A Study of Atmospheric Energetics During the January–February 1963 Stratospheric Warming

Abstract

The spectral energy equations for zonal and eddy kinetic and available potential energies are used to investigate the energetics of the lowest 30 km of the atmosphere during the months of January and February 1963. A major stratospheric warming, manifested in the reversal of the stratospheric meridional temperature gradient and destruction of the polar-night stratospheric vortex, began in mid-January. Data for eight standard pressure levels, from 850 to 10 mb, for every fifth day were utilized. The horizontal wind field was estimated by using both the geostrophic approximation and a modified stream function. The vertical motion field (dp/dt) was estimated both by the adiabatic technique and by the solution of the omega equation. The variation of the energy exchanges with height (pressure) indicates that the lower and middle troposphere and the middle stratosphere were baroclinically active regions before and during the warming. The principal path of energy flow in these regions was from zonal to eddy available potential energy, from there to eddy kinetic energy and thence to zonal kinetic energy. After the reversal of the meridional temperature gradient, however, the portion of the stratosphere studied rapidly lost eddy kinetic energy to other forms of energy. At all times eddy kinetic energy was supplied to the stratosphere by the upward flux of mechanical energy from the troposphere. The upper troposphere and lower stratosphere appear, as a whole, to contribute little to the net energy changes both before and after the warming. Barotropic effects are suggested, however, since the principal energy exchange in this region is from zonal to eddy kinetic energy. The upward flux of energy from the troposphere to the stratosphere is large compared with the energy exchange processes occurring in the stratosphere and must be considered a significant item in the budget of the stratosphere. A relationship between high-latitude blocking in the troposphere and the onset of the stratospheric warming is shown by comparing the variation of the 500-mb zonal wind with latitude and time with the average absolute vertical motion (dp/dt) for a mid-tropospheric and a mid-stratospheric level. Increased vigor of the vertical motion field accompanies both the onset of blocking in the troposphere and the warming in the stratosphere. Some speculation is offered concerning the interpretation of this relationship as it pertains to the cause of the stratospheric warmings.