Large-amplitude gravity waves above the southern Andes and the Antarctic Peninsula

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

Congreso; SPARC; 2012

Above the southern Andes range and its prolongation in the Antarctic Peninsula, large-amplitude mountain and shear gravity waves observed with Weather Research and Forecasting (WRF) mesoscale model simulations during winter 2009 are analyzed. This study was motivated by a decade of satellite observations of temperature fluctuations in the stratosphere, allowing us to infer that this region may be launching the largest-amplitude gravity waves into the middle and upper atmosphere. The simulations are forced with ERA-Interim data from the European Centre for Medium-Range Weather Forecasts. From 1 June to 31 August 2009, five case studies were selected on the basis of their outstanding characteristics and large wave amplitudes. In general, one or two prevailing modes of oscillation are identified after applying continuous wavelet transforms at constant pressure levels and perpendicularly to the nominal orientation of the dominant wave crests. In all cases, the dominant modes are characterized by horizontal wavelengths around 50 km. Their vertical wavelengths, depending on a usually strong background wind shear, are estimated to be between 2 and 11 km. The corresponding intrinsic periods range between 10 and 140 min. In general, the estimated vertical wavelength (intrinsic period) maximizes (minimizes) around 250–300 hPa. The synoptic circulation for each case is described. A comparison with previous experimental results reported in the region from in situ and remote sensing measurements is performed.