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Introduction

The ozone total column has been measured in the last decades employing ground based as well as satellite instruments. Comparison of the general trends of both series of data, the first one obtained by TOMS (Total Ozone Mapping Spectrometer) on board of Nimbus 7 and Meteor 3 satellites and the second one with the WMO (Dobson and Brewer) instruments from 1978 to 1994, show a mean decrease in the Southern Hemisphere (25º - 60º S) up to May 1991, before the Mount Pinatubo eruption, of -3.85 % per decade for the satellite data and almost the same, -3.87 % per decade, for the ground based one. For the ozone trends after 1991 the situation is not as clear, giving a rather mean constant behavior from TOMS measurements and a smaller decrease from ground ones (Bojkov et al., 1999).

In the last years, TOMS instruments were placed on board of two satellites, ADEOS (NASDA) and Earth Probe (or EP, NASA), orbiting at different altitudes and consequently having different pixel resolution. Also the GOME instrument on board of ERS-2 (Earth Remote Sensing, ESA) satellite is making systematic measurements of the ozone total column from 1995. In the present work we will intercompare satellite with ground based instruments data. Besides other applications, the present results can be used for analyzing in detail the Southern Hemisphere ozone trends (Bojkov et al., 1999) up to higher latitudes and the contribution of the ozone layer to the attenuation of UVB (280 - 320 nm) solar radiation (Zerefos and Bais, 1997; Herman et al, 1999; Herman et al, 2000).

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