A study of the stratospheric major warming and subsequent flow recovery during the winter of 1979 with an isentropic vertical coordinate model

The principal goal of this paper is to gain further insight into the dynami cal processes during the stratospheric major warming of February and early March 1979, with a special emphasis on the recovery stage. To achieve this goal, first the entire evolution of the warming event is numerically simula ted using an isentropic vertical coordinate model. Then the results from th e following complementary points of view are quantitatively analyzed: wave effects on the mean flow, potential enstrophy conversion and transport, and potential vorticity redistribution on a synoptic chart. There is an indication that wavenumber 1 during the recovery stage amplifie s through a mechanism within the stratosphere and propagates downward. The simulated Eliassen-Palm flux field shows that the amplified wave 1 is respo nsible for the mean flow acceleration in the recovery stage. It is therefor e concluded that the in situ amplification mechanism for wave 1 plays a cru cial role in the dynamics of the flow recovery. In order to examine the mec hanism, detailed analyses of the simulated eddy potential enstrophy budget are performed. It is found that there is an "anticascade'' of potential ens trophy in the recovery stage through which wave 1 amplifies in the midstrat osphere. This result is consistent with a synoptic description of the event in terms of potential vorticity distribution on isentropic surfaces.