A composite analysis of the stratospheric sudden warmings simulated in a perpetual January integration of the Berlin TSM GCM

A 7,200-day dataset from a perpetual January integration of the Berlin Trop osphere-Stratosphere-Mesosphere General Circulation Model is analyzed to cl arify the basic nature of the dynamical linkage between the stratosphere an d the troposphere. Much attention is paid to the stratospheric sudden warmi ng events; sixty-four events are detected in this dataset, with no clear pe riodicity. The 64 sudden warming events are divided into two groups according to the r elative strength of planetary waves of zonal wavenumber 1 and 2 in the stra tosphere, although each event has its own dynamical characteristics. Compos ites for each group show some general features of the stratospheric sudden warmings, including the "preconditioned" zonal mean states in the lower str atosphere and the upward propagation of the enhancement of planetary-scale waves from the troposphere to the stratosphere. In the preconditioned state s the zonal mean temperature is lower than normal in the polar region, and the zonal mean zonal wind is stronger in the middle and high latitudes. Each group shows some different dynamical behavior, not only in the stratos phere but also in the troposphere before, during and after the sudden warmi ng events. In the group in which the wavenumber I component dominates, the preconditioned states are more evident and confined to lower altitudes. Suc h states continue even after sudden warming events near the tropopause. In the other group of wavenumber 2 dominance, signals of sudden warming descen d to the upper troposphere after the events.