly
of it before midnight. south of auroral forms
Elvey,
theHa
et al.
were
showed
observed
that this aurora
auroras
of magnitude
They
I ,
in homogeneous
been
and
in which
(N 2
velocities
mostly has
(Romick
emissions
electrons
seen
molecule
line contour with
glow
observed
equator side is observed region
are
auroras
that in those
order
emissions.
atmosphere
They
been
by proton
appears
line
of their
hydrogen
of bright spectral
nitrogen
hydrogen
upper
weak
have
charged
Analysis
1951).
to other
The hydrogen occurs before
the
the
recently,
ing the
produced
are (1939).
(Meinel,
More
compared
of the positively
(1963).
for
may
6.
Methods
of
Recording
Almost by
visual
all data
observers
sky-cameras, was
by
up
(1957)
and
detailed Fig. white
(1947),
Davis
and
the
Studies
During
IGY
net
the whole
sky
a large
(see
have
(1955),
Elvey
been
every
all-
minute, and
(1955),
Stoffregen,
set of allsky-camera
taken
constructed
Stoffregen
and
was
of so called
automatically
allsky-cameras
A
allsky Soviet
Morphological of aurora
Lebedinskii
Elvey
description).
1.8. Most film. The
for
morphology
to IGY.
Various
Gartlein
Aurora
concerning
photographing
in operation.
used
Visual
Park
1957,
for
are
shown
pictures
films taken hitherto have been 16ram and Canadian cameras used, however,
a in
black and 35mm
film. In the last few years and Heiser, 1959; Gadsden,
color film has begun to be used (Sand.ford 1960; Sandford, 1961). The committee for
the
"International
Year,"
the
use
of 35
detailed net
Quiet
mm
synoptic
bilities are
has
devices and
(Elvey
Davis,
and
The
in (b)
The
(c) moving
model
observed,
(1960)
They
and
the
the possi-
IGY
records of the
satellites, auroral
films
have
regions.
been
construc-
1961).
have
made
them
with
arrived
that
solution
altitude
caps
Kaneda,
comparing
the
For
IGY.
regions
from to the
high
polar
aurora.
during
of the polar
very
recommended
desirable
it was
patterns
and
allsky-camera
as in
well)
was
detection very
at
and
eye
more
is
If the
observations in the
that
operated slightly
of
weak
allsky-camera
forms. his
by
than
allsky-camera
Nagata
Leinbach
locating
The
allsky-camera be
US
detecting
accurately
sky,
and
types
observer
equal
analyzing
of the
an
evaluation
of
simultaneous the
all-
visual
following
conclusions,
s.
other
visual
of the
observations.
other (a)
most
by
most
1957;
has
contribution
be given
for
of CIG details it is highly
part
synoptic
may
Belon,
photometric
most
important
observations
among
areas
showing
Deehr,
sky-camera
more
in the future
scale
most
problem
Automatic
large
that for
A
photographs
ted
over
large
1964-65,
provides
denser
shown
limited.
morphology taking
will be
of obtaining
very
which
studies
of cameras
Experience
Sun
film,
very
but
less weak
well
able
to
observer
see were
would,
in
small
region.
allsky-camera
shape
the to
general,
is
14
forms
to the
and
visual
of most
details
of
watch
only
be
superior
However,
if
superior
(and an
probably
experienced is
about
forms.
superior the
IGY than
diffused
defined
is much recording
during sensitive
in
the
observer
auroral
very a
bright small to
the
sense
or part
those
entire
(b)
fastof
of sky
of
in
forms.
the
the is
above.
to
(d) A greater degree of continuity in auroral forms is often indicated in the compressed image of the sky on all-sky photographs than is apparent to the visual observer. (e) During the times when visual observers report pulsating aurora, the over-all appearance of the display seems to be quite distinctive and often readily identified on the allsky film. The around
exposure
Z0
possible
to
studies
of
than
has
time
sec.
By
take two
to
earlier was
used
(Davis
and
Hicks,
It
has
recently
three
the of
auroral
aurora
(Noxon,
of
means
pictures orders
been
ordinary
intensifier Z4
of
possible.
successfully
allsky-cameras
image
times
for
TV
a second.
magnitude An
is and
Such
more
instrument
the first time
generally
camera
rapid for
time
rapid
in the
it films
variations
filming
autumn
is allow
of of 1963
1963).
become
possible
to
1963).
15
observe
visual
aurora
in
daytime
Figure Fig.
l.l-Auroral
Fig.
1.2-A
Fig.
1.3-Auroral
Captions
arc
band
rays
Z4 pictures
photographed per
Fig.
1.4-Homogeneous
Fig.
1.5-Striated
Fig.
1.6-Rayed
Fig.
1.7-Photograph
sec.
with (Courtesy
auroral auroral
arc
and
an
exposure
time
T.
N.
and
Davis
of
1/60
G.
T.
sec, Hicks).
bands
arc
bands
rapidly
of an
and
new
active forms
aurora. appear
The
forms
move
continuously
and
in other
fade
parts
of
the sky.
Fig.
1.8-Allsky
camera
(Courtesy
Comment: tional
Atlas
Geodetic
Atlas," Year -
"Physics
and
prepared of
the of
to
Figs.
of
Auroral
by
the
at
Kiruna
and
4-7
Forms,
on
Z9
Jan.
Committee
Z, and
4,
Oslo
for de
and
6
airglow."
16
-
can
be
taken
" published
Union,
International Figs.
aurora
1-Z
Geophysical
"Comit_
concerning
taken
1957
Stoffregen)
Alternatives
"Photographic
or
pictures
W.
the
1957
or
International
G_ophysique," from
from
by
Chamberlain's
either
the the
Interna"Auroral Quiet
Edinburgh book
Sun 1963.
~
~~
F i g . 1.1 - A u r o r a l a r c
Fig. 1 .2 -A band
Fig. 1.3-Auroral rays photographed with an exposure time of 1 / 6 0 s e c , 2 4 pictures per sec. (Courtesy T. N. Davis and G. T . Hicks).
Fig. 1.4-Homogeneous a u r o r a l a r c and bands
F i g . 1.5-Striated a u r o r a l a r c
Fig. 1.6 -Rayed bands
F i g . 1.7-Photograph of a n active a u r o r a . The f o r m s move and fade rapidly and n e w forms appear continuously in other p a r t s of the sky.
2.
I.
Geographical (a)
poles
The
Distribution
the
auroral
seems
Loomis
on
(1860,
aurora
Fritz's
the night
in USA
originating
at any
was
maximal.
geographical
equal
of night
It has
statistical
as
has
become
having
review, is
equaled
of
a particular
the
or
use
the
distance
zone
over about from
will of
a period variation one
night
to
by
between of be
overhead
the
several
of
the
to
as
points
that
as
months.
location as
of is
at
the
often
17
this
auroral done
isoau-
the
auroral
zone
width. the
there by
the
through literature.
the is
peak
of
max-
observations
definition zone
in
this zone
amplitude of
which
In
auroral
position
determined
With
points
called
half-maximum
The
position
(1953)
are
of of
of
is thus
in evaluating
variable,
of
zone
connecting
width
of
curve part
Chapman
zenith
think
and the
activity.
auroras,
of
another,
years which
auroral
taken
"Lines
the part
The in any
auroral by
in the
of the
any
overhead
of
from
where
width.
The
1881) amount
1878,
during
aurora
aurora
unspecified
definition
no
studied
1874,
of points
recommended
recent
was
location
sky
of seeing
curves.
(1837).
to about
of the
of the
towards
of a large
the locus
part
occurrence
generally
the
measure
occurrence
taken talk
to
auroral
imum
but
will
1873,
up
map
of seeing
in
(1868,
isochasm.
distribution
customary
a finite, we
an
Muncke latitude
analysis
a line, having
been
the probability
by on
times
as
probability
is called
first
Fritz
old
in any
of equal probability of auroral total lines or isoaurores.
It
by
defined
It is thus
with
to use
and
very
aurora
continuously
frequency
the first detailed
isochasm.
others
in print
from
an
the maximum
increase
a detailed
zone
time
not
made
auroral
points
does
noted
of seeing was
connecting
and
Aurora
Activity
occurrence
(1881)
could delineate auroral zone.
probability
sky
1868)
Fritz
which he northern
been
of auroral
in Germany. data
of Auroral
activity
to have
dependence
by
of Visual
Introduction
That the
Morphology
we
cannot one
night One
is
then
using
the
notation
auroral
zone
for
at a given moment of time. Below, "zone" or "momentaneous auroral this unique-time Both highly
the width
dependent
commonly
account
in this measure. defined
each
similar
determined
a
1 ° latitude
following
is widely
geomagnetic
and
S.
the
The
are
on
the
regions,
called
(b)
the
{1944)
modification
termined taken
by
at 39 Arctic
during
While tematic about
1878,
particularly delineations, periods
zone
of it are
shown
the
is not
employed
taken
auroral
borders
appear-
borders
at 5-minute
station.
It gives
auroral
and
south)
belt
auroral
side
(Jacka
suggested
and
subauroral
auroral
polar
belts
zones
zones
zones
and
from
45 ° N
and
the
au-
Alternatively, are
named
cover
Paton,
Chap-
between
between
zones).
which
by
extend
the
cispolar
cap,
1963).
latitudinal
activity
delineation
of Fritz
(1881)
in Fig.
2. 1 together
basis
of photographic
on the
and
the
of the
auroral
auroral
visual
zone
observations
Vestine
had
those from however,
of time
most activity,
observations
with
made
and
Vestine's
a zone
de-
recordings at three
sites
1957-58.
Fritz's
auroral
of the
(1960)
{north
auroral
regions
stations
the IGY,
is
(or full-hour) total number of
lower
the
the
the
auroral
Feldstein
also
the minauroral
include
on
of visual
northern
The
aurora
lower
zone
of auroral
geography,
regions
and
side
those
locations
the through
auroral
within
transauroral
a,b)
to the poles;
regions
equatorial
distribution
The
on
auroral
regions
while
Observed
counting
or for
distributions.
(_m) 60°
auroral
of the
of auroral
passing
latitude;
(the polar
regions
auroral
by
The
latitudes
caps
{1962
terminology
used.
60 ° magnetic
450
Davis
band
sharper
45 ° and
roral
employed.
frequency
intensity
the total number
but somewhat
The man,
by
hour-as
intervals-in
of the auroral
of activity-measure
The
exists
activity.
center
is the occurrence
intervals.
aurora
precipitation area" zone" will be used
auroral
of the
in which
as the ratio of the number of half-hour aurora could be seen overhead to the
full-) hour
incidence,
of visual
type
area
"auroral occurrence
the location
measure
defined in which
half-(or
ing
and
on the
used
generally intervals
into
distribution
the
with
at his
was
from
based
almost
several
disposal
more
hundred
entirely
on unsys-
years
systematic
B.C.
up
observations,
the two polar years 188Z-3 and 1932-3. are based on material obtained over very
secularly
changing
18
geomagnetic
to
field,
varying
Both long solar
activity,
partly unknown meteorological
Feldstein's curve is based the use of a fairly uniform employed used, as
conditions,
etc.
In contrast,
on observations made within a few years with technique at all stations. The auroral indices
in his determination are more accurate than those only the aurora in the zenith has been utilized.
The
greatest
auroral
zones
Feldstein's
The
difference
is in the
curve
first
between
region
reaches
attempt
Vestine's
of Hudson
about
Bay,
4 ° farther
to investigate
and
Feldstein's
in North
south
northern
America,
than
the auroral
previously
where
Vestine's.
statistics
in the
southern
hemisphere was made by Boller (1898). White and Geddes (1939) estimated the location of the zone on the basis of scattered visual observations
of aurora
based are
on
australis,
geomagnetic
shown
and
Vestine
observations
in Fig.
2.2
together
with
Feldstein's (1960) zones. The at 20 stations on the Antarctic
and
Snyder
Bond's
and
IGY material continent and
recent
rence
study
frequency
in time
to the
auroral
forms,
ords
taken
and
of the detailed
is that of Davis solar
activity
as defined
in Alaska
in northern
Canada incidence
in connecting stations.
the
The tude
curve
latitude. The
The
hourly
tween imum.
60
data
width for
occurrence and
Already
auroral
and
Solomatina
the
zenith
atom=
zone,
during
with
IGY
zone,
was
by
55%
spread
above,
of rec-
than for
69 ° ) the points involved
Canadian
(1962
on
Fig.
of auroral
inner
bemax-
side
of
Feldstein
occurrence
quiet index with
one.
activity
the
2.3).
