GPS radio occultation: results from CHAMP, GRACE and FORMOSAT-3/COSMIC.

The Taiwan/US FORMOSAT-3/COS MIC (FORMOsa SATellite mission - 3/Constellation Observing System for Meteorology, Ionosphere and Climate) satellite constellation was success fully launched on 14 April 2006. It is expected to leverage the use of the GPS (Global Positioning System) radio occultation data for atmospheric and ionospheric research to improve global weather forecasts and aid climate change related studies. FORMOSAT-3/COSMIC, together with the European MetOp, German CHAMP and US/Ger man GRACE-A satellites, form a 9 satellite constellation for precise atmospheric sounding on a global scale. This satellite constellation is expected to provide about 3500 occultation measurements daily. Recent results and the status of the CHAMP and GRACE-A orbit and occultation data analysis are reviewed and complemented with a review of initial results from FORMOSAT-3/COSMIC at GFZ. The significantly in creased potential of the CHAMP, GRACE-A and FORMOSAT-3/COSMIC constellation for atmospheric studies, compared to single satellite missions, is demonstrated for selected applications such as global monitoring of water vapor distributions, tropopause parameters and ionospheric irregularities.