ON THE CORRECTION OF THE TOTAL OZONE CONTENT OVER ATHENS, GREECE AS DEDUCED FROM SATELLITE-OBSERVATIONS

The observations with the Total Ozone Mapping Spectrometer (TOMS) moun ted aboard the Nimbus-7 satellite have previously been used to determi ne the trends of the total ozone amount over Athens, Greece (38 degree s N, 24 degrees E), since 1979, for various months (Varotsos, C. A., a nd Cracknell, A. P., 1993, International Journal of Remote Sensing, 14 , 2053-2059). The total ozone depletion over the 13-year time period s howed a strong seasonal variation of the trend from more than 7 per ce nt in winter to about 2.5 per cent in summer. However, the TOMS instru ment measures the back-scattered ultraviolet radiation in order to det ermine ozone content and is limited to observations above the cloud le vel. In the presence of thick cloud the column ozone content is genera lly underestimated. This underestimation of the total ozone amount is quantitatively examined, especially in the synoptic cases where ozone- rich air has been transported into the lower troposphere. The influenc e of this underestimation on the total ozone depletion over Athens, Gr eece, deduced from TOMS observations, is finally attempted.