6 ° in
a) to be
at solar
to I0%0, while
on magnetically
lati-
is about
is a relative
Davis
latitude
on disturbed days in the auroral zones. The the ratio of the number of half-hour intervals
19
It refers
allsky-camera
2.3
(c.f.
occur-
67 ° geomagnetic
defined
that the frequency about
2.3.
to the ,.uncertainty
in Fig.
slower
was taken islands
"incidence"
era' less
66 ° and as
and
evaluation
of the high-latitude
found
down
was
The
from
zones
of auroral
in Fig.
indicated
is due
66 ° geomagnetic
60 ° it was
was
The
between
frequency
found
shown
latitude,
those
in the
1957-58.
a zone
two
(1960)
variation
deduced
"incidence"
the decrease
(1963)
was
latitude
of the
the
70%0 at about
the
90% was
scale
in
(for Cm > 69°).
its maximum
The
b),
geomagnetic
at high
Alaskan
has
in Alaska.
above,
(for the
representing
(1962
Jacka's
employed
latitudinal
maximum
defined
These
used by Feldstein at two stations on
situated south of Australia. The technique was similar to that used in the Arctic.
A
(1945)
in the Antarctic.
days
and
in about
of activity used auroras in the
zenith
to the total number
corded
in the form
found
that the
auroral
auroral
While
Jacka
of aurora points
at College
tween
the general
conjugate
area
between good
auroral
in USA,
detailed
Island
in the
northern
conjugate DeWitt
areas.
was
quoted
usually
certainly
above.
occur
as has
long
as
and
pairs
suspected.
for
at either
More
Island
and
the
observed of luminos-
and
and
MacQuaire
Kozebue
to be
of the
in the
simultaneous points
other
probable
end
be-
station
(1962)
observation
most
conjugate
correlation
of variation
found
any
therefore
occurrence
nearly
DeWitt
at Farewell was
years consistant.
(if at all significant)
and
of the
than
are
Antarctic
areas,
motion
auroras
better
It seems
austral
between
not the
reported
at Campbell
conjugacy
conjugate
been
and
observed
The
which
correlation
in the two
of the
however,
at Ellsworth
hemisphere
Breakup
realso
and
relations
between
(1960)
small
of form
events
southern
one.
Island,
activity
correlation auroral
boreal
in the last few
are,
correlation
Fillius
but very
pictures
but
They
any
and
in the
the detailed
hemispheres,
MacQuaire
kin),
the detailed
ity between
tions
and
600-700
about
appeared.
did not find
as
investigators
same.
ICY
in the two
of observation,
last mentioned occurrence
the
before
this have
(1961)
(off by
closely
known
on
intervals
The
of auroral
very
phenomena results
by
are
was
some
the
probability
zones
Nothing
of half-hour
of ascaplots.
two
investiga-
that auroras
of geomagnetic
observational
in
employed
data
field lines,
would
be
of great
value.
The
occurrence
tropical)
of aurora
is extremely
rare.
in very Even
low
latitudes
in central
(subtropical
Europe
and
the probability of seeing aurora is only a few thousandths center of the auroral zone. instead, these medium and auroras recorded tions by
of auroras
Schove
auroras by
are generally very spectacular also in ancient times. Recent extending
(1955),
Chapman
(c)
1957
are
(1956) low
and
latitudes
c), Abbott
(1951),
and
have
(1957
been
USA
of that at the low latitude
often been noted and of older observa-
region
Chapman have
southern
been
a, b).
described
Abbott
and
made Several
rather
of observational curves
good
equatorial
reasons plane
for
auroral
zones
postulating
outside
the
ZO
earth's
with
circular surface
fully
Chapman
of red auroral arcs occurring rather regularly will be discussed later in this chapter.
Comparison theoretical
There geomagnetic
at very
(1953,
(1959 a). A type auroral latitudes
into the minauroral
Matsushita
occurring
and have summaries
and
in sub-
various
symmetry of
distance
in
the
parameters representing ables of those processes, associated auroral
with
the
and
range
and
process
earth.
It follows
auroral
seems
physically
of a great
the
and
be
that introduced
field
different
from
the
line which
real
and
in the
According
phere
the
along
only
ion moves
assumption the seems
The along
purposes are used
projections the
real
of circles
geomagnetic the
may
distance
be
plane
same
in the
in one
quite of that
place
as
earth's
hemisphere one
in the
plane
to one
some
surface
founded.
is that an
of the auroral defined No
by
other
at-
will other
electron
hemis-
zones
or
an
along
field lines.
details
in the equatorial were
calculated
plane by
Such
of the actual
experimental
isochasms.
with
the
of Mc!lwain
method
L
curves
consisting
21
of integration
to the
Hultqvist
with
identical
a perturbation
a
earth's
involved.
field lines,
of comparison
practically
on
to be well are
at the
corresponding
in the foregoing
equatorial
an
face
configuration
of the
made
field line or
processes
if the
processes
on
will
field from
equatorial
surface
auroral
time,
field lines.
a geomagnetic assumption
the
the
points
plane.
the
projection
geomagnetic
from
earth's
the
equatorial
to this view to the
physical
the
with
as
of e.g.
the
place
and
lines,
at fixed
near
on
plane
field
If that is so, takes
equato-
meridians
magnetic
even
directions
distance
equatorial
at and
the
influenced
dependence
earth's
plane
the
The
magnetic
regions.
intersection
be
to geomagnetic
be true,
in its outer
intersects
correspond
The
should
field line connecting
mosphere
of the
two
Thus
average
observed
regard
in the equatorial
that of the
same
in the real
is appreciable
here
will not
longitudinal
with
from
disregarded.
locations,
deviation
distorted
the process
dipole
the
said
at which
only
radii
all geomagnetic
by the
the
of the different
in the
processes
auroral
deviation
been
is heavily
the
from
near
contribution
symmetric.
plane
are
seen
connected
distributed
by
This
has
time
many
equally
dipole field. surface.
What
are
earth
effects
axes
be
plausible-the
averages earth
rotation
that-if
zones
of several
minor
will therefore geomagnetic
in or
a measurable
equatorial
provided the
phenomena
field is circularly
geomagnetic
rotation,
at a given
in the
at a distance the dipole
in the
geomagnetic
plane
the dipole
plane
earth's
of the
the
field affords
surface,
configuration
rial
of auroral
Only
equatorial
earth's
by
the occurrence
zones.
in the
statistical averages for corresponding variin and near the equatorial plane, which are
The
earth's (1958)
projections
{1961). along
surfor
Hultqvist
the dipole
line
of the deflection line due to the harmonic
from effect
a dipole field line of the higher of the second to the fifth terms
development
yielded
deflection
of the vectors
for
gave the deflection for the mation field line-coinciding torial
plane
from
the The
well
outside
a large
earth's
point
calculations
were
of 15 geomagnetic results of Vestine's
netic then
field for available,
epoch were
spond to the two of 7. 13 and 5.60 lines
are
Vestine
the
circles earth
geomagnetic
Since
which the
of the
order
of
in latitude best
the the
1 ° in latitude.
The
the
geomagnetic
calculated
ZZ
data
were
in Fig. They
Z. 4 corre-
having radii the dipole
auroral zone of over the North
extended about 4 ° farther as presented by Feldstein agreement of circles is zone
to about in and
one near
and
data
used
between good. that
degree. the
northern
IGY, it seems probable determined auroral zone
with
accord
northern except
may account for minor It is probable, however,
plane.
for
Z5 ° respectively.
Feldstein's
full
configurational
which
plane along
ZZ ° and
degree of latitude. is, within the limits
equatorial
for
equatorial projections
error also is less than one IGY northern auroral zone the
itself.
longitudes
are shown hemisphere).
stations
1945, which of 1957-58.
surface line
less than 30 degrees. of the earth's mag-
epoch
to it amounts
the
earth's dipole
configurational projections
between
dense during experimentally
These
circles are ovals with the longcontaining the 170 ° and 350 °
circles
of observation
quite of the
lations are for epoch with the observations
of them analysis
the calculated curve one. The IGY data that and
lines.
equidistant
out that the experimental with the circle projections
network
zone was in location
plane plane
colatitude
conforms
auroral error
36
in the geomagnetic radii, for which the
difference
projection
the
Two circle projections and Fig. Z. 5 (southern
continent, where the observational
maximal
for
calculations
of the higher approxidipole line in the equaof the
the most recent in the computation.
and illustrated in Fig. 4 show the IGY northern auroral zone The
out
The
of dipole
surface-and
carried
1945, used
Hultqvist pointed accorded well
American south than
number
colatitudes, most et al. harmonic
meridians. hemisphere)
field.
of intersection
The projections of equatorial diameter approximately in the
geomagnetic (northern
magnetic
point of intersection with the pertinent the
corresponding
each The
est
earth's
approximation in the spherical
in the
that the is only calcu-
inconsistencies that this
It is thus evident that the of probable error, in projections
of circles
in
Feldstein's Fig.
auroral
Z. 5 together
with
7. 13 earth radii. from the computed the
better
A question
range
the
of interest zone
merely curves.
computations,
of the
computed is
and
one
whether
the
certainly
the
hemisphere
data
partially account for part of the 6 latitude utable
to
errors
especially Dudziak for
or
et
epoch
zone. zone
by
5ensen
observational to the coast
This means were visible
(1960)
Indeed, since have communicated
(point station. Island-is mentioned zone is
15 on
considerable
zone
in the
Fig.
P. 5),
A small shown
over
plausible
in view
circle projections surprising if the agreement
between
error
of MacQuarie
is
one
only
or
the
close
continent. accord
for the northern two hemispheres the
only
this
Arctic. et al. the
fact
that only is primarily
minor
may a minor attrib-
field,
deviations.
region were far inside the occurring elevation,
they
situated auroral
on
in the auroral a circumstance results.
paper, note
Island,
Bond and Jacka that the latitude south
degrees
zone-the No. Z.
the
more
one Taking
than
near this
of
of Australia that
of the
MacQuarie and the above
into account, it would appear that the auroral with the computed curves, with which it shows
Antarctic
of the
two
for
of in the
Vestine's 1945, when
observational
publication of Feldstein's a report in which region
than
or
computations by harmonic coefficients
discrepant continent
in the
and/or used
geomagnetic
show
auroras at low
IGY
one
data data,
Although
numerical spherical
(1962)
part of their auroral in Fig. g. 5 as curve
considerations fairly consistent
agreement
Cain
in effect that the from these stations
implies
auroral
recent of the
to
the
a real
on
it seems likely over the sea of the
in
nearer
between
Antarctic
sparse.
stations in the of the Antarctic
which
the
and
the
analysis
with basis
and
does.
is
were based field for epoch
very
harmonic
as a comparison a1,(1963) on the 1960
All close
were
5.60
much
Feldstein's
discrepancy
for
in
circle where it is (1945) auroral
of circles
the discrepancy, degrees difference
in the
it is
of the observational of the geomagnetic
greater
shown
of radii
° E,
than
projections
to inaccuracy The errors
are
circles
is
differs quite significantly the course of the latter
rest of the longitude Vestine's and Snyder's
As mentioned earlier, the computations harmonic analysis of the geomagnetic southern
hemisphere
of 320 ° E-90
for the In fact,
with
auroral
attributable the computed
southern
projections
longitude continent the sea.
agrees
southern
the
in the
The experimental curve ones. While it follows
geomagnetic
the Antarctic located over zone
zone
two
types
This between
seems
so much
observed
auroral
hemisphere. showed entirely of curves.
23
Indeed, different
the zone
more and
it would be degrees of
Although, postulating the not
as mentioned above, there are good
circular
processes the only
symmetry
in the
producing aurora possible approach.
geomagnetic
in the If e.g.
reasons
equatorial
earth's atmosphere, the drift around
for plane
it is earth
the
for
certainly of the
primary auroral particles in accordance with the adiabatic invariants the determining process for the configuration of auroral occurrence curves, it is perhaps reasonable to expect that the isoaurores should identical with the lines of constant second adiabatic invariant. Vestine and Sibley (1960) with the projected sible
to judge
Sibley also and Leaton adiabatic
computed such equatorial-plane
between
the
calculated, (1957}, the invariant,J
= fll
Figure two other
zones tical
4 and types
are
ray
particles
the two
dipole curves
based
on
d_/v
in the
, has
km in the hemisphere. 5 include, of more
earth's
that
basis.
the
value
and and
Sprague Quenby's
magnetic
comparison, auroral
cut-off
field,
and
of the internal to observed
heights and
(1960), which and Webber's take
from
-15
km
curves zones: the
are almost iden(1959) curves,
rigidities into
field. data as
and
of Finch the second
Their
hemisphere
of vertical
parts closely
15.7.
northern
be
identical not pos-
Vestine
analysis for which
for purposes of or less theoretical
calculations
and non-dipole conforms as
on
are very nearly it is therefore
the spherical harmonic height of electrons
suggested by Gartlein with the isoclines 76 °,
which
They and
approaches
using mirror
range from 57 km to 420 to 633 km in the southern
showing
two
curves. circles
is
for
cosmic
account
both
Neither of these do the circle
projections. What observed
conclusions
isoaurores
can
and
equatorial lines ?
plane Not too
processes and we
are involved. still expect to find
local
However, conditions
into many,
it can close
be
drawn
projections
the earth's in fact, The the
of
would
expect
the
the precipitation rate occurrence of aurora.
the
circles
similarity
in the
between
earth's
geomagnetic
atmosphere along the geomagnetic since no details of the actual physical geomagnetic circular
be concluded to the earth
mirroring of particles Since the
field symmetry
from the probably
average auroral distribution over the drift of the primary particles around tant for the shape of the isoaurores. one
from
height
data play
and therefore mirror height
Z4
can be strongly distorted for the statistical data. presented a negligible
earth's surface. the earth seems If this process to have
field
that for
The adiabatic not to be imporwere important,
a profound on the varies
above role
influence
on
frequence very much
of with
the
longitude
for one
auroral
J = const
occurrence
would
be
expected.
important
in this
primary auroral scale of auroras
There
This respect
other
be
expected
to show
the
average
southern
netic al.
