THE EFFECT OF DIFFERENT BACKGROUND SEPARATION METHODS ON GRAVITY WAVE PARAMETERS IN THE UPPER TROPOSPHERE AND LOWER STRATOSPHERE REGION DERIVED FROM GPS RADIO OCCULTATION DATA

SCHMIDT, T.; FABER, A.; DE LA TORRE, A.; LLAMEDO, P.; ALEXANDER, P.; HEISE, S.; WICKERT, J.

Congreso; COSPAR; 2012

When vertical temperature proles are used for the detection of gravity wave (GW) parameters a separation between a GW induced fluctuation and the background temperature field has to be performed. According the linear theory of GWs the measured temperature profile is expanded into a background temperature and a perturbation. The background is assumed to be steady, the fluctuations are much smaller than the background and the fluctuations should not affect the background. Usually, the fluctuations are addressed to GWs, but this depends strongly on the measuring method (observational filter) and the background separation approach. One possibility to separate GWs from the measurement is the application of band-pass filter associated to different vertical wavelengths to the measured temperature profiles. But, this analysis technique introduces an artificial enhancement of wave activity at the tropopause, mainly in the tropics, depending on the ability of the used filter to reproduce the tropopause kink. One possible method to solve this problem in the tropopause region is the separation of the profile into a tropospheric and a stratospheric part and the application of the filter for each region. A more appropriate approach is the double filtering method previously introduced. Alternatively tovertical detrending, a temperature background can be separated by horizontal detrending. For it temperature climatologies based on a suficient temporal and spatial data density and averaging intervals must be present. In this study we demonstrate and discuss global GW temperature variances, and vertical wavelengths and amplitudes retrieved from GPS radio occultation (RO) data from COSMIC (2009 and 2010) between 10 and 40 km based on the different vertical and horizontal detrending approaches. The RO technique uses GPS radio 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.