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

[摘要] In this study the global lapse-rate tropopause (LRT) pressure,temperature, potential temperature, and sharpness are discussedbased on Global Positioning System (GPS) radio occultations (RO)from the German CHAMP (CHAllenging Minisatellite Payload) and theU.S.-Argentinian SAC-C (Satelite de Aplicaciones Cientificas-C)satellite missions. Results with respect to seasonal variationsare compared with operational radiosonde data and ECMWF (EuropeanCentre for Medium-Range Weather Forecast) operational analyses.Results on the tropical quasi-biennial oscillation (QBO) areupdated from an earlier study. CHAMP RO data are availablecontinuously since May 2001 with on average 150 high resolutiontemperature profiles per day. SAC-C data are available for severalperiods in 2001 and 2002. In this study temperature data fromCHAMP for the period May 2001-December 2004 and SAC-C data fromAugust 2001-October 2001 and March 2002-November 2002 were used,respectively. The bias between GPS RO temperature profiles andradiosonde data was found to be less than 1.5K between 300 and10hPa with a standard deviation of 2-3K. Between 200-20hPa thebias is even less than 0.5K (2K standard deviation). The meandeviations based on 167699 comparisons between CHAMP/SAC-C andECMWF LRT parameters are (-2.1±37.1)hPa for pressure and(0.1±4.2)K for temperature. Comparisons of LRT pressure andtemperature between CHAMP and nearby radiosondes (13230) resultedin (5.8±19.8)hPa and (-0.1±3.3)K, respectively. Thecomparisons between CHAMP/SAC-C and ECMWF show on average thelargest differences in the vicinity of the jet streams with up to700m in LRT altitude and 3K in LRT temperature, respectively.The CHAMP mission generates the first long-term RO data set. Othersatellite missions will follow (GRACE, COSMIC, MetOp, TerraSAR-X,EQUARS) generating together some thousand temperature profilesdaily.

[学科分类] 大气科学