(1960)
with
the
southern
(d)
and
The pendent (1961)
made
Halley roral
distance
obtained
zone
median
south
geomagn,
of
zone
in
1957
Arctic
(1954-55).
was
than
(1962),
the Asian
is
of mag-
e.g.
Gartlein
et
curves
in Fig.
Z. 6
agreement.
The
the
has
solar
been
cycle.
cycle
found
Sheret observations
1956-59.
The
of quiet
to be
and
made
position
arcs,
de-
Thomas
was
at
of the the
au-
following
1
1956
1957
1958
1959
70.8
71.8
71.9
71.0
fat
auroral
Feldstein
mum
One
years.
Year
The
on
zone
observations
Table
maximum
degree
of the
location
years
that may
plane.
by
a good
of the auroral
in the
from
the time
Kp.
activity
analysis
is not
the isoaurores
evaluated
shows
auroral
solar
than
equatorial
comparison 2.4
and
a curve
drift motion
at a definite
been
increasing
of the
of the
Antarctica,
zone,
in the four
A
in Fig. with
a detailed
Bay,
(1963).
of auroral
the phase
such
of the fact that most
than in the
of the aurora have
increase
pole
on
the
because
parameters
curves
projections
Dependence
in intensity
along
That
expected
symmetry
extent Such
extent
points
need a time very much longer to drift around the earth.
statistical
Feldstein
circle
variations
various
observed.
is also
circular
disturbance.
important
for
is not
electrons in order
are
shell,
frequency
thus
before
who
to
after.
compared
at solar He
closer and
the
activity
found
the
pole
This location
maximum
auroral
geomagnetic pole at the minimum These variations in the location
the
at
the
result of
the
(1957-58)
zone
to be
solar-activity
is
2.5
opposite
auroral and
to zone
at solar
-3 ° closer
that in mini-
to the
of the solar cycle than at maximum. are discussed-also in subsection 6 on
motions. (e)
Auroral The
types
and
type
effects
distribution forms
of
of aurora.
auroral Most
activity of
Z5
the
described basic
data
above are
refers
obtained
to from
all
black
and
makes
white
allsky-camera
it impossible
acteristics
as
It is, are
significant
of fairly
to distinguish
well
as
however,
especially
films
between
differences
between
between quiet
of great
rapidly
and
forms.
whether
different
by positive
which char-
auroral
to know
between
caused
times,
spectroscopic varying
interest
in location
exposure
various
and
theoretical
auroras
long
types
negative
there of aurora,
primary
particles. This is because relations-at least qualitative-between the locations of proton and electron precipitation areas is contained in several theoretical models. For instance, it seems difficult to think of electromagnetic
acceleration
are
together
precipitated In fact,
usually before (After but
midnight rather
been
the
auroral
As
mentioned
auroral
(up to forms.
zone
for
58-76
in section The
red arcs, regions.
° N (at
considered
as
be seen 5 degrees et
al.
the
emitting
observed
aurora
south between expect
alone
there
latitudinal
several
distribution
for instance, No detailed as yet. auroral
to be
the pulsating auroral zone.
His shown
auroras This
often
one
or
zones
different
types
a
of
occurrence
prob-
has its maximum in studies of their geo-
of Scandinavia). are
13)
the "proton the isoaurores
Stoffregen (196Z) has forms in the geomagnetic
approximation,
is
auroral
of the
certainly statistical
p.
forms,
There
located
ordinary zones).
are
(see aurora 1963).
of auroral
1 ° wide in latitude) One would therefore aurora"
particles
produced and Galperin, 196Z).
one,
longitude
a rough
in the figure, south of the
investigated latitude
results,
in Fig.
which
Z. 7.
As
he can
occur most frequently some was also found by Heppner
(1952}. The
subauroral auroral of circles (see
is and
negative lines.
Derblom,
"proton
graphical distribution exist the occurrence of different band
line electron 1963,
from the poles than the the electron precipitation
phenomena.
ability for high the subauroral
hydrogen
Stoffregen
and field
side of the of Ore_holt,
emission
of these;
few degrees farther (which certainly are
if positive
geomagnetic
that
equator reviews
no hydrogen
dark region and the main
the
found
on the (cf. the
north
a distinct aurora" and
it has
is located midnight
processes along
low
latitude
red arcs mid-latitude along the
Roach
and
Roach,
aurora
mentioned
above
is
different
from
the
stable
described on p. 10. The red arcs populate subregions with shape very similar to the projections field lines from the equatorial plane, described above 1963).
between the circle projections of radii Z. 5 and 3 earth radii arcs seem not to exist in the
The
regions
have
their
centers
corresponding to equatorial (i. e. L = Z. 5 and 3 respectively). auroral zones. Z6
somewhere plane
circles These
red
There
certainly
exist
still other
tribution of the occurrence aurora inside the auroral guish
it from
eral,
the
fleeting part,
the
than
those
of weak
ture.
seen
Ray
diffuse
bundles
Inner
arcs
are
auroral
Alfv4'n exist
colatitudes number
if
inner
the
and
to
be
firm
80 ° N
geomagnetic
of the
zone,
that
along
a similar
has
by
more in
ray
struc-
arranged
so as
intensity
and
grounds
that
made
this
to
not.
At
against
at
was
determine
from
time,
clear
it
that
the
(which
the
should
geomagnetic
proposal
this
zones
there
ones,
made,
observations
does
not
zone,
is
not
existence
a
seem
if
it
exists,
unexpected
of
the
inner
zones
discussed
the Soviet
Most
data
maximum
data
is geomagnetic.
in magnetic
most
pronounced is a spiral
in a clockwise
of ionospheric
relevant
activity in the
What
is gen75 The
and shape
latitude-time
direction.
Meek
are
exist-
between
summer.
in a circular
disturbances
to the
(1957)
concentrated
spiral.
hand
Lassen
latitude), activity
around
(i.e. from
activity
show
variable
ordinary
It is
unwinding
geomagnetic
change
In genand
consist,
usually with
Since
the main of view).
Nikolskiy,
the maxima
the other
local
in the
he
auroral seen
course
which zone) from
seemed but
to be
Godhavn.
not
only
of disturbance
Z7
evidence
a type
of the morning.
state
at Godhaven
magnetic
observed
is uncorrelated
the planetary
observing
not find any
time,
sky
in the
of aurora
(1959),
instead
the main
significantly
but with
could
but
6 h.
elevation
morning-type
the
or
zones.
zone
south
of
latitude,
found
found
at great
been
is a morning
system,
occurring
have
favor
auroral
found
of high
degrees.
than point
(1963)
of inner
On
are
theoretical
inside
conclusions.
in
erally
coordinate
zone.
that frequently
these
of aurora. The that distin-
in intensity forms
dis-
reviewed.
Nikolskiy ence
on
exist
pronounced theoretical
briefly
auroral
The
or draperies
10
zones
Observations will
and
bands
5 and
draw
the weak
zone.
of bands
zones
of attempts
is much less from Alfv4'n's
auroral
proposed
auroral
possible
outside
relatively
common,
auroral between
large
latitudinal
zones
(1955)
secondary
are
at the
to appear as part of arcs, (cf. Davis, 196Z b).
(f)
at and
forms
seen
in the
frequency for different types zone has several characteristics
aurora
high-latitude
differences
(about for
an
of zenithal
not
to come
produced The
the
too.
inner
aurora up
from
sporadically
elevation
Lassen with
80 °
did
found local
not
that the
magnetic
Analysing
data
obtained in other parts of Greenland and in the northernmost Canada, Lassen concluded that morning aurora of the described kind is observed in the zenith only along a curve coinciding with the projection of the circle with radius 20 earth radii in the geomagnetic equatorial plane (L
= 20) on the
Witham turbance
et
al
surface.
(1960),
for
characteristics.
parameters, of
earth's
an
could
inner
zone
Davis
(196Z
88°),
Alert
instance, They,
not of
reach
high
any
film
b) analyzed
(era = 86°),
The
from
result
diagram
can
of an
critical
Ray
Diurnal
As ation activity
used.
perhaps
on
remains
to
roral
the
be
activity
The
is
most
and
820
there.
Auroral
used
netic
midnight
from These
local midnight being curves demonstrate
lier local curve
time
marked
with 3914.
from
this in the
of a strong
that if there
81 ° latitude of auroral
is an
over
northern
forms
within
Activity
of
depends of
our and
College
occurs
making
recorded.
of stations
It appears
aurora,
considerably
it phase
"incidence,
(68-69°),
the
=
the number frame of
was
indication
(¢
(era= 7_'b)
counting fifteenth
lack
76 ° and
the
on
the
sunspot
knowledge
the
with
the
type
of
cycle. of
the
diurnal
measures
in the
(64-65°),
1 to 2 hours
the
display much
and
still
variation
and after
activity
previous
of
frequency each of the Farewell local
are
au-
latitude. from
Z8
by
(61-62°).
2.8
Murcray
Fig.
of visual aurora Alaskan stations
midnight,
In Fig. data
"occurrence
subsection.
the
largest for Barrow and smallest a shift of the auroral occurrence
It is drawn
of
auroral Very
diurnal
of auroral
" defined
increasing
vari-
measure
complete.
(after Davis, 1962 a) shows the occurrence a latitude belt of width 1 o centered over Barrow
existence
at Thule Lake
the
prevents
distribution
before
widely
is no
of the number
varies
consistent
and
taken Baker
of forms
There
lie between
Visual
addition,
done
the
various
great.
activity In
films
However,
of a zone
of
season
frequency"
74 ° and
geographical
auroral
disof
about
(¢m = 83°),
Z. 3.
zone.
it must
Variation
does
of
in Fig.
absence
not be
conclusion
total number
that the enhancement
must
magnetic
investigators
scaling was made by distance 80 ° on each
The
auroral
zone,
and
zone
seen
between
of the
auroral
Canada,
Z.
be
definite
the
other
allsky-camera
Resolute
station.
inner
region
statement inner
this
each
many
disturbance.
and Churchill (era= 69°)" The of auroral forms within zenith the
investigated
and
there
Z. 8 in
Geomagdisplacement for Farewell. toward earis also
(1959)
and
a
O
represents
relative
and
1956.
As
ity
located
portant night
allsky
can
be
several
seen
in
hours
difference and
3914 the
later
between
postrnidnight
A
intensity
than
the
this
College
curve
its
This
intensity
Before
during
has
the others.
auroral
hours.
over
figure,
midnight
1955
point
is due
grav-
to an
distribution the
of
im-
in premid-
auroral
forms
stand
out sharply above the low intensity of the background, but after midnight the intensity of the background is enhanced so that individual auroral forms
are
not
easily
and
DeWitt
Davis aurora
was
zone,
for
winter.
has
time)
and
on
Tromholt,
Currie and
and
1959;
and
and
1959,
find
at
of
Fig.
tion
place
from
distance
is
corrected
an for
two
the
higher
At
the
(around
geomagnetic
curves auroral
78 ° only
one
maximum
between
there
were
found
for
time
Fig.
(1964). of
maxima
at
(on
various
29
the
other
the
Fig.
2.
1),
which latitude,
expansion. in
opposite
one at
result latitude
There di-
maximum latitudes
disturbance
au-
observa-
geomagnetic
and
by in
maximum
of
only
of
IGY
resulted
of
3 in
to
for
have
geomagnetic
functions
2.8
secondary
ascaplots
unwinding
same
Fig.
possible
harmonic
dayside)
Similar of
of
the
in
been
distance
The
maxima.
ai.,
found
pronounced,
time
the
10
et
have
not of
found
Also,
occurred two
2.
Feldstein
midnight).
Malville the
function spherical
in
has
(curve
in the
Hale,
Thorson,
Loginov,
curves
geomagnetic
linear
zone,
and
(1963)
zone
Stetson
1959;
midnight.
a less
of
Vegard, 1935;
1937;
1961;
Studies
auroral
terms
Stagg,
occurrence
function
1893;
investigators
Solomatina
the
as
observed
spiral-shaped
by
showing
approximately the
rections.
sented
10
1950;
it
local
by
1933,
Chamberlain
of
fre-
2200
given
Murcray,
but
and
frequency
Fuller,
geomagnetic
1931).
