Tropical tropopause parameters derived from GPS radio occultation measurements with CHAMP

Abstract

The temperature structure in the tropical upper troposphere and lower stratosphere (UTLS) region is discussed based on Global Positioning System (GPS) radio occultation (RO) data from the German CHAMP (CHAllenging Minisatellite Payload) satellite mission. Several climatologies for tropopause parameters based on radiosonde data and model analyses have been published in recent years. Both data sources suffer either from low global coverage or poor vertical resolution. The GPS RO technique, on the other hand, is characterized by global coverage, high vertical resolution, all‐weather viewing, and long‐term stability. CHAMP RO data are available since February 2001. Since May 2001, up to 200 high‐ resolution temperature profiles per day are available. The temperature bias between CHAMP temperature profiles and radiosonde data as well as ECMWF analyses is less than 0.5 K between 300–30 hPa. On the basis of the May 2001 to November 2003 data set of CHAMP RO data the structure and temporal and spatial variability of the tropical tropopause based on several tropopause definitions (thermal and cold‐point tropopause) are discussed. This includes an overview of the global tropopause characteristics, the discussion of the annual cycle and the latitudinal‐longitudinal structure of the tropical tropopause. In the CHAMP RO temperature data, clear evidence of the stratospheric quasi‐biennial oscillation (QBO) was found. The goal of this study is to show the potential of GPS RO for global monitoring of the temperature demonstrated exemplarily for the tropical UTLS region and based on the first 31 months (as of November 2003) of CHAMP RO data.