Gravity waves as a mechanism of troposphere–stratosphere–mesosphere coupling during sudden stratospheric warming

Abstract

The propagation of gravity waves (GWs) and their role in the coupling of the troposphere–stratosphere–mesosphere atmospheric layers during sudden stratospheric warming (SSW) are studied. A standard set of hydrodynamic (HD) equations is used to derive the analytical dispersion equations and the GW reflection coefficient. These equations are applied to the troposphere–stratosphere and stratosphere–mesosphere discontinuities to analyse which part of the GW spectra has the greatest chance of crossing them and affecting the dynamics of the upper atmosphere. We found that the GW reflection coefficient at the troposphere–stratosphere discontinuity increases significantly during SSW. This is not the case for the reflection coefficient at the stratosphere–mesosphere discontinuity when the reflection coefficient decreases compared to its value in the no-SSW case. The generation of GWs in the stratosphere during the SSW is responsible for the reduction in the reflection coefficient. However, these additional GW fluxes are not sufficient to compensate for the reduction in GW fluxes from the troposphere to the mesosphere. As a result, mesospheric cooling accompanied by SSW events occurs.