Feldstein Z.
occurrence
to
hours
(Hulbert,
and
the
been
Paulsen,
a,
suggestions
morning
stations
curves
roral
many
early
to
occurrence
also
Solomatina,
close
of southern
(at about
1930;
of these
similar
been
(1960)
and
auroral
period
1886;
1959;
in which
noon.
have
1935
number
of hours
southern
auroral
Elveyetal.,1955;
Feldstein
fairly
to the
midnight
Lee,
Malville,
large
curves
the
some
Feldstein
are
A
have in
The
aurora
Davies,
1961;
maximum
There
of
1953;
1960;
with
maximum
the
1934;
variation 2.9
9.
geomagnetic
1927;
Jacka,
others.
diurnal
around
Sverdrup,
1942;
Feldstein,
1962
close
cent
in a two-months
geomagnetic
variation
Edwards,
bassen,
1960;
the per
Carlheim-GyllenskiSld,
1927;
Brooks,
night
in Fig.
around
diurnal
1882; Chree,
and
is shown
minimum
evaluated
Antarctica,
of day
result
a deep
have
at Byrd,
hour
a maximum
Reports 1912;
(1963)
observed every
Their
quency
distinguished.
has
latitudes
around in
been
pre-
have
been
measures:
e.g.
for
geomagnetic
Nikolskiy dio
aurora
radio
by
wave
On tina
for Forsyth
and
roral
zone
for this
(1961),
who
mapped
eastern
not found
by
Davis
very
on the
previous
gave
similar
surface
subsection).
The
by
extensive
of the
time
(1963
d).
over
curves
case
the
au-
of Khorosheva
similar
of Fig.
2. I0 was
studies
1962,
have
has
distribution
projections
1963)
of some
and
of the
Akasofu
aurora,
of equatorial-plane
geomagnetic
auroral
Soloma1964)
those
configurations
the
and
Akasofu,
regularity
(1960,
to the
along
re-
for
instantenous
auroral
results
instantaneous
closely
earth's
An
of oval-shaped
Akasofu
for
and
at a given
observations
simple
the
by
(196Z)
Feldstein,
proposed
parts the
b) and
made
(196Z)
were
found
and
(1959),
Feldstein
2. i0.
of momentary
and
(196Z
been other
However,
events
Chapman
has
(1957)
al.
al.
also
aurora
in Fig.
among
et
(see
for
et
(1960).
results,
curve
17 cases
2. i0.
auroral
circles
are
Burdo
Hagg
Egeland Piggot
1962)
spirals
hemisphere
to that in Fig.
and and
(1961,
shape
shape
(1955), by
observational
combined
of a similar
Support
which
(1960)
Thomas
that the precipitation
of the two
and
al.
of their
Meek
ionization
Khorosheva
shape
strong
et by
the basis
(1961)
by
sporadic-E
absorption
proposed
the
disturbances
(1957),
field lines
studies
by
(see
Morozumi
(1963)
O
at the
South
Pole
(geomagnetic
peaks
in the diurnal
for a maximum
A
theoretical latitude
siders
the
points
much
of
related as
before
than
(1963)
auroral
the main
tivity occurs
sponding
close
Feldstein processes
and
show,
therefore,
about
That
by
the
in the
that
be
they
or
noon
not
close
two
than
a
magnet-
procalcu-
effect
with
is
8 ° observed).
variations
effects
data
On
been
Detailed
the expected
are
The
day.
have
compared
con-
dayside.
in the
zones
at
one
are
are
of a common evidently of the
needed
oval
in-
reached.
to geomagnetic need
in
the
nonexistence
in the diurnal
in, or
being
(1960).
that Z ° as
observational
the existence can
on
that if the diurnal
sense
More
but
Instead
when
earth
auroral Liemohn
than
one,
zone,
obtained
wind
however,
(less
maximum
found,
is
in the night
concludes
zone
auroral
solar
by
show
occurrence.
around
the
not
a minimum.
oval
instantaneous
(1960)
a conclusion
auroral was
particles
the observed
cause.
an
S) did
at midnight,
(1959)
at all, it is only
for
latitudes
oval
Reid
yet unknown
stantaneous
78 ° , as
at lower
basis and
by Malville less
O'Brien
and
motion
78
there
for
than
are
by Rees
lations
motivation
is compressed
this theoretical posed
curve noon
at noon
drift
which
mirror
variation
at magnetic
higher osphere,
latitude
at geomagnetic
necessarily
to,
30
the
distribution
mean
equatorial
of auroral latitudes
that the plane
take
acof about
correplace
on
the
dayside,
namely
proposed
by
model
proposed That
the
arcs
Axford
the
diurnal
found
by
auroral
predominance
during
the
The
morning.
bright
auroras,
roral
zone,
fore
has
most
3.
and
often
Other
(a)
Time
Z7
day
synodic
ences
days),
for
to the
(b)
aurora
were
known
that the earth
the
in the
phenomena
auroral
the
curve
and
Elvey this
has close
quiet
some
forms
the
appearance near
type
to
have
(1958)
Pulsating
(Heppner,
is
forms
faint
for
forms
which
precedes and
midnight.
of Visual
in of
the
of aurora aurora
authere-
occurs
1954).
Auroral
with
of the
Activity
a period
sun.
of observing
close
aurora,
sun
the
by
a small
Z6
of about
and
the
but
27 days
(Meinel
recurrence
27 days,
the moon
to the solar
effect,
of the no
As
is enforced
around
apparent
synodic one.
When
definite
period
the
analysis
indication which
et al., 1954).
is
influ-
repetition lunar
remains,
tendency
which
considerably
By
of a
evidently
the
second
and
remains.
variation
subauroral two
regions
maxima
at the
frequency
to Mairan
maxima
at highest
the
annual
The
Fig. found
existence
(1733).
in geomagnetic heliographic
curve
equinoxes.
distribution
Observatory.
already
similar
being
variation
is fairly
occurrence at Yerkes
is
for
associated
brilliant
and
Romick
before
activity
rotation
has
hypothesis
incorporated
Alaska, and
generally
by
to repeat
rotations,
In the frequency
College,
hours,
hours
the lunar
Seasonal
are
different
Strong
glow
period
maximum
solar
(1954)
tend
which
one
tendency
possibilities
recurrence
third
evening
well
of auroral
is corrected
is due
the
recurrence
the
responsible
and
for
at
11).
first found
rotation
the
tendency (Z9.5
g.
Variations
Auroras the
(1935)
morning
above
differs
the diurnal
in the
evident
are
disturbances
Fig.
its maximum
is
{1961).
hydrogen
as
A fairly
described
Hines
Fuller (cf.
field
occurrence.
variation
e.g.
zone
geomagnetic
of that model
magnetic and
the
others.
lines
of a kind
for
by
of
and
or
in auroral
spiral
qualitative
been
points
maximum
Two
topology
(1960)
Johnson
that the neutral daytime
if the
It was
by
occurence
proposed
in March
the
Meinel
of spring
disturbances
latitudes
31
of auroral Z.12shows
et
and by are and
monthly al.,
fall maxima Cortie
due
(1912)
to the
September.
If this is true, the angular diameters of the solar plasma beams do usually not exceed about 5° as seen from the sun. This is certainly not so for the very largest solar events, however. The dependence of the seasonal variation on latitude is obscured by the change with latitude of the ratio of the lengths of day and night. If this change is ignored, as it usually is, then the summer minimum becomes progressively deeper with increasing latitude, while the winter minimum becomes progressively shallower, disappears and is replaced by a maximum, which is then the only one in the distribution (cf. e.g. Chree, 1911). Gartlein and Moore (1953) found that the ratio of the mean of the numbers of overhead auroras in North America occurring in June and December to that for auroras in March and September is a steadily increasing function of geomagnetic latitude. Between about 58 and 60° N the level of activity appears to be constant throughout the year. Feldstein and Shevnina (1961) investigated the seasonal variation in auroral occurrence frequency in two hours centered on local midnight-thereby eliminating the influence of the diurnal variation-for
six stations
northern
hemisphere
between and
63
for
and
five
83 ° geomagnetic
stations
between
66 ° and
netic latitude in the southern one. They found the tion as described above at and close to the auroral perceptible roral
seasonal
variation
in auroral
latitude
in the
90 ° geomag-
same seasonal variazones, but no
frequency
on
the
central
au-
caps.
(c)
Sunspot
Fig. tween
cycle
Z. 13,
the number
between
1761
and
the
lar
correlation
occurred,
and
1877 seem
after
delay
of the maximum
solar
activity
but
the delay
4.
Orientation
Hitherto
and
1897 during
sunspot
and
only
various
per
sunspot
auroral 1951.
those
shows
The
The
(1937)
frequency 3 solar
too,
of aurora cycles
a simi-
at Yerkes
auroral sunspot
is good
found
made
maximum year
be-
in Norway
correlation
observations
5 eleven
the
correlation
observed
et al. , (1954)
Egedal
during
the
year,
number.
Meinel
occurrence
activity
cycles found
some
in relation
from
Z
a time
1897
to
to the 1929,
1 year.
of Auroral
parameters
the
(1902),
aurora
maximum.
in Denmark was
with
analyzing
between however, the
Tromholt
to coincide.
when
years
tistical
after of days
maxima
Observatory
variation
Arcs
characteristics describing
the
or
auroral
probability
3Z
"activity," of occurrence
i.e.
of sta-
of aurora,
have
been
this
section
ured
from {a}
described. the
Average
auroral
tend
majority quiet
the
oriented
of the and
often periods
A fairly extensive Hultqvist, 196Z of circles
geomagnetic
tional
the
material,
alignment projection jections served
made for
azimuths
tigated the geomagnetic
be
detail.
In
readily
meas-
and
discussed directions
of such included
values
fact
from
on
circle
the
of all the
ob-
of the nightnot considered.
earth's
Z. 14 pro-
surface
along
the
observa-
Fig.
concerning
2. 14 that,
to the direction that the agreement geomagnetic cases, greater
eastern deviate
that
1958).
of the circle projections where this is under 90 ° .
in
general,
the
of the relevant with the circle latitude than
circles. The ob90 ° in those quadrants
exceeds 90 ° , and Thus, it has been
and western in opposite
circle pro-
coasts directions
less than verified
of Greenland the from 90 ° , as
projections.
Feldstein
(1960)
of arcs circles
and
Evans
at two places differ greatly
auroral zone the prefered
and Halley Bay near direction of alignment
netic latitude projections,
circles, than with
and the
of accurate
average The
reservations
evident
A
data is contained in Fig. are a number of computed
plane
(Hultqvist,
field.
by Fritz (1881). to the geomagnetic number
estimated.
of auquiet
approximately
geomagnetic
investigations
equatorial
lines
than with the is in most
alignment latitude
direction, of the
were the
were
collection b). Also
of the
orientation showed that
only during a certain period different investigations-was
experimentally that on the observed average azimuths
Starkov
can
made a large Scandinavia.
pre-IGY
arcs conforms closely, and
is better arc azimuth
the
into
discussed.
in a preferred
above-mentioned it is
of the quite
where the azimuth 90 ° in quadrants
do
which be
component
bands
in the field
Despite
more
data on the average studies of aurora
investigations (19Z0) referred
arcs
servations were and in different
jections
much early
and the Norwegian school determinations in northern
In the
(after
arcs, will
horizontal
of these early and Krogness
observed
somewhat
of auroral
to be
to the
meridian direction
go
orientation
perpendicular number Vegard
will
recordings,
exist fairly Even the very
arcs
we
orientation
photographic
There arcs.
roral
Now
and where {Dixon
the southern is far more
therefore isoclines.
with
33
Thomas
the
inves-
the isoclines and near the northern
one). They consistent higher
{1959)
found with
approximation
the
that geomagcircle
The are
available
relatively
contained
exiguous.
in Fig.
directions, arrows
as
As
seen
from
directions good
with for
better
all
than
those
Because auroral
and
of the circle
riod
arcs,
(e.g.
point
the
arc
accord
material
of Fig.
Table the
Fig.
with
(1961),
for
is after
(b)
Diurnal
for
stations
dii-ections
if values The
shows
of quiet
8-13
results
for the
values
auroral
from
arcs
northern for
after
Feldstein
variation
in
it was
the
evident
orientation
from
auroral
until the
allsky-camera December
arcs
were
in
the
direction
to end
estimated.
of an
pe-
a com-
of the selected
of Fig.
Z. 14.
at local
midnight
geomagnetic
stations
i-7
(1960),
and
arc
probably
near
and
in
meridian
are
taken
of 1962,
Only
arcs
after
Davis
that for
and
34
not
even
exceed
at
now
from
4° .
of 559 horizon
of
only
(era= 65.3 ° N)
directions
reaching
zones
that the directions little attention was
at Kiruna the
auroral
of Bravais
distant ones, covering in the analysis. The does
the
observations
ninteen-thirties,
recordings 1958
izon or, in the case of the most of view of about 100 ° were used ured
arcs
(1945).
paid to this phenomenon few studies exist.
