GPS Radio Occultation with CHAMP and SAC-C: Global and Seasonal Variations of Gravity Wave Activity

Gravity waves in the middle and upper atmosphere are believed to be excited mainly in the troposphere and lower stratosphere (TLS) and propagate upward, resulting in energy coupling between the lower and upper atmosphere. Therefore, it is of significant importance to study the basic features of gravity wave activities in the TLS. GPS satellites provide global atmospheric profiling with high vertical resolution (0.1-1 km) and high accuracy under all weather conditions. Recent satellites on board the German CHAMP (CHAllenging Minisatellite Payload) and the Argentine SAC-C (Satellite de Aplicaciones Cientificas-C) have allowed us to analyze gravity waves in the troposphere as well as in the stratosphere on near-global basis. The present study considers a data sample for 44 months that begins from May 2001 to December 2004 for CHAMP and 40 months from July 2001 to December 2004 for SAC-C occultation data sets. Seasonal and latitudinal variations of Potential energy (Ep) are evident at 20-30 km; in particular, Ep values are highly enhanced near the equator. Amplitudes of temperature fluctuations at 20-30 km could be somewhat reduced through the optimization of the occultation analysis. We have investigated variations of (T'/T)2 at 10-20 km and 20-30 km as a function of latitude and season.