Based on CHAMP RO phase delay and orbit data (version 2 data set) provided by the GFZ Potsdam (Wickert et al. 2004), atmospheric parameters were retrieved at the WegCenter and a record of more than five years of CHAMP RO dry temperature climatologies has been established with the CHAMPCLIM retrieval version 2.3 (CCRv2.3). A description of the CCRv2.3 and the related quality control is given by Borsche et al. (2006) and Gobiet et al. (2007). The construction of climatologies is described by Foelsche et al. (2008b). We used monthly-mean zonal-mean CHAMP dry temperature climatologies at 10° latitude resolution as a function of pressure up to 2.5 hPa (~40 km) for the time span September 2001-December 2006. An example of a monthly climatology is shown in Fig. 2 (Sect. 3.1). No CHAMP data were available for July 2006 due to satellite problems. In addition, we used RO data from three other satellites as independent "anchor points", i.e., SAC-C for June, July, August (JJA) 2002, GRACE for July 2006, and COSMIC for December 2006. SAC-C (version 2005.3090 data set) and COSMIC (version 1 data set) phase delay and orbit data were provided by the University Corporation of Atmospheric Research/COSMIC Data Analysis and Archival Center (UCAR/CDAAC), Boulder (Rocken et al. 2000; Wu et al. 2005; Schreiner et al. 2007). GRACE phase delay and orbit data (version 2 data set) were provided by GFZ Potsdam (Wickert et al. 2005). The retrieval version CCRv2.3 has been applied to all RO data used in this study ensuring a consistent data set. Possible inhomogeneities which may be introduced due to phase and orbit data stemming from different processing centers are currently under investigation. Regarding synthetic MSU bulk temperatures the implications are estimated to be smaller than the sampling error estimates.
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