Potential contribution of CHAMP occultation to pressure field improvement for gravity recovery

Abstract

This paper studies one aspect of use of the CHAMP GPS occultation data, namely the improvement of the atmospheric pressure field, particularly over Antarctica. Previous studies indicate that pressure differences between ECMWF and ground truth data reach 5.18 hPa RMS over Antarctica [Ge et al., 2003]. In this study, comparisons of pressure profiles (January-March 2003) from data (CHAMP occultation and radiosonde) and models (ECMWF and NCEP), indicate large discrepancies over different regions, notably over southern polar region. Global pressure differences between CHAMP and radiosonde and model outputs reach 4 hPa RMS at 1 km above MSL. We found a positive bias in CHAMP data (CHAMP measures larger pressure values) when comparing with both radiosonde and ECMWF. Analysis shows the lack of adequate penetration of CHAMP occultation data in the planetary boundary layer particularly in the tropical region (only ∼10% signal is within 1 km above MSL), as compared to ∼80% penetration in Arctic and Antarctica. However, CHAMP provides improved data coverage in temporal, spatial and vertical resolution globally. We conclude that the CHAMP occultation data could potentially improve the surface pressure modeling to benefit temporal gravity recovery, in particular over data sparse region such as Antarctica. © 2005 Springer-Verlag Berlin Heidelberg.