GPS radio occultation with CHAMP and SAC-C: Global monitoring of thermal tropopause parameters

Abstract

In this study the global lapse-rate tropopause (LRT) pressure, temperature, potential temperature, and sharpness are discussed based on Global Positioning System (GPS) radio occultations (RO) from the German CHAMP (CHAllenging Minisatellite Payload) and the U.S.-Argentinian SAC-C (Satelite de Aplicaciones Cientificas-C) satellite missions. Results with respect to seasonal variations are compared with operational radiosonde data and ECMWF (European Centre for Medium-Range Weather Forecast) operational analyses. Results on the tropical quasi-biennial oscillation (QBO) are updated from an earlier study. CHAMP RO data are available continuously since May 2001 with on average 150 high resolution temperature profiles per day. SAC-C data are available for several periods in 2001 and 2002. In this study temperature data from CHAMP for the period May 2001-December 2004 and SAC-C data from August 2001-October 2001 and March 2002-November 2002 were used, respectively. The bias between GPS RO temperature profiles and radiosonde data was found to be less than 1.5 K between 300 and 10 hPa with a standard deviation of 2-3 K. Between 200-20 hPa the bias is even less than 0.5 K (2 K standard deviation). The mean deviations based on 167 699 comparisons between CHAMP/SAC-C and ECMWF LRT parameters are (-2.1±37.1) hPa for pressure and (0.1±4.2) K for temperature. Comparisons of LRT pressure and temperature between CHAMP and nearby radiosondes (13 230) resulted in (5.8±19.8) hPa and (-0.1±3.3) K, respectively. The comparisons between CHAMP/SAC-C and ECMWF show on average the largest differences in the vicinity of the jet streams with up to 700m in LRT altitude and 3 K in LRT temperature, respectively. The CHAMP mission generates the first long-term RO data set. Other satellite missions will follow (GRACE, COSMIC, MetOp, TerraSAR-X, EQUARS) generating together some thousand temperature profiles daily. © 2005 Author(s). This work is licensed under a Creative Commons License.