Recent results on GW activity and propagation in Southern Andes and Antarctic Peninsula UTLS with GPS radio occultations

A. DE LA TORRE, P. ALEXANDER, P. LLAMEDO, R. HIERRO, A. ROLLA, T. SCHMIDT, J. WICKERT

Foz de Iguazu

Congreso; AGU 2010; 2010

American Geophysical Union

The global distribution, generation and variability of horizontal and vertical gravity waves (GWs) propagation, their energy content and the vertical flux of horizontal momentum are basic ingredients in the understanding of the lower and middle atmosphere dynamics. The Global Positioning System (GPS) Radio Occultation (RO) technique has global coverage and is capable of generating high vertical resolution temperature (T) profiles of the troposphere and stratosphere with sub-Kelvin accuracy and long-term stability, regardless of weather conditions. The UTLS region above the southern Andes Range, Drake Passage and Antarctic Peninsula constitute a natural laboratory where the effect of orographic and non-orographic GW sources compete between them in the total balance of wave energy. In this talk, we discuss recent results focused to this region. We first describe a long-term seasonal and geographical GW amplitudes, vertical wavelengths and activity from the CHAllenging Minisatellite Payload (CHAMP) GPS RO T data. The observed features complement observations in the same zone by other satellite passive remote sensing instruments, which are able to detect different height regions and other spectral intervals of the wave spectrum. A significant seasonal variation of wave activity is observed. Topography is an important source and some strong wave activity is also found over open ocean. Critical level filtering is shown to have an attenuation effect, implying that a large fraction of the observed activity can be considered to be an outcome of mountain waves. The wave fronts, nearly aligned with the North-South direction, are easily detected by the nearly meridional line of sight characterizing most of the GPS RO observations. Then we adapt a previous method for the determination of horizontal propagation of large amplitude GWs by Ern et al (2004), intending to optimize the available information from the highly inhomogeneous geographic distribution of GPS RO soundings. To remove the remaining -phase uncertainty in the horizontal wave propagation vectors we apply physical arguments. The geographic distribution of estimated uncertainties in the determination of mean specific potential energy is discussed. Finally, taking advantage of the anomalously high density of occultation events during the initial mission months of COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate) we choose two pairs of GPS RO, both containing occultations that occurred close in time and space. One pair shows a significant difference between both T profiles. Numerical simulations with a mesoscale model were performed in order to understand this discrepancy, which may be attributed to the presence of a non-isotropic structure.