On the Dynamics of the Wintertime Stratosphere Circulation

Abstract

The dynamics of the large-scale circulation pattern of the stratosphere in mid-winter is examined. A set of energy equations is derived which is applicable to the stratosphere as an open system. The terms of these equations, interpreted as energy conversions and fluxes, are evaluated using data from January 1958. The computed energy conversions were similar in sign to those found in the troposphere, and varied only in magnitude during the month, reaching maximum values prior to and during the stratosphere warming. The energy flux terms indicate a considerable amount of energy was transferred into the stratosphere through a correlation of the vertical velocity and geopotential, at the expense of energy of the troposphere. The possibility of a stratosphere-troposphere coupling is investigated further through harmonic analyses of the height field at levels from 1000 mb to 10 mb at 50N. A vertical consistency of the long waves is revealed, throughout the depth studied, and evidence is found for the existence of periodic amplifications of wave numbers one and two which propagate upwards at the rate of about 6 km per day. From observational evidence a model is deduced to explain many of the observed features of the stratosphere circulation.