From
of such
of
of them in or near 2 and Fig. 2. 16. A concordance
Bossekopin northern Norway as early as 1838-40 the arcs and bands show a diurnal variation, very
the period
certainly
a short
is better
azimuths are
fairly
is
of the
for
that the
the unselected
observed
Harang
Although
compared.
(measured
The
the
expected
projections
azimuths
hemisphere
those
Troms_
circle
is
in the orientation
at twelve stations, most are presented in Table
Z. 16 than
the east).
circles
agreement
variation
between
2. 14 clearly
the
Z contains
northern
towards
are
observed
circles.
is to be
of the night
of the
results.
between
the
during
in direction of the
plane
and
of a diurnal
increased
with
directions
9),
of
Two
of observations
agreement
latitude
existence
results
equator
(No.
is
elevation.
differences
the
data
of observations
the uncertainty
15,
hemisphere
subsequent
results
of highest
The
projected Byrd
parison for local midnight the northern auroral zone, comparison
Z.
southern
and
the
1958.
Fig.
projections
1 hr)
represent
and
geomagnetic
of the
the
auroral
except
the
of IOY
demonstrate
of
places for
indicate
station
will
be
arrows
1957
years
the
collection
single
two
for
A
to the
for the
results
The
years
of the two
arrows
2. 15.
sighted
for any
each
observational
in
quiet to hor-
an azimuth error in the
angle meas-
Table
Station
No.
Geomagn. Coord. °N
Z
Observed
Approx. measure of deviation
azimuth °E
(degr.)
Azimuth of circle projection ("theor. azimuth")
Diff. obs. azimuth and "theor. azimuth"
i
1
Baker
Lake
73.8
314.8
Diff. max
94
_60
-min
93
O
Z
Churchill
68.8
322.5
99
Diff. max -rain o 60
95
4
3
Barrow
68.6
Z41.Z
92
Diff. max -min o _60
84
8
4
Fort
66.6
256.8
9O
Diff. max -rain o _80
87
3
5
College
64.6
256.5
86
Diff.
max-rain _60 °
87
-i
6
Farewell
61.4
253.2
83
Diff.
maxmin _60 °
86
-3
7
Choteau
55.5
306.0
88
Diff.
max-min _70 °
95
-7
8
Schmidt
62.6
226.6
8O
Diff.
max-rain _30 °
8O
0
9
Dixon
63
162
98
Stand.
deviat.
98
0
°
I00
3
±15 °
ll3
-2
Yukon
I_.Arcs w,th ray-struclt_r¢
.-_ orape___m
---
,C"2._.
L
,o t 6O
I, 40
I
I 20
i
I
I 20
I
I zg)
i
I 60
J
i 80
I
J tO0
i
Number
Fig.
Z. 24-
(After
Vegard limits
and Krogness, 1920) Distribution for different auroral forms.
of lower
t20
.8 m
A
m
O
m_ °r-¢
00 m
f
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J
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20'
Draperies
th ray.-struc
10
-----"
Fig.
Light
Z.Z6-(After
intensity
Harang,
tribution of light intensity ferent auroral forms.
1951) along
Disdif-
14 -
I0
-
_
INCIDENCE .
.j
MAX
KCO
>5
-
m
'_'_,_.,. MAX. I r_-_
I i
0-
I
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B
I-_ _ 60 z,.,u UU e'O
I
I
I
PERCENT
n
_
OCCURRENCE 19-05
HRS
--STRON_
O
I
I
I
I
Cf
,.-I,
"_.
WEAK
j
90 I o
I
_
_
KCO ':5 I
I
I
I
_
K
i
_
I
INCIDENCE
STRONG
Ilg
...
9_
_'-_TRONG
70
68
Fig.
66 GEOMAGNETIC
2.28-(After
measures
of
Davis,
auroral
itude for weak
and
inAlaskainthe of
total
64 LATITUDE
62
1962b)
activity
strong
for
Several
versus
displays
season1957-58.
incidence
25
60 °
lat-
observed (A) Curves
displays
during
which the maximum did not exceed 5
K-index for College (dashed line) and for 25
displays
it exceeded
(B)
for which
Average
percentage
of overhead
auroras
19,05 h ) during (C)
Total
strong curves moving strong
and
(C)
forms and
30
and
observed weak
weak
displays.
interval displays.
during
displays
Total
occurrence
time
of forms
24 weak
B.
(local
24 strong
incidence
5 (solidline).
hourly
used
south
and
throughout
the
24
to draw north 31
0
Q; (D
_
.,-4
o o
o_ 0
0
o
o
°r,,I _-_
_ _j
_
0
0
_
om
_o_ "a_-
.a
_o_
_o
_'_ _
-,_
o,___
o _,'_
u
0
3. In
Correlation
this
and
solar
i.
Solar
section and
the
with page and
number
planetary
of
the
3Z), solar
Since
magnetic reached
recurrence
than
for
magnetic
aurora Uppsala,
of
aurora
be
in
occurrence mentioned
storms seems
in
the correlation have been made.
solar
(cf. below),
fre-
events
and
most
between A
geomag-
in Chapter aurora and
of
of the
are
also
valid
to be
less
pronounced
relevant
for
aurora. for
aurora
1961).
discovered
in
of
and the
has
been
in
subauroral
known in
by
only may
times
Celsius
long
day
the
been to
Hiorter
when
in
in
by
Barrels
investigators
invariably
the
seen
occurrence
made
aurora
almost
latitudes
be
when and
between
zone
aurora
the
1940).
has
for
the
auroral
latitudes
little
1741
Barrels,
activity
storm
aurora
at
correlation
magnetic
It
very
in
Chapman
a magnetic of
occur
the
storm the
leads
to
following is
a
auroral
night.
strong
one
zone
(see
Z).
visual
the
central
aurora
planetary latitudes
is
K
ireldstein Murchison a weak south
polar
75
and
80 °
the is
(196Zb)
found
Bay
{geomagnetic
magnetic
that
taken
between
{K
= Z-3).
account
57
of
observed
75 °N) the
as
as
with
occurrence
in
the
frequently
When
auroras occurrence
the
geomagnetic and
a transitional
most auroral
80 ° ) the
well
between
auroral and
are
latitude
above
local
region
complicated auroras
into
the
In the
relationship more
latitude
with
1963).
disturbance also
{geomagnetic
correlated
{Davis,
activity
were
caps
negatively
indices
geomagnetic
the
the
been
of to
not
disturbances
planetary
of
cases
Over
is
have
{Chamberlain,
was
{1958).
occurrence
Section
is good
investigation
true
of
between
magnetic
{cf.
the
start
is
which
relations
magnetic
observed
and
which
reviewed.
variation
investigations seem
tendency
Sweden
Chapman
This
briefly
aurora
Disturbances
A detailed
the
for
worldwide can
in
the
cycle,
disturbances
Geomagnetic
the
be
visual
in the literature and are reviewed correlation between occurrence
activity
Z7-day
That
solar
of
exist the
The
and
Phenomena between
will
of
detailed disturbances
studies
conclusions
that
Geophysical
phenomena
investigations
aurora
netic disturbances of this book.
Z.
and
statisticalrelations
geophysical
Z {see aurora
large
observed
for
of
Section visual
Solar
Disturbances
Except quency
with
nature.
zenith
at when
there
appearing frequency
to
-
increased found
with
positive
disturbance
K-index
is not
visual
only
as
of the associated
been
studied
by
(1953,
ultaneous
(1954b)
be
in the following
auroral
activity
represented
disturbances
The
by
each
bay
patterns
horizontal
distinct
change
from
College slowly
observed the
pattern) the
A nosity
period
have
Zabor-
(1959)
and
has
close and
quiet
and
Close
following
during
pattern).
geomagnetic
between
also
rapid
micropulsations
Campbell(1960 (see
A
bay
north
as
luminosity
bay up
sets
(first
of Heppner
during
the
of cases horizontal
arc
or
than
is generally
pattern
the
homogeneous
The
breaks
majority
in which
far
a
time
a negative
and
place
being
frequent
glow).
when
from undergoes
appear-
there
is
magnetic
is frequently
this period.
correlation
(1963)
and
takes
bay
disturbance
at this
magnetic
In the
the negative
that coinactivity.
the
aurora
In the first
component
is positive.
when
southward
aurora.
and
is more
to the moment
(second
individually
of auroral
the
sim-
all, nights
that magnetic
is generally
(arcs
moves
apply
it disappears
positive
and
field changes
aurora
forms A
active,
pulsating
the
(geomagn.
perhaps
disturbances
first pattern
night
and
happens
second
The
at College
which
geomagnetic
in the
equatorwards.
component
again
Nebel(1959), Berger
and
to what
of the
of the horizontal
disturbance formed
develop-
1955),
of recognizing
In the first pattern
of the
becomes
of diffuse
a short
development the
disturbance
patterns,
sequence
and
disappears
recovery
ance
of
relations
et al.
of,
is a distinct
in respect
in this period. aurora or
of two
far northward.
part
magnetic
majority
bay
negative.
In the early
The
a large
of individual
there
in form
recedes very the second.
advances
up
component
to being
in,
the and
These
observations
is a consequence
differ
positive
seen
made
his
way.
on
means
This
are
with
two
in the
between
latitudes,
Bless
Pole).
occurrence
(1954a,b,
(1958),
(1963)
magnetic
South
general
exists zone
Heppner
Fan
summarizes
in combination.
cident
the
disturbance.
1954b),
(1957),
and
(at the
between
in auroral
Morozumi
occurrence
latitude
relationship
seen
of it.
(1963d).
lat. 64.5°N)
or
Meek
values
auroral
geomagnetic
Fediakina
Heppner
may
between
detailed
ment
Akasofu
high
a correlation
aurora,
shchikovand
to
at 78 ° geomagnetic
but a fairly
of the
up
correlation
even
There aurora,
the
a,b,c), Chapter
variations has Campbell
).
58
in the auroral
been
found
and
Rees
by
lumi-
Campbell
(1961)
and
and
3. Earth Currents The
occurrence
wires
was
height
measurements
used
a warning
by
aurora
earth of
StSrmer
of
Wescott,
accumulation
auroras,
with occur
to
the
the
two
corresponding
phenomena
an
for
influx
telegraph
paralactic
As
years
the
is,
cases.
at
earth's
good
reported
of negative
precision and the
The
however, has
as
electric
with adequate electrical field
(1961) the
long
many
night.
in individual
charges
to
next
not known induced
the
in for
success
the
Freier
negative
voltages program
good in
aurora
1959). of
induced
extensive
is generally details of
currents
and
of
his
aurora
would
occurrence
Hessler
day
in
of the ground to relate the
resulting lation
the
on
that
conductivity it is difficult
the
during
corre-
(cf.
e.g.
evidence
surface
for
during
charges
into
the
upper
atmosphere.
4.
Radio
Aurora
Reflections
of
frequencies radio
of aurora
(1938,
were
America, and
The zone
see
for
an
The
seasonal
The
long
Z years
Radio aurora. very
narrow the
same
the
height height
aurora
and
the
1930's particularly
-
Stoffregen
by
is
amateur during
a number
of
Germany,
of radio
critical
ionization
and by
(1962),
activity,
power
range
well
has
with as
far
as as
zone
Russia,
aurora
the
researchers
with
Hultqvist
and
observed
in the
as
same
auroral
New detailed
Egeland
has
value
59
at the
visual
echoes
can
3. i).
equinoxes. about
aurora.
regions
as be
optical recorded
zones.
to take
between
border
auroral (Fig.
its maximum
with
general type
found
maximum
maxima
the auroral
been
mean
has
is the case
from
the lower
a night
variation
in the
radars
process
interval
aurora
as
frequency
in latitudes
reflection
in
Sweden,
of radio
is observed
high
even
Harang
auroral
war
a review
in the auroral
solar
aurora
by
via
studied
Egeland
maximum
occurrence
With
often
The
variation
variation
after
For
the with
(1964).
afternoon
term
been
Norway,
instance
Leadabrand
1938
earlier
has
Britain, Antarctic.
diurnal
has
in
world
above
associated
propagation
second
aurora
the
references, and
the
well
ionization
discovered
radio
Z@aland
frequencies
investigated wave
After
in North
(1964)
first
however,
years
of from
radio
operators. ten
waves
ionosphere
That
was,
radio last
-
1940).
possible
radio
the
90
of visual
place and
in a fairly ll0
kin,
aurora,
by
i.e.
in
a large
number
of
investigators.
quite
wellwith
Fig.
3.2
radio
aurora.
Also
those
shows
of
visible
can
The
be
seen,
does
not give
The are
echoes
mentioned
found
is
sensitive: to
any
to
the
the
magnetic
stood
if
the
field
strongly reflection
a critical
ities.
