| Čoahkkáigeassu: | Tropospheric heating perturbations and topography are used to create Northern Hemisphere winter-like stratospheric variability in an idealized atmospheric general circulation model. Wave 1 and wave 2 heating perturbations as well as wave 2 topography are used. With appropriate choices of amplitudes, the three forcings produce reasonable sudden stratospheric warming (SSW) frequencies. It is found that large numbers of both split and displacement sudden warmings occur when the model is forced by heating perturbations, regardless of the wave number of the forcing. This is different from the wave 2 topographic forcing, which produces almost only splits. We use the results of the three model runs to investigate the extent to which SSWs are caused by anomalous tropospheric wave fluxes. We find that SSWs in this model can form both as a direct result of anomalous tropospheric wave activity and due to internal stratospheric processes which alter the propagation of tropospheric wave flux into the stratosphere and that the fraction of the two mechanisms is similar to that of the observed atmosphere for all three forcings. We further investigate the circulation differences associated with splits and displacements and find that splits and displacements have different zonal mean surface signatures when the model is forced by wave 1 heating.
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