Seasonal variation of gravity wave activity at midlatitudes from 7 years of COSMIC GPS and Rayleigh lidar temperature observations

Abstract : 7-year series of gravity wave (GW) potential energy at mid-latitude stratosphere (10 .. 50 km) is constructed by combining temperature profiles provided by COSMIC GPS satellite constellation and Rayleigh lidar operating at Haute Provence observatory in Southern France. The combined series are used to evaluate the representation of GW in MERRA reanalysis. The seasonal and zonal variabilities of GW activity are diagnosed using zonal wind and wind divergence provided by ERA-Interim reanalysis. The spatiotemporal distribution of GW activity is found strongly dependent on the zonal wind variation, wind divergence and topography. We show that anomalies in the wind divergence can serve as a proxy for locating synoptic-scale enhancements of GW. The analysis provides evidence for orographic GW excitation and the results are compatible with geostrophic adjustement being an additional source of stratospheric GW. The seasonal GW variability can be largely explained by interaction with the mean flow and wave propagation.