Recently
sound
waves
echoes the
same
et
small
al.
is
,
5.
1964)
it
zero
the
But
the
1963).
fine of
overhead
auroral
echoes
is
aspect
a direction
perpendicular
This
can
be
scattering
lines
of
the
as
small
well
as
if
irregular-
irregularities of
reflecting
under-
from
force,
structure
may the
centers
by
ion
received are
be
of
active
be
at
fairly
well
Anderson,
seems
that
well to
be
(see fairly
to
the
most -
refractive part
of
the
clear.
large
of
scale and
VHF
See
1962;
Anderson
auroral
luminosity 3.4,
exceptionai
after in
x-rays
the
is and and
activity. of
in
x-ray
quite 1960).
flux and
zone
the
general
Enemark,
Anderson auroral
has
magnetic
precipitation
bremsstrahlung,
60
the
reflection
from
occurrence
aurora
Fig.
from
Altitudes of
generate
far
Mc/s
details.
correlated
1960,
happen
extremely
Balloon
between
which
is
that
2850
scattering
lowermost is
more
probability
correlation
(cf.
This
the
the
to
critical
large
produced for
weak
distribution so
in
are
up
whereas
importance
at
that
density density
papers
frequencies
probable
frequencies,
electron
zone
however, other
most
for
electron
X-rays
to
there
each
which
weak
the
observed
an
electrons,
does,
the
review
detailed
energetic
been
higher
may
auroral
found the
poor
of
that
The
irregularities
Bremsstrahlung
been
or geomagsouthern
magnetic-field-aligned
suggested
seems
in at
mentioned
In
elevation
aurora
point.
one
along
number
has
from
How
above
not perfect
at low
mechanism
reflection
1963).
aurora
reflection
band.
in from
larger
been
a large
process
index
regions reflection
is
from
irregularities
i.e.
the
elongated
has
that
radio
important
It
it
but
p.44).
and
time.
As (Groth
at
(Buneman,
shows
the
the
mechanism
it
Z (see
of visual
only
strong
predominantly
lines
irregularities is
that
occur
reflection
Section
around geographic and south in the
extremely
of
fact
reflections
good
correlate
at all.
limitations
due
in
is a significant
somewhere hemisphere, Even
aurora
recording
is, however,
3.3).
radio
described
there
correlation
(cf. Fig.
of
of simultaneous
angles in a sector centered netic north, in the northern hemisphere
motions
aurora,
an example As
correlation.
the
foliow
DeWitt, latitudes.
In subauroral latitudes strong x-ray events occur almost only during strong magnetic storms, and the correlation between the occurrence of visual aurora and bremsstrahlung at balloon heights is quite good (see the review by Winckler, 1962, for instance). The balloon responsible tute the aurora
6.
the
The detail
in
Auroral
spectrum
Rates
the magnitude short
This
the
SIDs type
is no
has
phase
and
Even
is
not
consti-
the visible subauroral
in
discussed
in
•
•
no
if
there, and
visible
with
any
some
Ansari when
auroral
shows
with
type,
reported form
regard
aurora
(cf. Chapter observed
that Ansari than
occurring
one
type
of
spectrum in the pre-
the visual
aurora
(see
to the luminous
( 4.
satellite
for
daily value
electrons
Brown,
the variable
combinations electrons
x-rays
primary
producing
explains
the the
energy
the
the
summer
should
days to
in
activity
month, For
when
the
db during
each
the
This
1964,
fluxes
in
the quiet is identical
to the 1963,
in
1 db
bremsstrahlung
compared
from
magnetic
(1963).
profile
flux
and0.09 of
days
equinoxes.
For which
db, absorption
Basler
about
electron
ranges
quiet
density
computed
4 as spectrum
db
limit
2 sec
given
the
by
the
spectrum
is
the
equivalent
found by is curve
68
as in
McDiarmid No. 1.
and
absorp-
spectrum
coming
in
1.9
db
and
(1964a).
to
three
well the
equilibrium 3.8
db
the
is
Hultqvist
spectra are
-1
Z
mentioned
energy
kev)
due
Curves
is 0.Z7
absorption
After
for
the curve
represent
differential
profiles
Mc/s
elec-
under
at night.
day
produced
e-_/s
of the
in the
daytime db.
The
Z7.6
produced key)-1
absorption
= 5.109
to 0.89
(cm
electrons.
No.
N(E)
3, finally,
by
density
at
of the
absorption
Total is
A,
fluxes limit
et al. (1959).
allsky-camera
total absorption
and
electrons
absorption,
ster
from
to the bremsstrahlung
produced
electron
Z gives
The
day
Total
one
precipitated
spectrum
kev) -I.
lines.
nighttime
sec
curves
to the geomagnetic
Leadabrand
altitude.
distribution
in the
-E/41
3.6-Equilibrium of
to the various
obtained
at balloon
due
0.061
tion distribution
along
with
of range and The points repre-
regard
After
luminosity
energy
spectrum.
in the night N(E)
with
point.
height
ster
amounts the
attached
angle
flux
differential (cm
electron
compared at College,
a function Z6, 1957.
numbers
reflection
x-ray
aurora obtained
(1963).
1 show
trons
Fig.
of
of auroral
DeWitt
aurora
(1954).
observations.
at the
for radio (geomagnetic
(1962a).
radar
Bowles
sent
pictures
Fig.
Egeland
3.3-Mass plot of 398/Mc/s echoes as azimuth, College, Alaska, March
field lines Fig.
After
photographs 106 Mc/s
Alaska.
Fig.
of the occurrence frequency observed at Kiruna, Sweden
65.3°).
3.2-Allsky-camera simultaneous
Captions
energy as
the
spectra total
figure.
Curve
electron • 104
spectrum et After
e -E/s° for
density electrons the
al. (1963) Hultqvist
average a lower (1964b).
(cm
2
Fig.
3.7-Diurnal noise PCA's
variation
of the for
the
occurred
are
excluded.
for the following months: 1959, March 1960, October tember 1961, and October alone Fig.
3.8-A
average
absorption
and
curve
simultaneous
3 for
intensity
equinoxes
at
of 27.6
Kiruna.
Curve
1 represents
April 1959, September 1960, March 1961, 1961. Curve 2 is for
September
observation
1959. of VLF
auroral luminosity and precipitated on March 3, 1963,0720-0725 UT. (1963).
69
Mc/s
Months
After
cosmic in which
the
average
1959, October April 1961, SepSeptember 1961 Hultqvist
electromagnetic electrons on After Gurnett
(1963a). emission,
board Injun and O'Brien
3
Fig. 3.2-Allsky-camera photographs of visible a u r o r a c o m p a r e d with simultaneous 106 M c / s r a d a r e c h o e s obtained a t College, Alaska. After Bowles (1954).
i'
0
0
0
0
0
0
0
0
0 0
104 . i .
I
-
MARCH
'
I
I
5, 1962 rr
_)
I
iO_--
RAYS
>25
keY
U
_
3o
8 z 2.0 -_
_> 1ol I "" .... 1200
Fig.
_,,
1230
3.4-Comparison
camera and
t
pictures
DeWitt
(1963).
1300 1317 UNIVERSAL TIME
of with
1.o""
auroral
x-ray
flux
luminosity at balloon
1400
obtained altitude.
1430
from After
allskyAnderson
140
140.
NIGHT
DAY 130
130
120
120
I10
I10
E I00
I00
90
90
80
80
70
70
60
60
50
50
W
b-b--
40
40 0
2
4
6
8
I0
12
0
2
4
6
8
I0
12
Fig. 3.5-Curves 1 show the height distribution of the absorption produced by the differential energy spectrum N(E) = 5.109 e-E/s electrons (cm 2 sec ster key) -I The total absorption under to 1.04 db in the day and to 0.89 db at night. Curves tion due to the bremsstrahlung
of the mentioned
the curve amounts 2 give the absorpelectron
spectrum.
Total absorption in the day is 0.27 db and in the night 0.061 db. Curves 3, finally,represent the absorption distribution produced by the differential energy coming
spectrum
N(E)
= 7.104
in along the field lines. Total
the nighttime
one is 0.52 db.
After
e-E/4z electrons daytime
Hultqvist
(cm 2 sec kev) -I
absorption (1964a).
is 1.9 db and
140 I 30
I
I
I
m
120 I10 I00 Km
90
/
/
/ 80 70 60 50 I
40 I02
I
tO3
I
iO4 electrons/cm
tOs
I01
3
Fig. 3.6-Equilibrium electron density profiles due to three energy spectra of precipitated electrons. The spectra as well as the total absorption,
A,
at 27.6 Mc/s
are given in the figure.
Curve
No. 2 gives
an upper duced by
limit for the equilibrium electron density distribution prothe spectrum 3.8 • l04 e -E/3° electrons (cm 2 sec ster kev) -I
which is the equivalent spectrum for the average fluxes when Kp > 4 as found by McDiarmid et ai.(1963) a lower limit for this spectrum is curve
No.
1. After Hultqvist
(1964b).
Absorption 2 db
in the first
•
i
minute of each hour
|
!
i
i
!
A
#
/
,i
a.
/ # i
/
i
/ /I
!_ A
/
l
_,\_) _
_.._
;v l
•
3
6
9
Peak absorption
12
for each
.j
15
18
21
hour
I^"
2
b,
._t j
db
/,
\
,
fj/
•
,
24 MET
\
',
"
,'/
_,
-_.
v _\
Q A'
#
d 0
i
i
u
u
!
i
I
3
6
9
12
15
18
21
2,4 MET
Fig. 3.7-Diurnalvariation of the average intensity of Z7.6 Mc/s cosmic noise absorption Months
for in
the
which
cluded.
Curve
for
following
the
September 1960,
equinoxes PCA's
I represents
October
196 i, September Z
is
curve
3
for
for
1959,
March
1959,
1961,
1961 1959.
ex-
March
196 I, and October September
September
qvist (I 963a).
are
average
April
October 1960,
Kiruna.
the
months:
1959,
Curve
at
occurred
alone After
April
196 I. and Hult-
L (EARTH I
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--
;_
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'
8A H_ -
>n,,
_.p
,
_40
than
published
degrees
degrees.
results
the percentage
from has
70
presented
The
auroras
of precipitated
of interest
latitudes.
of
on the been
(1963).
a few
range
kev
and
auroral
data
above larger
of the invariant
seen
40
60
electrons
with
range
be
>
Similar
their
al.
at the most
subauroral
the
ten.
for
et
the
can E
A between
lower of
for
data
recently
3 observations
in the latitude
degrees.
for
have
Injun
(i/L) I/2 and
latitude
that
of magnitude
statistical
electrons
1964)
orders
shown
4.1).
precipitated
diagram
have
1964).
close as
to the
observed 1964).
4.
Electron precipitation occurs simultaneously in magnetically conjugate areas at least sometimes, according to balloon observations of x-rays (Brown et al., 1963). This is in accordance with observations of aurora (cf. e.g. DeWitt, 1962). A I00 fold change in the flux over two km has often been observed by Injun 3, which is in agreement with results of rocket measurements in aurora by Davis et al. (1960). They found the electron flux being concentrated in the visible auroral forms, whereas protons were found over a much larger volume than that occupied by the aurora. The with
E
statistical >40
latitude
kev
has
profile
been
found
maximum at a few degrees rence of visual aurora as the
visual
emission
precipitation
of
electrons the
of
higher
with
has
the
E < 40
lower
O'Brien
and
never
are
Taylor,
observed
to
of
was
found
It can
be
up
and
near
than
in the 4.Z
about
The
the
radii).
latitudinal over This
L
have
latitudes 40
kev,
to
higher
of
the
its
than
the
indicating latitudes
aurora
than
coincides
(OtBrien,
4.4
also
give and
auroral
a good
At
extent
% l earth
is illustrated
or
in Fig.
very 4.5.
74
electrons
(cm
emission
in the rate
emission L
zone
1964;
ster) -I
auroral
zone
the enormous
are
values
figure.
This
can
be
very
(over
L
3
2 sec
at all latitudes,
extensive
Injun was
is, however,
about
= 6 there in the there.
by
= 6 there
emission zone.
of the precipitation
radius)
at L
impression
photon
zone.
auroral
that
80
photon
6.106 electrons (cm 2 sec ster) "I shown 105 times the minimum value observed
(e.g.,
to
of occurSometimes
precipitation
in Fig.
continuous
of precipitation
especially
higher than
limit
all the time seen
flux lower
corresponding
variability
to
appreciable
electrons
(1964)
the frequency satellite.
greater latitude
dumped
1964).
any
4.Z
than same
extend
is evident from Fig. 4.4. The minimum below visual threshold even in the auroral
Figs.
of Taylor
precipitated
lower
limit
and
energy
being The
latitude
1964).
The
key
intensity
latitude on the
found
with
ones.
