Energetics of a "Minor Breakdown" of the Stratospheric Polar Night Vortex

Abstract

An investigation of the kinetic energy budget of a "minor breakdown" of the stratospheric polar night vortex is performed. The computation covers the period 15 November-15 December 1958, for the 100-50 mb layer north of 40N. Vertical motions and mean meridional circulations are computed from the thermodynamic equation. The calculations show a two-cell pattern with descending motions in mid-latitudes and ascent over the polar cap. During the period of restabilization after the "minor breakdown," a small area of mean descent appears over the polar cap. During the amplification stage, the internal energy conversions are acting to increase the eddy kinetic energy. The mean meridional circulation is direct at higher latitudes, opposite to that occurring during a major breakdown. The restabilization period is characterized by a reversal in sign of the internal energy conversions and by large boundary fluxes of zonal kinetic energy. Kinetic energy dissipation values are obtained as computational residuals. The valu~ are large and probably unrealistic. It is shown that spuriously large computed kinetic energy dissipations can result from errors in the radiational estimates.