ASSIMILATION OF POLAR WINDS AND RECENT SATELLITE WINDS IMPACT STUDIES AT ECMWF

January 2003. Their optimal use is an ongoing issue especially when combining the wind products of both polar-orbiting satellites (Terra and Aqua) that carry Modis instruments. Very recently Polar Modis winds became available from NOAA/NESDIS. They show better agreement with the ECMWF model background compared with winds produced at CIMSS. In several assimilation experiments the observational error has been reduced in order to take into account the improved quality of the winds. This leads to more consistent analyses over the Poles, in particular when AMVs from Terra and Aqua are used. In general, the neutral to slightly positive forecast impact of Modis winds in 3DVAR low-resolution experiments remains over both hemispheres. None of the Modis experiment is clearly outperforming in terms of forecast scores, although the usage of Aqua and Terra Modis winds has an advantage over Southern Hemisphere. We also present some of the most recent Global Observing System Experiments (OSEs) carried out at ECMWF. These show a positive impact of the satellite derived AMVs in the ECMWF system. The strongest impact is over the Tropics and Southern Hemisphere. 1