Internal gravity wave emission into the middle atmosphere from a model tropospheric jet

Abstract

A mechanism is investigated whereby large amplitude internal gravity waves (IGWs) may be excited by the tropospheric jet stream when this is driven to parallel shear instability following a rapid external forcing of the mean flow, a circumstance that might be realized, for example, through ageostrophic effects in the process of baroclinic wave development. A series of mean states are examined, first on the basis of linear theory, to determine the characteristics of the most unstable normal mode, which is expected to dominate the initial stages of flow evolution. On the basis of linear theory, the authors show that it is possible to assess whether IGWs will be strongly excited by examining whether the initial instability satisfies an easily calculable criterion that has been previously termed the "penetration condition'. -from Authors