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Ann. Geophys., 26, 1965-1975, 2008
www.ann-geophys.net/26/1965/2008/
© European Geosciences Union 2008
Estimation of photolysis frequencies from TOMS satellite measurements and routine meteorological observations
C. Topaloglou1, B. Mayer2, S. Kazadzis1,4, A. F. Bais1, and M. Blumthaler3
1Laboratory of Atmospheric Physics, Aristotle University of Thessaloniki, Greece
2Deutsches Zentrum für Luft- und Raumfahrt (DLR), Oberpfaffenhofen, Germany
3Medical University Innsbruck, Austria
4Finnish Meteorological Institute, Helsinki, Finland
Abstract. A study on the estimation of J(O1D) and J(NO2) photolysis
frequencies when limited ground based measurements (or even no measurements
at all), are available is presented in this work. Photolysis frequencies can
be directly measured by chemical actinometry and filter radiometry or can be
calculated from actinic flux measurements. In several meteorological
stations, none of the methods above are applicable due to the absence of
sophisticated instruments such as actinometers, radiometers or
spectroradiometers. In this case, it is possible to calculate photolysis
frequencies with reasonable uncertainty using either a) standard
meteorological observations, such as ozone, cloud coverage and horizontal
visibility, available in various ground based stations, as input for a
radiative transfer model or b) satellite observations of solar global
irradiance available worldwide, in combination with an empirical method for
the conversion of irradiance in photolysis frequencies. Both methods can
provide photolysis frequencies with a standard deviation between 20% and
30%. The absolute level of agreement of the retrieved frequencies to
those calculated from actual actinic flux measurements, for data from all
meteorological conditions, is within ±5% for J(O1D) and less
than 1% for J(NO2) for the first method, while for the second method
it rises up to 25% for the case of J(O1D) and 12% for
J(NO2), reflecting the overestimation of TOMS satellite irradiance when
compared to ground based measurements of irradiance for the respective
spectral regions. Due to the universality of the methods they can be
practically applied to almost any station, thus overcoming problems
concerning the availability of instruments measuring photolysis frequencies.
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