Evaluation of Satellites Total Ozone and NO2 columns retrievals using the NDACC-SAOZ UV-Vis Network
Résumé
Among the main objectives of the Network for Detection of Atmospheric Composition Changes (NDACC) are the validation and eventually the correction of biases between long-term series of data provided by various satellite instruments. This presentation deals with the evaluation of satellite total ozone retrievals using observations performed by the NDACC/SAOZ UV-Vis spectrometers at all latitudes since 1988. Recently, the full series of SAOZ total ozone measurements in the visible Chappuis bands has been revised according to the spectral analysis and Air Mass Factor (AMF) settings recommended by the NDACC UV-Vis Working Group (Hendrick et al., 2011). The comparison involves overpass observations from the TOMS, GOME-GDP4, SCIAMACHY-TOSOMI, SCIAMACHY-OL3, OMI-TOMS, OMI-DOAS and METOP-GOME-2 satellite instruments. Significant improvement is obtained after applying the new O3 AMFs, although systematic seasonal differences between SAOZ and all other instruments still remain. These are shown to originate from (i) stratospheric temperature and solar zenith angle (SZA) dependences in the satellites retrievals, (ii) longitudinal modulations and seasonal variations of tropospheric ozone columns not accounted for in the ozone profile climatology used for calculating the AMFs, and (iii) 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 results in the almost complete removal of the seasonal difference with SAOZ, improving significantly the consistency between satellite and ground-based total ozone series. However, small but sometimes signi cant biases still remain after applying those corrections. A similar exercise is in progress with SAOZ NO2 data sets, using AMFs calculated from a profile climatology based on HALOE, SAGE II, POAM III and SAOZ balloon profiles. The consistency with GOME/ERS2, SCIAMACHY/ENVISAT and OMI/AURA NO2 total columns is currently examined. In this presentation, we will focus on the resulting evaluation of ozone and NO2 total columns biases, temperature and SZA dependences of the various satellite instruments.