Use of radiances data in ERA-40 Graeme Kelly ECMWF, United Kingdom At ECMWF a re-analysis has been completed using all available satellite and conventional data from 1967 to 2002. A reduced resolution version of the ECMWF operational IFS system (3D-VAR at 60 levels and horizontal resolution of TL 159 (120 km) was used for the data assimilation system. The use of satellite radiances started with VTPR radiances in 1973 and radiances were used directly in the assimilation from VTPR, HIRS, MSU, SSU, and AMSU. SSMI radiances where input to a pre-processing 1D-VAR and the retrieved products of total precipitable water and wind speed were then assimilated in the 3D-VAR analysis. Some of the difficulties that arose with the satellite data during the re-analysis discussed. The reanalysis was highly successfully but it is clear that further re-analyses could be further improved with the knowledge obtained from ERA40 about the performance of the satellite sensors.