Atmospheric Vacillations in a General Circulation Model. II: Tropospheric-Stratospheric Coupling and Stratospheric Variability

Abstract

Abstract The transient behavior of the stratosphere and its relationship to fluctuations in the dynamical coupling between troposphere and stratosphere has been investigated. The analysis is based on a 124-day sequence of atmospheric statistics generated in an 18-level hemispheric general circulation model set up for annual mean conditions. The model results are assumed to be representative of the winter half-year because of a bias in the model toward winter conditions. Examination of the various forcing terms demonstrates that the dynamical coupling is dominated by the w′ϕ′ flux. This flux maximizes at subpolar latitudes and experiences a quasi-periodic fluctuation which is controlled by the tropospheric vacillation cycle, thus indicating a plausible connection between this vacillation cycle and stratospheric warnings. Both long- and short-term stratosphere variations are largely controlled by the fluctuations of the w′ϕ′ flux. The convergence of this flux is shown to force corresponding variations in th...