Sunday, 9 January 2005
Monitoring Temperature Trends in Antarctica Using GPS Radio Occultation
In late 2005, the US-Taiwan joint satellite mission known as the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) will launch six Low Earth Orbit (LEO) satellites. These satellites, each equipped with an advanced Global Positioning System (GPS) receiver, will use Radio Occultation (RO) limb sounding technology to profile the Earth's atmosphere with unprecedented accuracy and vertical resolution. The GPS RO soundings available from COSMIC will make significant contributions to global weather prediction, ionospheric research, and climate monitoring. The GPS receivers will measure the phase and amplitude, deduce the bending angles as a function of height, and lastly obtain vertical profiles of refractivity using the Abel inversion under the local spherical symmetry assumption. To demonstrate the potential value of GPS RO data in climate monitoring, we analyzed GPS RO data obtained from a recent single-satellite German mission, known as the CHAllenging Mini Payload for Geophysical Research and Application (CHAMP). This study examined the monthly mean temperatures over the Antarctic using the CHAMP GPS RO data, provided by UCAR's COSMIC Data Analysis and Archive Center (CDAAC), from June 2001 through present. Seasonal and annual variations of tropopause temperature and altitude were analyzed, as well as the cooling/warming trends in the troposphere and stratosphere. These trends and variations were compared against similar analyses derived from the radiosonde data and the ECMWF and NCEP global analyses. Results show that GPS data can be used to assess the accuracy of global analyses and radiosonde data and its usefulness in climate monitoring.