Generation of normal atmospheric modes by stratospheric vacillations

Abstract

A number of numerical experiments were performed with the use of the middle and upper atmosphere model (MUAM). In these experiments, the atmospheric response to an external excitation in the troposphere was calculated and internal stratospheric vacillations caused by the interaction of stationary planetary waves (SPWs) with the zonal mean flow were modeled. The MUAM is shown to well reproduce the known high-frequency global resonance responses of the atmosphere to an external excitation. The results of modeling show that the stratospheric vacillations caused by the interaction of SPWs and the mean flow are responsible for the generation of low-frequency normal modes in the lower and middle atmosphere. The activity of normal atmospheric modes in the troposphere and stratosphere is noted to increase simultaneously with the development of sudden stratospheric warmings. However, in order to understand which process is primary, an additional analysis of the results of numerical experiments and stratospheric data is necessary. It is inferred that, for an adequate modeling of stratospheric vacillation cycles, atmospheric general circulation models must be capable of reproducing global resonance properties of the atmosphere.