The German research satellite CHAMP (CHAllenging Minisatellite Payload for geoscientific research) continuously records about 220 radio occultation (RO) profiles per day since March 2002. The mission is expected to last at least until 2007, thus CHAMP radio occultation (RO) data provide the first opportunity to create real RO based climatologies on a longer term. CHAMPCLIM is a joint project of the Institute for Geophysics, Astrophysics, and Meteorology (IGAM) in Graz and the GeoForschungsZentrum (GFZ) in Potsdam. It aims at exploiting the CHAMP RO data in the best possible manner for climate research. For this purpose, all CHAMP RO profiles provided by GFZ on excess phase level (GFZ level 2, ~180 profiles/day) are currently processed at IGAM to obtain atmospheric profiles of refractivity, geopotential height, and dry temperature. The IGAM retrieval scheme is focused on minimizing biases and yields a new atmospheric data set especially tuned for monitoring climate variability and change. The atmospheric profiles (~150 profiles/day) are used to create climatologies on a monthly, seasonal, and annual basis by two different techniques: On the one hand by standard averaging-and-binning techniques, on the other hand, by 3D-variational assimilation of RO refractivity data into ECMWF analysis fields, yielding global climate analyses on a denser horizontal grid. After optimizing the RO data processing for climate applications and validation of the retrieval results using various reference data sources (on-going), the main emphasis is now on operational issues, processing of the 2002-2003 data, and on the creation of climatologies including error estimates. After a short overview on the status of the CHAMPCLIM project, which shall set the scene for other CHAMPCLIM-related presentations during this conference, we will focus on direct dry temperature climatologies from the summer season (JJA) 2003, obtained by averaging-and-binning. Our results show that useful dry temperature climatologies resolving horizontal scales > 1000 km can be obtained even with data from a single RO receiver. RO based climatologies have the potential to improve modern operational climatologies, especially in regions where the data coverage and/or the vertical resolution of RO data is superior to traditional data sources.

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Foelsche, U.; Gobiet, A.; Steiner, A. K.; Borsche, M.; Wickert, J.; Schmidt, T.; Kirchengast, G. (2006): Global Climatologies Based on Radio Occultation Data: The CHAMPCLIM Project. - In: Foelsche, U.; Kirchengast, G.; Steiner, A. (Eds.), Atmosphere and climate : studies by occultation methods, Springer, 303-314.