Assessing the Climate Monitoring Utility of Radio Occultation Data: From CHAMP to FORMOSAT-3/COSMIC

Radio Occultation (RO) data, using Global Positioning System (GPS) signals, deliver high quality observations of the atmosphere, which are well suited for monitoring global climate change. The special climate utility of RO data arises from their accuracy and long-term stability due to self-calibration. Launched in 2000, the German research satellite CHAMP (CHAllenging Minisatellite Payload for geoscientific research) provides the first opportunity to create RO based climatologies. Overlap with data from the Taiwan/US FORMOSAT-3/COSMIC (Formosa Satellite Mission 3/Constellation Observing System for Meteorology, Ionosphere and Climate, F3C) mission allows the testing for consistency of climatologies derived from different satellites. We show initial results for zonal mean climatologies as well as tropical tropopause parameters based on F3C RO data. Our results indicate excellent agreement between RO climatologies from different F3C satellites as well as between data from different RO missions. After subtraction of the estimated respective sampling error, seasonal temperature climatologies derived from different F3C satellites are in agreement to within < 0.1 K almost everywhere in the considered domain between 8 and 35 km altitude. Monthly mean tropical tropopause (lapse rate) temperatures and attitudes derived from four different RO missions show remarkable consistency (< 0.2 - 0.5 K, < 50 - 100 m) and indicate that data from different RO missions can indeed be combined without need for inter-calibration. F3C final constellation sampling error estimation shows a small oscillating local time related error (0.03 K amplitude) in the extratropics.