Generation of inertia-gravity waves by the midlatitude tropospheric jet is studied on the basis of the data obtained from the radiosoundings over the North Atlantic during the FASTEX campaign. A sample of 224 radiosoundings is used to analyze the wave activity as a function of the distance to the jet. It is shown that radiosoundings displaying the most intense gravity-wave activity, both in the stratosphere and in the troposphere, are the ones closest to the jet. Thus, the jet region is the dominant source of gravity waves in this region far from the orography. Further examination allows for identification of two specific regions of the flow that are associated with intense gravity wave activity: the vicinity of the maximum of the jet velocity, and the regions of strong curvature of the jet.

By detailed case studies we then show that geostrophic adjustment is the dynamical mechanism responsible for the generation of large amplitude inertia-gravity waves in the regions of the strong curvature of the wind. The generation of waves in the vicinity of the region where the wind veers, in the deep troughs of the geopotential, appears to be systematic.