Isla Simpson
Atmospheric Physics Department, University of Toronto
"The role of eddies in driving the tropospheric response to stratospheric heating perturbations"
In recent years it has become apparent that changes in the stratosphere could have an impact on tropospheric circulation. However, the exact mechanisms involved in coupling between the stratosphere and troposphere remain uncertain. Understanding these mechanisms is potentially important for many climate forcings such as the 11-year solar cycle, ozone depletion/recovery and increasing greenhouse gas concentrations.
Previous studies using simplified general circulation models (GCMs) have suggested that heating or cooling of the lower stratosphere can result in latitudinal displacements of the tropospheric mid-latitude jets and storm-tracks. The direction of displacement has been found to be dependent on the distribution and localisation of the stratospheric change in a manner consistent with the observed tropospheric response to various forcings such as solar variability and ozone depletion.
Here, a simplified GCM is used to investigate the mechanisms involved in producing the tropospheric response to heating or cooling of the lower stratosphere. The key mechanism is shown to involve feedbacks between eddy momentum fluxes associated with tropospheric transient eddies and the wave-refraction characteristics of the large scale flow. The altered vertical temperature gradient at the tropopause and its latitudinal extent determines the direction of displacement of the tropospheric jet; wave-induced accelerations in the troposphere produce a positive feedback on the source and propagation of baroclinic waves. These dynamical processes are closely related to those giving rise to natural annular variability in the simplified GCM.
Host: Prof. Lorenzo Polvani
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