Comparison of CHAMP Radio Occultation Climatologies of the UTLS to Operational ECMWF Analyses and Forecasts

In recent years radio occultation (RO) data have become an integral part of monitoring the atmosphere because of their high vertical resolution, high precision (<0.5 K), and inter-comparability between different satellite missions. Data from the CHAllenging Minisatellite Payload (CHAMP) satellite are now available for more than six years providing the first opportunity to create RO based climatologies. We present temperature climatologies and systematic differences of selected seasons compared to operational analyses of the European Centre for Medium-Range Weather Forecasts (ECMWF). In general, we find good agreement with systematic differences below 0.5 K. Exceptions are: altitudes above 30 km, where CHAMP climatologies are about 1 K warmer than ECMWF analyses; the austral winter polar vortex where deviations of more than ±3.5 K exist; and the tropical tropopause region which is up to 2 K colder in the ECMWF analyses until the beginning of 2006 due to limitations in resolution of the analyses. Here we present first results of CHAMP climatologies compared to ECMWF climatologies obtained from 24 hrs and 36 hrs forecast files. Within this time the forecasts are expected to have uncoupled from the initial analyses still representing a physically reasonable state of the atmosphere but presumably free of biases of the analysis. In turn, deviations of RO climatologies compared to ECMWF forecasts are expected to decrease considerably. Additionally, since mid-December 2006 RO data of various satellites including the CHAMP satellite are assimilated into ECMWF operational analyses rendering these not anymore independent from RO data. (CHAMP RO climatologies presented for the year 2007 are thus referenced to forecast fields.)