Momentum flux generated by large amplitude gravity waves above Southern Andes and the Antarctic Peninsula analyzed through mesoscale simulations

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

Congreso; SPARC; 2012

The role of gravity waves (GW) in forcing the global-scale circulation and the thermal structure of the lower and middle atmosphere has long been recognized. Diverse GW drag parameterizations of general circulation models significantly differ in the way they simulate the GW momentum-flux deposition into the mean flow, so they induce different large-scale behaviors. There is therefore a need to understand GW momentum flux generation above significant sources in higher resolution simulations. We analyze large-amplitude gravity waves generated above Andes in the South of the Patagonia region and the prolongation of the mountain range in the Antarctic Peninsula during the winter of 2009. This zone has been observed in various satellite data sets to exhibit in winter among the largest GW amplitudes and momentum fluxes at stratospheric altitudes of any region on Earth. We use Weather Research and Forecasting (WRF) mesoscale model simulations, which are forced with 0.5o x 0.5o ERA-Interim data from the European Centre for Medium-Range Weather Forecasts (ECMWF). Several case studies were selected on the basis of their outstanding characteristics. The calculated zonal and meridional components of the vertical flux of horizontal momentum are shown. The flux decreases with increasing height after a progressive deposition of momentum by different possible mechanisms. A prevailing negative zonal component is observed. A comparison with previous experimental results in this region is performed. Partial wave reflection near the tropopause is suggested by considerable departures from equipartition between potential and kinetic wave energy. This work is a follow up of the previous presentation by de la Torre et al.