Are we Observing Mountain Waves Above the Andes Range from GPS Occultation Profiles?

Abstract

GPS radio occultation temperature profiles retrieved from SAC-C and CHAMP exhibit a significant wave activity in the troposphere and lower stratosphere at midlatitudes (30°S to 40°S) above the Andes Range. Large amplitude structures, with long vertical wavelength, have been repeatedly reported in this region, as detected from other experimental devices and attributed to mountain waves. The possibility to associate the observed enhancements in wave activity to mountain forcing, or instead, to other significant sources in the region considered is discussed. The generation in the vicinity to a permanent jet situated above the mountains of inertio gravity waves by geostrophic adjustment, with longer horizontal and perhaps shorter vertical wavelengths than those expected from mountain waves, seems to be the main source. These waves could be more easily detected from GPS profiles than mountain waves. As it is known, inertio gravity waves are the means by which mass and momentum are redistributed so as to ultimately achieve geostrophic balance from an initially unbalanced state.