Equatorward Propagation of Inertia–Gravity Waves due to Steady and Intermittent Wave Sources

Abstract

A simple ray-tracing model for the equatorward propagation of inertia–gravity waves in the lower stratosphere is investigated. The model is based on a zonally symmetric wave source and incorporates radiative wave damping. It is shown that steady extratropical wave sources are able to produce spectra of potential energy that exhibit a conspicuous peak at the equator, which resembles the spectral peaks that are often observed in field data. This reinforces the recent suggestion by other authors that such peaks are caused by the latitudinal variation of the local Coriolis parameter, though these authors did not consider horizontal wave propagation. Notably, horizontal wave propagation can produce equatorial peaks even with strictly extratropical wave sources. Wave source intermittency is then investigated by allowing for a time-dependent wave source. The source is treated statistically as a stationary random process and a number of general comments are made with respect to the impact of intermittenc... Abstract A simple ray-tracing model for the equatorward propagation of inertia–gravity waves in the lower stratosphere is investigated. The model is based on a zonally symmetric wave source and incorporates radiative wave damping. It is shown that steady extratropical wave sources are able to produce spectra of potential energy that exhibit a conspicuous peak at the equator, which resembles the spectral peaks that are often observed in field data. This reinforces the recent suggestion by other authors that such peaks are caused by the latitudinal variation of the local Coriolis parameter, though these authors did not consider horizontal wave propagation. Notably, horizontal wave propagation can produce equatorial peaks even with strictly extratropical wave sources. Wave source intermittency is then investigated by allowing for a time-dependent wave source. The source is treated statistically as a stationary random process and a number of general comments are made with respect to the impact of intermittenc...