Global and Seasonal Variations of Stratospheric Gravity Wave Activity Deduced from the CHAMP/GPS Satellite

Abstract

Global analyses of gravity wave (GW) activity in the stratosphere are presented using radio occultation data from the Challenging Minisatellite Payload (CHAMP) satellite. Temperature profiles obtained from CHAMP/ GPS radio occultations are first compared with ground-based instruments. In general, good agreement is found between these different techniques. Monthly mean values of potential energy Ep, being a measure of GW activity, which is estimated with radiosonde observations, are compared with CHAMP/GPS data and it is found that radiosonde-observed Ep values are slightly higher than those estimated with radio occultations. Strong diurnal variation of GW activity has been found. From the global morphology of GW activity, large Ep values are noticed, besides at tropical latitudes, even at midlatitudes during winter, but not during equinoxes. This suggests that wave activity at stratospheric heights is not only modulated due to orography (mountain/lee waves) but mainly depends on seasonal variations at the respective latitudes. Significant correlations are found between GW activity and the outgoing longwave radiation (OLR) observations, OLR being a proxy for tropical deep convection. Gravity wave activity is found to be high in the zones of deep convection confirming that convection is the major source of GW generation in the Tropics. Latitudinal and vertical variations of GW activity reveal the existence of large Ep values below 25 km and low values between 25 and 30 km in all the seasons near the equator. During the Southern Hemisphere winter, large values are noticed. Large values are also found during equinoxes, and these values are nearly the same in Northern and Southern Hemispheres (NH and SH, respectively) at midlatitudes. During solstices, the Ep distribution involves a larger hemispheric asymmetry at middle and higher latitudes. The latitudinal range is wide (±30° latitude in both hemispheres) with large Ep values in all seasons. Large values of Ep are noticed during the major stratospheric sudden warming that occurred over Antarctica during September 2002.