Interannual variation and hemispheric asymmetry of convectively-generated gravity waves as observed by MLS and AMSU

Gravity waves (GWs) from tropical deep convection in the troposphere are important sources for wave drags in the mesosphere. After the background wind filtering in the upper troposphere and lower stratosphere, the survived waves are mostly of long (7-20km) vertical and short (100-300km) horizontal wavelengths, which can be measured by satellite microwave radiometers like MLS (Microwave Limb Sounder) and AMSU (Advanced Microwave Sounding Unit). In this paper, we present multi-year climatologies of GW variances deduced from MLS (1992-1994) and AMSU-A (1998-2003) radiances at several altitudes between 28-80km. The three-year MLS observations at 28 and 33 km reveal a clear QBO (Quasi Biannual Oscillation) influence on GW propagation in the lower stratosphere. In the upper stratosphere and lower mesosphere, GW variances seen by MLS and AMSU are correlated well to the strength of the summertime subtropical jet at these heights. Although the longitudinal distribution of GW variances resembles very much tropical deep convection climatology, the centers of GW variances shift slightly poleward in latitude and eastward in longitude. As the center of the jet moves poleward with height, so does that of GW variances. In the upper stratosphere, MLS and AMSU GW climatologies differ in the variance ratio between northern and southern summers. Unlike MLS observations, AMSU results show significant weaker GW variances for the boreal summers than for the austral summers. These GW properties and differences will be further investigated as new satellite (such as Aura MLS) data become available.