The investigation addresses the interaction between extratropical wave activity and the mean meridional circulation. A simplified troposphere- stratosphere GCM is employed to estimate the impact of orography and prescribed local heat sources on the residual circulation in the northern winter troposphere and stratosphere.
It is found that only the combined action of orographic and midlatitude thermal forcing of stationary waves induces a residual circulation typical for the northern winter hemisphere, with the stratospheric branch ranging continuously from tropical to polar latitudes. Intensifications of the stratospheric residual circulation are generally associated with, firstly, a reduced polar night jet accompanied by enhanced easterlies in low and summer hemispheric latitudes and, secondly, substantial warming in high latitudes completely compensated by cooling in the tropics and subtropics. These results fit qualitatively well to the observed asymmetry between the northern and southern winter hemispheric stratosphere.
The idealizations ensure that diabatic heating in the deep tropics is almost identical for all model configurations. Therefore, enhanced upwelling in the tropical lower stratosphere is remotely determined by stronger wave activity in the extratropical stratosphere and thus induced by modified forcing of stationary waves in the extratropical lower troposphere. This connection provides further evidence for the concept of the extratropical wave pump.
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12th Conference on Atmospheric and Oceanic Fluid Dynamics