A STUDY OF THE LOW-FREQUENCY INERTIO-GRAVITY WAVES OBSERVED DURING THE PYRENEES EXPERIMENT

The purpose of this paper is to analyze and interpret the onset of som e well-characterized transient inertio-gravity waves, observed during the PYREX (Pyrenees Experiment) campaign. The data used are the high-r esolution soundings, launched every 6 hours on both sides of the ridge . In agreement with other observations made during the field campaign, certain among those soundings often show steady mountain waves. It ap pears that those waves are often transients and are followed by well-c haracterized inertio-gravity waves, propagating upward and downward fr om the level where the initial mountain waves are large. To interpret those observations, it is suggested that the observed inertio gravity waves result from the geostrophic adjustment of the large-scale flow t hat follows the transit and eventually the breaking of the main mounta in wave. This hypothesis is supported by an analytical calculation of inertio-gravity waves emission from a momentum deposit that lasts a fi nite time. The spatial extent of this forcing are also finite, and its maximum amplitude is a fraction of the measured mountain drag.