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

Abstract. The propagation of gravity waves (GW) 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 equations (HD) is used to derive the analytical dispersion equations and the GWs reflection coefficient. These equations are applied to the troposphere–stratosphere and stratosphere–mesosphere boundaries to analyze which part of the GWs spectra has the greatest chance of crossing them and affecting the dynamics of the upper atmosphere. We found that the GWreflection coefficient at the troposphere–stratosphere boundary increases significantly during SSW. This is not the case for the reflection coefficient at the stratosphere–mesosphere boundary 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 of the reflection coefficient. However, these additional GW fluxes are not sufficient to compensate for the reduction of GW fluxes coming from the troposphere to the mesosphere. As a result, there is mesospheric cooling accompanied by SSW events.