Abstract. GPS radio occultation (RO) has been recognised as an alternative atmospheric upper air observation technique due to its distinct features and technological merits. The CHAllenging Minisatellite Payload (CHAMP) RO satellite and FORMOSAT-3/COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate) RO constellation together have provided about ten years of high quality global coverage RO atmospheric profiles. This technique is best used for meteorological studies in the difficult-toaccess areas such as deserts and oceans. To better understand and use RO data, effective quality assessment using independent radiosonde data and its associated collocation criteria used in tempo-spatial domain are important. This study compares GPS RO retrieved temperature profiles from both CHAMP (between May 2001 and October 2008) and FORMOSAT-3/COSMIC (between July 2006 and December 2009) with radiosonde data from 38 Australian radiosonde stations. The overall results show a good agreement between the two data sets. Different collocation criteria within 3 h and 300 km between the profile pairs have been applied and the impact of these different collocation criteria on the evaluation results is found statistically insignificantly. The CHAMP and FORMOSAT-3/COSMIC temperature profiles have been evaluated at 16 different pressure levels and the differences between GPS RO and radiosonde at different levels of the atmosphere have been studied. The result shows that the mean temperature difference between radiosonde and CHAMP is 0.39 • C (with a standard deviation of 1.20 • C) and the one Correspondence to: E. Fu (f.fu@bom.gov.au) between radiosonde and FORMOSAT-3/COSMIC is 0.37 • C (with a standard deviation of 1.24 • C). Different collocation criteria have been applied and insignificant differences were identified amongst the results.

GPS radio occultation (RO) has been recognized as an alternative atmospheric upper air observation technique due to its distinct features and technological merits. This technique is best used for meteorological studies in remote and/or difficult-to-access areas such as the Polar Regions. The CHAllenging Minisatellite Payload (CHAMP) space mission has provided about eight years of high quality global coverage atmospheric profiles. This study first evaluates the accuracy of CHAMP RO retrieved temperature profiles in the Antarctic region by using radiosonde data. Different collocation criteria have been applied. The overall results show a good agreement between the two data sets. Utilizing seven completed years of CHAMP temperature profiles, the study then investigates seasonal temperature trends at 100 hPa and 500 hPa pressure levels in the Antarctic region. Detailed temperature variations in both spatial and temporal domains are revealed and their implications for climate change are discussed