Tuesday, 16 January 2007: 3:30 PM
Validation of Microwave Sounders' Lower Stratosphere Temperature Trend using GPS RO Data
207A (Henry B. Gonzalez Convention Center)
The detection and validation of long-term upper-troposphere and lower stratosphere (UTLS) temperature trend are critical for global climate study in monitoring ozone depletion and water vapor variation. Onboard the National Oceanic and Atmospheric Administration (NOAA) series of polar orbiting satellites, Microwave Sounder Unit (MSU) has provided data for climate studies since its first launch in 1979. Because MSU measurements, which are in the 50 to 70 GHz oxygen band, are not affected by clouds and are directly proportional to the specific atmospheric layer temperatures, MSU data is unique for long-term vertical temperature trend analysis. However, due to different adjustments and analysis procedures used to calibrate shift of sensor temperature owing to on-orbit heating/cooling of satellite components and the inter-calibration of the different MSU instruments, large temperature trend differences were found among MSU data sets generated by different teams. Although surface temperatures based on in situ observations from 1979 to 2001 have warmed by ~ 0.13 K per decade, these significant uncertainties in UTLS temperature trends have resulted in a global warming controversy between surface and free troposphere and plagued efforts to quantify tropospheric and stratospheric temperature changes. Recently, the Global Positioning System (GPS) radio occultation (RO) limb sounding technique, which provides all-weather high vertical resolution refractivity profiles, has emerged as a robust global observing system. Because the basics of the GPS RO measurement is a time measurement against absolute timed and calibrated atomic clocks at the ground station, this data type is ideally for use as a climate benchmark data. In this study, we evaluate the temperature trend estimated by the microwave Lower Stratosphere Temperature (TLS) datasets from Remote Sensing System (RSS) and University of Alabama in Huntsville (UAH) with 51 months of Challenging Minisatellite Payload (CHAMP) Global Positioning System (GPS) radio occultation (RO) data. The value of GPS RO soundings for climate studies is demonstrated.