seasonal variability in local-noon UV Index and the ...

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(UVI), cloud modification (CMF) and aerosol correction (Ca). ⇒ Deviations on UVI estimates by using dynamic aerosol from. OMAERUVd instead of aerosol ...

Ten years of OMI surface UV: seasonal variability in local-noon UV Index and the main contributing factors behind it W. Wandji1, A Lipponen1, M. Pitkänen1 , O. Torres2, N. Krotkov2, J. Tamminen3 and A. Arola1 1Finnish Meteorological Institute, Kuopio, Finland. 2NASA Goddard Space Flight Center, Greenbelt, MD, USA. 3Finnish Meteorological Institute, Helsinki, Finland.

I. Introduction Since the launch of the NASA Aura satellite on July 15, 2004, the Dutch–Finnish Ozone Monitoring Instrument (OMI) on board the satellite has collected more than 10 years of data. The present study investigated the variability of OMI observations focusing on local-noon UVI and UV–absorbing aerosol optical depth over the time period from December 2004 to November 2014. Long-term monthly and seasonal means, and their corresponding yearly anomalies (departures from the long-term mean), were computed and analyzed globally. The main objective was to assess the causes for enhancement or reduction in surface UV levels that are persistent enough to induce significant monthly or seasonal impact, the possible factors being total column ozone, cloud attenuation or absorbing aerosols. The total column ozone and cloud attenuation effects are taken into account in the operational OMI surface UV products on a “measurement-bymeasurement” basis, while the correction for absorbing aerosols is based on monthly climatology. Since, the monthly climatology does not capture the inter-annual variability in absorbing aerosols, we assessed separately the potential influence of absorbing aerosols similarly in monthly and seasonal UV levels by utilizing absorbing aerosol optical depth from OMAERUV product

III. Results rLPSA of clear sky UVI in summer (JJA)

mainly ozone influence

rLNSA of CMF in summer

relative monthly anomaly of CMF in June 2013 over India with summer monsoon

rLNSA of (Ca) in summer

relative anomaly of (Ca) in SON 2008

II. Method OMI UV products: OMUVBd, OMAERUVd


 Monthly, seasonal, long-term means and anomalies of UV Index (UVI), cloud modification (CMF) and aerosol correction (Ca)  Deviations on UVI estimates by using dynamic aerosol from OMAERUVd instead of aerosol climatology in operational algorithm

2010 wildfires in Russia 2008 strong negative AOD anomalies reported

OMAERUVd UVI minus operational UVI in JJA

IV. Conclusions and perspectives  Depending on the season, absolute relative anomalies are mostly less than 7% for clear sky UVI, 10% for CMF and 2% for Ca  Noticeable anomalies are related to unique events occurring over a limited time period like ozone depletion, El Nino event or monsoon and dust outbreak or wildfires affecting clear sky UVI, CMF and aerosol correction respectively.  Using OMAERUVd product instead of aerosol climatology leads to significant differences on UV estimates close to 2 UVI units  Assessment is under way to study the possibility to produce a new aerosol climatology for accurate UV estimates by the means of AERONET information

OMAERUV Operational aerosol climatology

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