Tropical tropopause climatology as observed with radio occultation measurements from CHAMP compared to ECMWF and NCEP analyses

A temperature climatology from radio occultation measurements of the CHAllenging Minisatellite Payload (CHAMP) satellite, comprising five years of measurements from September 2001 to August 2006, was analyzed in the tropical (15 degrees S-15 degrees N) tropopause region. Validation against operational analyses of the European Centre for Medium-Range Weather Forecasts (ECMWF) showed excellent overall agreement except near the tropical tropopause, where systematic differences generally amount to -1 K to -2 K. Validation against tropopause temperatures from the U. S. National Centers for Environmental Prediction (NCEP) reanalyses showed NCEP deviations of about +2 K to +4 K. The ECMWF deviations can be attributed to the lower vertical resolution and weaker representation of atmospheric wave activity in ECMWF analyses. This evidence is confirmed by improved data from February 2006 onwards, where an enhancement of the ECMWF analyses became effective. Initial inspection of extreme tropical tropopause profiles provided evidence that extremely cold tropopause temperatures can reach 100 degrees C.