A numerical simulation study of the major stratospheric warming and subsequent flow recovery during the winter of 1979

This is a study of the evolution of a stratospheric sudden warming throughout the onset, vortex breakdown, and recovery stages of the flow using an isentropic vertical coordinate model. Our goal is to gain insight into the dynamical processes at work in each of those stages.

The event selected developed during the winter of 1979. The model domain is the global middle-atmosphere above the 400-K surface, and the resolution is 5° longitude by 4° latitude and 23 layers spaced nearly evenly in height. The physical processes are represented by a Newtonian type heating/cooling. The initial conditions combine NCEP/NCAR reanalysis and NMC data. The Montgomery potential at the lower boundary is prescribed based on the observed data. More details on the model are presented in a companion paper.

The simulations produce a realistic evolution of the entire event. The onset stage is characterized by enhanced propagation of "wave activity" from the troposphere and the breakdown of the polar vortex into two cyclonic vortices. The mature stage shows the separation of these two vortices as three-dimensional structures develop in the flow. A narrow tongue of air with low potential vorticity extends from the tropics into the northern polar region. The recovery stage, which starts in the upper stratosphere, shows the re-establishment of a predominantly zonal flow. In this paper, we present a detailed three-dimensional analysis of the entire event.