The Influence of Hadley Circulation Intensity Changes on Extratropical Climate in an Idealized Model

Abstract

Experiments have been performed using a simple global model with idealized physics and zonally symmertrical forcings to investigate the influence of Hadley circulation intensity changes on extratropical climate. The heating within the Tropics is latitudinally concentrated, while the heating in the extratropics is kept unchanged. This loads to an increase in the intensity of the Hadley circulation. As found earlier by Hou, along with the increase in the intensity of the Hadley circulation, there is a statistically significant temperature increase in the winter high latitudes. Zonal-mean diagnostics have been performed in order to identify the link between the changes in the Tropics and the extratropics. Detailed diagnosis of the heat budget shows that warming in the winter high latitudes is induced by changes in the mean meridional circulation, over the opposing cooling effects caused by changes in the eddy heat fluxes. Such a change is consistent with an equatorward shift of the jet stream and its associated heated pattern. It is suggested that the equatorward shift in jet position is caused by an increase in westerly acceleration within the Tropics associated with the enhancement in the intensity of the Hadley circulation. Limitations of the model are also discussed.