Precipitation (O'Brien,
been
the
O'Brien
lower observed
electrons
energy
of
by
but
of about is some
restricted > Z0
earth
(b) Time Characteristics
of Precipitation
It is not possible to differ between time and space variations in satellite measurements. Balloon observations show, however, that time variations as rapid as of periods of a tenth of a second can occur in the electron flux (Winckler et al., 1962). No systematic over
periods
the Injuns
as
as
flux
tc_ be
earth
sary
for
(c)
O'Brien
(1962a, angle
flux
made
also
tendency
of precipitation
electrons
..;_ of the
however,
variation
neces-
curves.
earth's
important.
by
has
becomes
has
electrons
of E
in the
been
> 40
higher
by
key
of strong
et al.
(1962)
in which
the
than
the
of intense
in regions
found
mentioned
the
found
regions
Krasovskii been
over
been
is
equal
the
at an direc-
correspond-
observations
were
atmosphere.
seems
to indicate
along This,
of electrons of the
that
distribution
have
The
the precipitation
is increased
rule
isotropy
electrons
atmosphere.
the role
is not
polarof the
variability
electrons
also
angle
cases
to isotropy
tions
that
oriented
seems,
diurnal
daytime
kev--as
._,o_
where
that for
observed
No
it is directed
from
which a general
electrons.
to the
away
suggest
than
distribution
of data
aurora,
pitch
been
i0 kev.
close
the
the
approaches
isotropic
trapped
electrons--if
of an
from
for trapped
0.08--Z4
enormous
of precipitated
namely
of precipitated
fairly
The the
has
for
the
amount
(1964) case
nighttime
_h_,_ _,,__
significant
electrons,
b, 1964)
of about
ing value
flux
i illustrates
An
precipitation
the
range
lifetime
With
that over
distribution
precipitation.
a higher
th_ _ay_
1964).
O'Brien
with
the energy
precipitation
Distribution
of trapped
Figure
found
a large
directional
aurora.
tional
on
by
energy
5 days
also
statistically
i shows
to the flux
the
They
et al.,
Angle
the
energy
in the
phenomenon
Figure intense
pitch
observed
deducting
Pitch
be found
of electron
in contrast
of electrons
harder
(Johnson
precipitation
could
et al. (1964)
satellite.
elect_nnq
intensity
as a day
of protons--during
orbiting
in the
3 measurements,
Sharp
precipitation well
long
! and
electrons.
variation
that the
acceleration
the field lines--takes as well
from
ionosphere O'Brien
above
mentioned
i000
km
in the production (1964)
75
as the
found
place
of
far
observa-
in auroras, of the
a flux upwards
energetic along
the field lines, which was some 10%of the precipitated electron flux. He interpreted these observations as backscattering of electrons from the atmosphere.
(d) Kp - Dependence of Precipitation The Kp dependence of the precipitation of electrons of energy above 40 key is illustrated in Fig. 4.3. The average intensity was ten times higher near the auroral zone when Kpwas above 4 than when it was below 4 • The data material for the higher Kp range in Fig. 4.3 does not
contain
may
be
data
O'Brien 40
kev
A
close
for
any
(1964)
increased
strong
found on
magnetic
the
0.08-Z4
together
with
observed
storm,
range
Injun
3
in
the dependence
1963).
close
to the
by
so
still higher
of precipitated a factor
precipitation
energy
on
in the
(Freeman, larger
average
between
kev
obtained
that the flux
the
correlation
results,
as
from
values
expected.
by a
intensity
Sharp
low
are
of the
omnidirectional
plane
far
As
seen,
can
be
(at one
from
the
end
preferentially
parallel
was
in
Fig.
above
by
Kp dependence
of Kp.
observed
O'Brien's
shown
earth
above
step
also
flux
the
4.6
40
key
Explorer
is very
of the field line) than
torial plane (at the middle of the field line). increases are due to a common acceleration it acts
every
et al. (1964).
orbit,
equatorial
earth
electrons
of 5 for
IZ
much
in the
equa-
If one assumes that both mechanism it follows that
to the geomagnetic
field lines
(O'Brien,
1964).
The Fig.
change
4.6b,
of E _> 2 Mev
The
of omnidirectional
is opposite (Arnoldy
dependence
activity
has
used
data for
trapped
of the terms
was
of energy For
studied
has
above
this boundary,
40
kev
Maehlum but
(1963)
boundary could
measured
their
found of the
be
observed
in L,
they
76
shown
in
electrons
of precipitation O'Brien
O'Brien
close
on
(1963).
(1964)
to the
results
of precipitated
Kp,
for
et al., 196Z).
and
since
with
observed
boundary
electrons,
O'Brien sharp
40 kev
been
Hoffman
its maximum
extension
and a very
by
electrons,
of trapped
of possible Maehlum
there
been
above
mostly
et al., 1960;
precipitation
region
flux
has
of the poleward
netic
that the
to what
has
be
They shown
poleward
may
mag-
boundary
interpreted
in
electrons.
that during region
at about used
magnetic
where
the
storms
trapped
I000 symbol
km
electrons altitude.
L n.
It can
be
seen 4.7. value
as
a function of the Kp index during one geomagnetic Kp reached its maximum value of 9, L had of 4. Maehlum and O'Brien (1963) also found that
edge during
of
storm in Fig. its minimum the poleward
When
strong radio the storm.
wave
absorption
followed
the
L n quite
closely
The effect of Kp on L n is similar to the equatorward movement of the region of visual aurora during strong magnetic storms, which has been studied in the last few years in detail for some storms by Akasofu (1962, 1963a,b) Akasofu and Chapman (1962) and Davis and Kimball (1962).
(e)
The
Spectrum
of Precipitated
Up to now of the precipitated proposed spectra
only
rough electrons have been
Electrons
measurements of have been reported. obtained from two
the
energy In most instruments
spectrum cases the with differ-
ent energy characteristics. They thus are to be considered as rough equivalent spectra for measurements made in a defined way. In addition, it has been found that the equivalent spectrum is highly variable both in space and time (cf. O'Brien et al., 1962). Nonetheless the available spectral
data
are
the field, and they conclusions about Section 3). Most two
spectra
categories
hand,
the
steep
interest
even make ionospheric
that
have
if they e-folding
written in the key (McIlwain, very
of great
are
spectrum,
been b,
reported
even
has 1963; steeper
Krassovskii
cipitated 14 key.
electrons
The Geiger about much
majority
et al.
(196Z)
with
a most
of the
existing
has common
of knowledge
in
interesting electrons
be
(see
divided
form.
On
of precipitated
in one
electrons,
been found often to be in the range2-8 Sharp et al. 1964 a,b,c.) This is ones
have
been
observed.
Mc-
in a strong aurora as with an energy of about
observed
steep
equivalent
measurements
tubes, for which the minimum detectable 40 key. These measurements have mostly higher than those mentioned above, namely
77
can
exponential
spectrum
Ilwain interpreted his rocket measurements indicating a monoenergetic flux of electrons 6 key.
stage
hitherto
in an
in the
exp (-E/b), Stilwell, but
present
it possible to draw some effects of the precipitated
expressed
value,
form _ 1960;
at the
spectra energy
have
been
for
pre-
value
of
made
with
electron energy given e-folding between Z0 and
is values 45 kev.
a
(Davis et al. 1960; McDiarmid et al. 1960; et al. 1963; McDiarmid et al. 1963; O'Brien et al. (1963) the values 42
found
from
within
measurements
this range
were
O'Brien et al. 1962; and Taylor, 1964).
during grouped
only
in two
some
Z0
classes,
Mann Mann
orbits
Z5
that
+ 5 key
and
+ 3 key. The
balloon
general,
give
energies
in the
Enemark,
measurements
spectra range
1960),
observations
better
with
seems
crease
fast below
type
the
dayside
with
low
lower
Of
that the
1 kev,
which
reported
riometer
down
special
to e-folding
are
found
and to fit the
of precipitated
electrons
et al. 1963,
1964c;
Evans
(O'Brien
spectrum, means
and
Taylor,
in general,
that
1964).
does
it is not of the
not
in-
power
energies.
et al. (1964)
located
in
spectra.
(Sharp
in aurora
on the nightside
multifrequency
Lerfald
also,
e.g., Anderson
often
measurements
height
et al. (1964c) than
(see
exponential
reported
altitude
corresponding
spectra
than
been
probable
at these
Sharp
law
km
showed that there is generally not very much energy This is also evident from observations of the lumi-
It therefore very
power
have
distribution
law
mentioned
key
first direct
energy
et al. 1964). They flux below 1 key. nosity
flat type,
20-45
although
the
1 key
at 30-35
of a fairly
somewhat
Recently below
of x-rays
interest
to which
atmosphere
are
earth.
measurements
according in the
a significantly of the
the
harder This
spectrum
of auroral the
in the
statistical
data
by
ionization
than
on
agrees
absorption
absorbing day
on
observation
in the
electron
is
night.
precipitation,
published recently. As mentioned earlier the precipitation is most intense near the auroral zone. O'Brien (1964) found an average flux of 4.10 s electrons/cm
2 sec
in the precipitation
tude
of 65 °.
Injun
1 had
above
about
1 key
(O'Brien,
that the
a CdS
detector, 196Zb).
flux of 4.10 s electrons/cm
was associated with an energy E >_ 1 kev. These data should about
three.
in the range e-E/S ._
been
Using 1-40
electrons
these key (cm
For the energy obtained from
et al. (1963).
While
can
O'Brien 2sec
values
be
deduced.
an
equivalent It is found
invariant
electrons Taylor
(1964)
greater
than
stated 40 key
electrons to a factor
electron to be
lati-
of energy
n(E)
of of
spectrum = 7.8 • 107
key) -I .
values 40 and Z50 key the Alouette measurements the
and
of energy
at an
flux of 4 erg/cm 2 sec for be considered as accurate
two
2 sec
cone
measuring
flux
above
40
78
key
similar average reported by had
its
maximum
fluxes have McDiarmid at
an
invariant latitude of 65 degrees, the flux above 250 key was maximal at about 60 degrees. McDiarmid et al. (1963) did not present any details for the latitudinal variation of this latter integral flux. By applying a rough correction factor of 0.i for the latitude variation of the average flux above 250 key from 60 to 65 degrees invariant latitude the following approximate equivalent spectra for the energy range 40-250 key can be derived for two ranges of magnetic activity in the auroral zone, if isotropy is assumed for the upper hemisphere: Kp
4:
n(E)
=
l .Z
n(E)
= Z.4
•
10 4
e -E/41
electrons
(cm 2 sec
key)-1
•
l0 s
e -E/3°
electrons
(cm
kev)-1
2 sec
P
(cf.
Hultqvist,
large
and
As
1964b). the
mentioned,
There
is
with
O'Brien,
1964). (O'Brien,
given
above
fluxes.
With
sity
produced defined
not
identical
for
electron
the
the
average only
Observed
The
or from ditions
Into of
is
much
in
passing
launchings with no auroral
in
measured
energy been
on
Spectra
less
made
be
fluxes
are
electron
den-
density of
the
shown
the
measured may
electron
is
averaging
is
ionospheric
that
the
average
can
satellites
of
spectra of
integral
method
values
precip-
be
expressed
(Hultqvist, are
available
average
flux
1964b). one to
has
these
ex-
Protons
Atmosphere
observations
of
than
through
flux
of
averages
electrons
relation for done above.
Energy the
be
significant
average
measuring
precipitated
1963;
equivalent of
the
this
however,
which al.
number
average
and
integral
and
number
atmosphere observed
has
Fluxes
Precipitated
the
fluxes
experimental as
can,
by
integral two
to fit a two-parameter perimental data,
3.
it
produced
The
process, made
the use
in
no
flat.
variable.
intensity
average is
influx.
averaging
instance,
density
Since
particle
be
a large
l0 s the
interest
very et
the
which
whether
the
averaging
with
on of
to on
too too
steepness
McDiarmid
or
over
a factor
when
the the
averaging made
the
seems
angle
than
are
in
1962;
there
questionable
use
by
al.
probably
rather
electrons
pitch
been of
also
to
by
absorption, in
is
values
then
has
a variation It
best
hand on
is
steep
variation et
The
based
too
precipitated
other
1964). are
questioned. the
the spectrum
correction
thus
latitude (O'Brien
On the
latitude are
of
important
latitude
of
itation
spectra
an
increases
applied
spectra
the also
dependence
The
resulting
that
protons for
aurora
under information
or quite
their
electrons. close
disturbed available,
79
on
way Some
to
distinct are
down rocket auroral
upper atmosphere collected in
into
the
results forms, Table
conZ.
While case
electrons
of no.
flights
la, protons
ib,
electrons
were
c,
and
were
amounts. and
show.
