Large Amplitude Gravity Waves above Southern Andes, Drake Passage and Antarctic Peninsula

Abstract

Previously to a research program to be accomplished during winter 2013 along Southern Andes Range and its prolongation in the Antarctic Peninsula (Southern Andes - ANtarctic GRavity wave InitiAtive (SAANGRIA)), large amplitude mountain and shear gravity waves observed with Weather Research and Forecasting (WRF) mesoscale model simulations during winter 2009 are analyzed. The simulations are forced with Era-Interim data. The approach selected for the regional downscaling is consecutive integrations with weekly reinitialization with 24 hours of spin-up and the outputs during this period are excluded from the analysis. From June 1 to August 31, 5 cases study were selected on the basis of their outstanding characteristics and large wave amplitudes. The complete period analyzed suggests that the 5 racetracks proposed for the SAANGRIA experiment are representative of the typical mountain wave morphology in the region. In general, one or two prevailing modes of oscillation are identi ed after applying continuous wavelet trans- forms at constant latitudes and pressure levels. In all cases, the prevailing modes are characterized by horizontal and vertical wavelengths around or shorter than 100 km and longer than 8 km respectively. Regional and syn- optic conditions for each case are described. The zonal and meridional components of the vertical ux of horizontal momentum is calculated for one of the cases, considering a broad wave spectrum and in particular the prevailing wave. A large relative contribution to this fux due to short horizontal wavelengths of the spectrum is observed in comparison with the momentum Donly transported by the prevailing mode, in agreement with theoretical results.