Planetary Wave Activity in the Troposphere and Stratosphere during the Northern Hemisphere Winter

Abstract

This paper describes the correspondence of planetary wave activity between the troposphere and the stratosphere during the Northern Hemisphere winter from December 1981 to March 1982 using Elliassen?Palm E;P) flux diagnostics. Two typical cases of correspondence are found during this period. In December and early January (period 1), the time variation of wave activity in the troposphere and stratosphere is out of phase; when the tropospheric wave activity is, vigorous the stratospheric wave activity is quiet, and vice versa. In February and March (period 2), after the stratospheric sudden warming, the tropospheric wave activity seems to propagate into the stratosphere. These two periods (period 1 and 2) are characterized by the following dynamical features. The mean zonal geostrophic wind at middle latitudes in the upper stratosphere is stronger in period 1 than in period 2. The meridional gradient of the mean zonal wind velocity at high latitudes in the troposphere and lower stratosphere is steeper in period 2 than in period 2. Consequently, significant changes in the refractive index are observed between the two periods. The, E-P flux vectors in the troposphere and lower stratosphere regularly point upward in period 2, while they branch off equatorward and poleward around the tropopause level in period 1. This feature of the E-P flux pattern is in broad agreement with the refractive index. It is also observed that there exists a strong convergence zone of the E-P flux in the upper troposphere and dust the intensity of the convergence varies with a time scale of 10?15 days. This variation is closely related to that of the wave activity in the troposphere and stratosphere. Finally, it is briefly shown that some of these features for the Northern Hemisphere can be observed in the Southern Hemisphere also.