The atmospheric limb sounding technique making use of radio signals transmitted by the Global Position System (GPS) has emerged as a promising approach for global meteorological observations. As demonstrated by the proof-of-concept GPS Meteorology (GPS/MET) experiment and more recently by the CHAMP and SAC-C missions, the GPS radio occultation sounding data are of high accuracy and high vertical resolution. In late 2005, the joint U.S.-Taiwan COSMIC mission will be launched and is expected to collect up to 3,000 radio occultation soundings per day. These data will be available in near real-time for global weather analysis and prediction. The COSMIC data will also be valuable for climate monitoring and ionospheric research.

Radio occultation measures phase and amplitude of the microwave signals emitted from GPS. These signals are inverted to obtain profiles of signal bending, atmospheric refractivity, pressure temperature and water vapor. The main purpose of the upcoming COSMIC mission is to demonstrate the value of these radio occultation products for weather forecasting, climate monitoring, and space weather studies. This presentation will provide an overview of the COSMIC program, and its applications to weather and climate. For further information on COSMIC, please refer to http://www.cosmic.ucar.edu/.