This
may
possibly
the
atmosphere.
field lines the
and
Z in which of the
greater
of that
say,
could,
flux,
is as
the
spread
basis
mostly
of
ground
diffuse
and
standard
ground
tribution
of
There
are
two
relations
between
discussed
here,
(1964). on
that
i/5
of the
Dalgarno,
I/5
of
normal
the or
l
energy
more,
as
the
to
for
height
Rocket
measurements be
Electron
and
those
to compare
flux
the
on
electron
these
things
emissions
of
are with
the
height
dis-
valuable.
(1960) results
and
of the
emission
their
aurora.
protons
determination
reported photon
and
ordinary the
Precipitation
of McIlwain
energy
measurements.
than
unsuitable
possi-
heights
judge
hydrogen
radi-
about
same
Injun
surface
would
in
energy
auroral as
difficult
auroral The
an
the
above
measurements
did not use the
any
filter,
transmission light was
to an emission fraction
before
of Tables
quantitative
which and
will be
O'Brien
with
what
and
Taylor
is expected
grounds.
Mcllwain over
also to the
out
the
the
precipitation namely
It is of interest
theoretical
grated
direct
basis
larger
seems
Between Aurora
in
that
generally
locked
1964}.
especially
emissions
Relations Emission
Taylor,
well
observations,
hydrogen
in
electron
any constituent
with
the
a much It
therefore
found to have
measured,
with
the
weak,
techniques.
the
Quantitative Photon
on
emissions over
an
spread
not measure dominant
and
above
quite
above.
up
of magnitude,
protons/cm2sec
excluded
out
were
orders
Injun 3 did were not the
stopped be
seems
no
emissions
In all cases
electrons/cm2sec
hydrogen
mentioned
protons
were
it is not
be
In the
and
flux.
many
be be
however,
generally
4.
were
thus
taking
1958).
(O'Brien
there
expect
could,
1 and
ions)
atom
in the
volumes.
hydrogen
flux may
two
energy
as
would
would
They
and
about
were
not
protons
one
was
Injun electrons
however,
Such
on
as
a neutral
particle
penetrability
there
to protons
As
(Shklovskii,
the proton
a given
kev,
the
heavier
the
form
penetrated
precipitation that
auroral
larger
was
due
electrons
The satellites in which the
bility 40
both
electrons
than
ation
and
be
atmosphere
flux
proton
the
much
form
(and/or
character
outside
reaching
event
The
within
over
auroral
protons
diffuse
magnetic
only
found
no
recorded,
appreciable
well
were
d, when
wide
spread
observed
rate is fairly
1964)
and
curve {}
h.3914
of about
A,
but
measured
of the the
measured
3 kilorayleigh
arbitrary, is probably
but
8O
photon
flux If we
by
reasonable less
than
inteassume
flux corresponds
at this wavelength.
it seems
in error
the photon
photomultiplier.
(cf. a factor
The e.g. of Z and
1/2, respectively, measured electron sec
if the
for an ordinary flux corresponds
spectrum
obtained
auroral-zone to an
was
energy
extrapolated
aurora. flux
McIlwain's of 20 erg/cm
to E = 0.
Thus,
(1960) 2
the
O
resulting electron energy rate is 7 ergs crn -2 sec O'Brien
and
of Z (+_.5) kR auroral zone.
Taylor
average
sec -landan
average
values to get
have
ergs
the
sec'l
zation
as
energy
this.
kR.
(1963)
It has been cross section
cross
section
of
k3914
average
A emission
k3914
_
flux
40
to a factor with that
intensity
key
from
in the gave
of 4.
this
the is
1 kev
down
does one processes?
expect
Dalgarno
shown for the
to E = 0 and spectrum, give 2.5
in measurements
on the basis Omholt (1957,
(1964),
among
others,
of existing 1959) Chamberhave
dis-
at
least
up
to 200
ev
energy
and
has an energy of 3.2 into 3914 A radiation
_ sec,
(1964) has used find the energy agreement (1960) the
if the the flux
between and
O'Brien
uncertainties
ev, is
the
has
over the whole energy pairs are produced expended by fast electrons
in nitrogen per electron ion pair is 35 ev (at least for energies a few hundred ev; it is assumed the figure is correct down to zero we find that 50 x 35 = 1750 ev is dissipated per 3914 _photon.
erg/cm
In would
by Stewart (1956) that the ratio between + _3914 _ band of_I 2 and the total ioni-
is constant
energies of the fast cies must decrease 1964). 1 kR of 3914
,
agreement.
the value 0.02. Assuming that this value is true range of interest, one finds that 50 electrons-ions for each 3914 /_ photon. Since the mean energy
each photon is converted
-2
sec-'
of about three. of Mcllwain one
uncertainties
a good
10Scm
cm -2
Using the =_l_l"-'_lv,_e,,_-+_,_,,,,_,,_,_+_1 E > 0. Thus the Injun 3 results
Considering
and
above
E _>1 kevofabout4ergs
spectrum
flux per kR the emission
Rees
for
accurate comparable
of evaluation,
energy about
(1961),
cussed excitation
per
method
What knowledge lain
the
unit
an
electron
the total energy flux. 5 ergs cm -2 sec -1 for
cm "2
and
reported
flux
they consider a value directly
per
of the latitude distribution i.e. before the electron measurements
of the
energy
to extrapolate
evaluate we find
(1964)
at the maximum As mentioned
a corresponding which order
flux required per kR.
the efficiency 1.80" 10 "_
down to energy) Since
with which energy When the initial
electrons fall below perhaps 100 ev, these efficiensharply (Dalgarno and Griffing, 1958; Dalgarno, O Aphotons corresponds to an energy influx of Z.8 efficiency
figure
1.8"10
-3
is employed.
value 1 • 10-3. requirement
With this conversion to be 5.1 erg cm -2
these
and
and in the
values Taylor analysis
(1964) are
the is taken
experimental much into
better acco_ut.
Dalgarno
efficiency sec -1 per ones than
we kR.
The
of McIlwain expected,
when
The any
total
energy
lain,
efficiency
1961).
only
while
Taylor,
1964).
5.
Relation
of
into
about
the in
ago,
was
large
storage
belt, and
by
in the
has
loss
only
been
(196Zb)
outer
hours.
Similar
x-ray
measurements
(cm I00
zone
are
precipi-
(cf.
than
I000
O'Brien
et al. (1962)
and
at the beyond
in the field tube
same L
e.g.
the particles
in half
et al. orders have
196Z, an
used
a second,
seconds.
82
burst
but
by
but
in
the
Injun
i.
He
of electrons evaluated
et al.,
1964).
above
observed
in
from
Anderson,
of magnitude been
up
electrons
empty
and
1 fluxes
1964).
stopped
been
1962
Winckler
electron
have
of Injun
observed
also
investi-
of x-ray
Anderson,
drain
have
2 sec)
Laughlin,
would
as
assumed
the
of the trapped
_ 2 would
several
ergs/cm
results
was
of
radiation.
through
studies
source
ob-
in the
to be
of the trapped
rate
Winckler
rates
processes
is necessary
recently,
lifetimes
recorded
2 sec) -I , a flux which
independent
lifetime
as, for particles
perhaps
et al., 1962;
the through
plasma,
of trapped
of balloon
years
from
magnetosphere
number
that the
two
dumped
solar
of the measuring
the
rates
the
the
trapped or
the precipitation
a number
average
precipitation (more
particles
of
(O'Brien
the
one
to allow
existence
(Winckler
operated
in
changed
1964)
and
to replenish
the
estimated
that the
Winckler
a value I%
that
were
by
of which
belt assuming
a few
1961;
and
completely
through
found
et al.
electrons
prevailing
The
large
required
atmosphere
mechanisms
average
the
particles
weak
(1962b,
also
radiation
Sometimes
Outer
of
(cf. Chamber-
towards
elsewhere
caused
the occurrence
O'Brien 3 and
lower
outer
point
particles
effects
for understanding
O'Brien the
into photons basis
measurements
the
was
precipitated
acceleration
picture
and
which
disturbances.
with
and
Injun
auroras
sufficiently
radiation
gations
to
trapped
magnetic
injection
and
the
energetic
to be
case
rocket
3 results
between
belts,
that
to occur
This
in
radiation of
the
in any
his
Injun
relations
of disturbing
thought
served
the
roughly
example
from
energy
on theoretical
Electrons
atmosphere the
the influence
was
particle I%
Belt
idea
radiation
found
Precipitated
Radiation
about
preliminary
and
tated
to be
McIlwain
0.2%,
The
of converting
is expected
the
(Krasovskii 196Z).
Thus
1011
electrons
reaching
the total energy yet it persisted
of trapped for
about
O'Brien creases
(1964)
when
would
be
expected
atmosphere. and
change
Taken are
such
of
be a
than
10%
energy tron
one when
above flux
this
new
above
of
trapped
of
radiation
diminishing,
were
simply
seems
to
in-
which
dumped influence
into
the
precipitated
can it the
act
with not
evidence
full
is key
aurora
more
strength the
changes
three
83
due
the whole
Mev
trapped the
orders
This (in electrons electrons
precipitated of
simply
spectrum.
ionization into
quickly of
40
.L-._.=,.L_.e
ionospheric
involved.
very
of
be
ob-
above
in the geomagnetic
electrons
flux for
and
than
not
over
and be
i. 5 Mev
demonstrates
of trapped
a hundredfold, is
u_e,_j:xy .......
change
than
is
precipitation
of energy
could
active
must
simultaneous
greater
a decrease
be
dumping
should
key 40
through
would
(< i0%)
of electrons
precipitation
mechanism
and
that the precipitation
significant
of energy
produce
simple
that
no
burst
point
which by
40
was
that the
acceleration
second)
flux
demonstrated
of a strong
together,
An
has
There
a mechanism
produced
phere.
particles
flux of electrons
electrons
not
must
(1964)
of the mirror
precipitated
the instead
mechanism
demonstrates
since
that place
simultaneously,
middle
to a lowering field,
acceleration
in the
This
shown
trapped
dependent.
in the
key.
the
O'Brien
energy
served
also
takes
particles
Finally, or
if
An
trapped
highly
has
precipitation
magnitude.
the
atmos-
mechanism a fraction more of elec-
Table Precipitated
1 Electrons
60_R
84
Table
Flu,
(ol.o+,
I (Continued)
Villbllmm
m, ot_l_we) plot,
Ho
o+ mol.. 4_.m+b.
R,_ _l_c_e_
_ I_2_
_
0t_
I+(E_
_Mt
151_ UT
_p
.+._l+ ) _130 UT
(cm2 l_
2105
T_
,tw) -I
_l
1/4 _
I/3
oflr_ clrcll;
i.
C_ml.
o(
wlm
N (E) (-E/25 * 5) _d Hp
I
with d_,_b
N (E).._p (-E/_*3)
E>
(1963)
10k_
'
iK E>
,+.@'1 10_..
A_
_lu.
_
(-E/4) E> 10k+v
Aln_llk+tlield I_I ,mell. il
0721 UT LT-_
l+me
+O_
_k,+
_,poml w._,;ol
_
_+.ol. i+_cu
2+6.10_ (cm_ ,_ +or E > 250 k..
,_)-I
c_-
E_+v.
_-
m
,l_+m.m A_ °
_ 0+
_
N(>E)_4 .-E/_o .I
K_ • 4" o
+10 a (+.,_
A =65"
_
O+3 _g (_.Z +_)-I
N(>E) _4.4. 1011.E-_ 9 .I
,_,. k_)-I
(_o+ 40
4 ÷
E < 2_0
k.v)
•_-+
_
E > 4O k_
=m-_
s_ +1 Iw
,_ E)=I+4+ 10+ £-1_ ._.
I%
_p+t
oi,
M,o_. 10 | +l/cm 2 .+c s,_
,, .I+
(I_)
M+_. olm_.
6+10+ .I/era
iK-I
I
-_
v,=
_q
,..,.o.
zR
,
I
•
,
_.-= '°"
I
*
:
I
•
"
•
|
ii
O
|
':'
':;1!
, ,,,,
";'1
!i
II • " - .,I:." ' :. t .;.i: •
.._
:
ill
|
"I'::;" 1
'
I ,:,"
: .l
• "'i
I '
'
/
42
44
41
L-/ DETECTA_: IUTY 55"
34
a8
14
S
2
I
THRES,HOLD
60"
65"
70"
75"
INVARIANT LATTITUDE A (L COS2 A • I) o
Fig. aged
4.4-Intensity over
4
of 3914 sec
A auroral
at half-integral
about fifty passes of Injun 3 early O'Brien and Taylor, 1964.)
light values in 1963.
averof L in (After
I
107!-
INJUN ]][ COMPARISONOF LATITUDE PROFILES OF PRECIPITATED ELECTRONS El
mq-i If_s :r
,%
" ,o.-i!1
J _'_'_
,_
-
II
,,; . : I1
#
_,o- _ il _ , _
li
_1o31--
"J"
_
It M
"
! /v_ /
"_,.,_,_u:r.uulx. _, im
-
I ;I
_
,_-