Climatologies Based on Radio Occultation Data from CHAMP and Formosat-3/COSMIC

Radio Occultation (RO) data using Global Navigation Satellite System (GNSS) signals have the potential to deliver climate benchmark measurements, since they can be traced, at least in principle, to the international standard for the second. The special climate utility of RO data arises from their accuracy and long-term stability due to self-calibration. The German research satellite CHAMP (CHAllenging Minisatellite Payload for geoscientific research) provided the first opportunity to create RO based climatologies over more than 6 years. 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 testing the consistency of climatologies derived from different satellites. We show results for altitude- and latitude-resolved seasonal zonal mean dry temperature climatologies. Our results indicate excellent agreement between RO climatologies from different F3C satellites: After subtraction of the estimated respective sampling errors, differences are smaller than 0.1 K almost everywhere in the considered domain between 8 km and 35 km altitude. Mean differences (over the same domain) are smaller than 0.03 K in any case and can be as small as 0.003 K. Differences between F3C and CHAMP are only slightly larger. The assimilation of RO data at ECMWF (European Centre for Medium-Range Weather Forecasts) considerably improved operational analyses in regions where the data coverage and/or the vertical resolution and accuracy of RO data is superior to traditional data sources.