Evaluation of GOME, SCIAMACHY, GOME2, SBUV, OMI and IASI–METOP total ozone retrievals performances by comparison with SAOZ NDACC ground-based measurements
Résumé
High accuracy global total ozone measurements from space are key data for evaluating the amplitude of ozone depletion, understanding its contribution and consequences on climate change and predicting the future evolution of both ozone and climate. Long series of total ozone data are available, but showing still systematic significant differences between them. Here most recent data available from GOME-ERS2, SCIAMACHY-Envisat, GOME2-Metop reprocessed with the GODFIT V3 (GOME-Type Direct FITing) algorithm developed in the frame of the ESA Ozone Climate Initiative (Lerot et al., 2014), from NASA SBUV v8.6 (McPeters et al., 2013), NASA-AURA-OMI (Levelt et al, 2007) and IASI Metop A and B (Clerbaux et al., 2009), are compared with SAOZ total ozone ground-based NDACC measurements available at several stations distributed in latitude in the world since the early 90’s (Pommereau and Goutail, 1988).
The comparison does show some small mean biases between satellites and SAOZ, as well as between satellites, depending on the satellites observing periods. But most significant is the amplitude of the seasonal variations of the satellite-SAOZ difference varying with the satellite data used varying for example at northern mid-latitude from 2% amplitude with the GODFIT GOME, SCIA and GOME2 data, 3% with SBUV and 4% with IASI. Although the seasonal cycle of stratospheric temperature contributes partly in the case of SBUV measurements in the UV, the largest identified cause of seasonal variation of the satellite-SAOZ difference appears related to a Sun Zenith Angle dependence affecting possibly both satellites and/or ground-based measurements. The origin of this SZA dependence is further explored by looking at the satellite-SAOZ differences at various NDACC stations distributed in latitude.