Normal Mode Rossby Waves Observed in the Upper Stratosphere. Part II: Second Antisymmetric and Symmetric Modes of Zonal Wavenumbers 1 and 2

Abstract

As an extension of our recent previous study, the global structure and behavior of higher-mode Rossby waves am investigated with the aid of TIROS-N and NOAA-A satellite observations for the period November 1979 through April 1982. It is shown that the second antisymmetric and symmetric modes of zonal wavenumbers 1 and 2 exist in the upper stratosphere, although the existence of zonal wavenumber 2 modes somewhat uncertain. These waves are amplified in the winter hemisphere over a period of 1-2 months. The vertical structure of the waves is similar to that of the simple Lamb mode except for a little westward phase tilt. The period band of the higher-degree modes is variable, as predicted by numerical models. The period band of the second antisymmetric mode of zonal wavenumber 1, i.e.,(1, 2) mode, sometimes falls into that of a 16-day wave which is the manifestation of the (1, 3) mode. However, the two modes don't coexist in the same period band. The higher-degree modes are often largely amplified simultaneously. In particular, it is remarkable that they are enhanced before the occurrence of stratospheric sudden warmings. Since the amplitude of these waves is of the same order of magnitude as that of stationary waves, the interference between the traveling and stationary waves may play an important role in the sudden warming event.