A global analysis of gravity wave activity in the upper troposphere and lower stratosphere region derived from GPS radio occultation data

T. SCHMIDT1, A. DE LA TORRE2, P. ALEXANDER2, C. ARRAS1, G. BEYERLE1, S. HEISE1, P. LLAMEDO2, J. WICKERT1, AND M. ROTHACHER1

Bologna, Italia

Congreso; SPARC; 2008

Global gravity wave (GW) potential energy distributions are retrieved from GPS radio occultation (RO) data from different satellite missions: CHAMP since 2001, GRACE and COSMIC since 2006. The RO technique uses GPS signals received aboard low orbiting satellites for atmospheric limb sounding. Atmospheric temperature profiles are derived with high vertical resolution. The GPS RO technique is sensitive to GWs with small ratios of vertical to horizontal wavelengths. The specific potential energy as a measure of GW activity is usually deduced from the temperature profile for each occultation event up to 35 km. To separate the GWs from the background a band-pass filter associated to different vertical wave lengths is applied to the measured temperature profiles. This GW analysis technique introduces significant artificial enhancement of wave activity at the tropopause, mainly in the tropics, depending on the ability of the band-pass filter to reproduce the tropopause kink. As an alternative to the usage of the temperature profile alone we discuss two additional methods for the derivation of the GW activity: (1) The GW analysis is considered for the troposphere and lower stratosphere separately by applying the band-pass filter up to the tropopause and from the tropopause to the end of the temperature profile. (2) Instead of the usage of temperature profiles we adopt potential temperature and refractivity profiles for the calculation of GW activity, taking into account the less abrupt course of this parameters in the vicinity of the tropopause region. The specific potential energy derived from the different methods will be discussed globally with respect to geographical regions/seasons and altitude intervals, whereas special attention is given to the tropical region.