Climatological validation of stratospheric temperatures in ECMWF operational analyses with CHAMP radio occultation data

Abstract

A climatological validation of the thermal structure of European Centre for Medium-Range Weather Forecasts (ECMWF) operational analyses with a new 2.5-year dataset derived from the CHAllenging Minisatellite Payload (CHAMP) radio occultation (RO) satellite mission was performed. Close overall agreement was found in the 10-30 km altitude region, with seasonal zonal mean temperature biases generally smaller than 0.5 K. Apart from that, discrepancies in the Austral polar vortex region (cold biases up to -2.5 K, warm biases up to +3.5 K) and a cold bias of the analysis at the low-latitude tropopause (up to -2 K) were revealed. The polar vortex bias can be clearly attributed to the ECMWF analysis and data assimilation system and the tropopause bias is strongly indicated to be related to the smaller tropopause variability and the lower vertical resolution in the analysis. The study underlines the utility of RO data as global long-term climate reference datasets. Copyright 2005 by the American Geophysical Union.