Heat balance and mean meridional circulations in the polar stratosphere during the sudden warming of January 1958

Abstract

In order to gain a greater understanding of the physical processes acting in the lower stratosphere during a major breakdown of the polar night vortex, a computation of the direction and magnitude of the mean meridional circulation is performed by employing a heat budget method. This computation reveals that the mean cell operates to produce rising motion over the polar regions before, during, and after the breakdown period. The calculations show that horizontal eddy heat flux provides the predominant mechanism for the large temperature increases observed over the polar cap during the time of the vortex breakdown. As a supplement to thea bove computation, mean vertical velocities were determined with respect to a curvilinear coordinate system oriented along a line of maximum circulation intensity at 50 mb. The result showed that the mean cell operates in the direct sense prior to the major breakdown when measured relative to this curvilinear system.