Evaluation of satellites total ozone retrievals using the NDACC-SAOZ UV-Vis Network

Among the main objectives of the Network for Detection of Atmospheric Composition Changes (NDACC) are the validation and assessment of possible biases between long-term series of data provided by various satellite instruments. Recently, the full series of SAOZ UV-Vis total ozone measurements in the visible Chappuis bands has been revised according to spectral analysis and Air Mass Factor (AMF) settings recommended by the NDACC UV-Vis Working Group (Hendrick et al., 2011). In contrast to Dobson and Brewer systems usually used for satellite validation, SAOZ instruments are insensitive to stratospheric temperature variations and can accurately measure ozone columns during twilight conditions at polar latitudes. In this study performed in support of the ESA Ozone CCI project, measurements from ten NDACC/SAOZ stations available at all latitudes since 1988 have been used for evaluating a series of recent satellite total ozone data products from the TOMS, GOME, SCIAMACHY, OMI and METOP-GOME-2 sensors. Results point to systematic differences that have been attributed to (i) stratospheric temperature and solar zenith angle (SZA) dependences in the satellite retrievals, (ii) longitudinal modulations and seasonal variations of tropospheric ozone columns not accounted for in the ozone profile climatology used for calculating the AMFs of both ground-based and satellite data, and (iii) remaining uncertainties on the climatological stratospheric ozone profiles in polar winter conditions. For those measurements mostly sensitive to stratospheric temperature like TOMS, OMI-TOMS or to SZA like SCIAMACHY-TOSOMI, the application of temperature and SZA corrections resulted in the almost complete removal of the seasonal difference with SAOZ, improving significantly the consistency between satellite and ground-based total ozone series