A Composite Analysis of the Stratospheric Sudden Warmings Simulated in a Perpetual January Integration of the Berlin TSM GCM

Abstract

A 7, 200-day dataset from a perpetual January integration of the Berlin Troposphere-Stratosphere-Mesosphere General Circulation Model is analyzed to clarify the basic nature of the dynamical linkage between the stratosphere and the troposphere. Much attention is paid to the stratospheric sudden warming events; sixty-four events are detected in this dataset, with no clear periodicity.
The 64 sudden warming events are divided into two groups according to the relative strength of planetary waves of zonal wavenumber 1 and 2 in the stratosphere, although each event has its own dynamical characteristics. Composites for each group show some general features of the stratospheric sudden warmings, including the “preconditioned” zonal mean states in the lower stratosphere and the upward propagation of the enhancement of planetary-scale waves from the troposphere to the stratosphere. In the preconditioned states 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 stratosphere but also in the troposphere before, during and after the sudden warming events. In the group in which the wavenumber 1 component dominates, the preconditioned states are more evident and confined to lower altitudes. Such states continue even after sudden warming events near the tropopause. In the other group of wavenumber 2 dominance, signals of sudden warming descend to the upper troposphere after the events.