THE INFLUENCE OF HADLEY CIRCULATION INTENSITY CHANGES ON EXTRATROPICAL CLIMATE IN AN IDEALIZED MODEL

Experiments have been performed using a simple global model with ideal ized physics and zonally symmetrical forcings to investigate the influ ence of Hadley circulation intensity changes on extratropical climate. The heating within the Tropics is latitudinally concentrated, while t he heating in the extratropics is kept unchanged. This leads to an inc rease in the intensity of the Hadley circulation. As found earlier by Hou, along with the increase in the intensity of the Hadley circulatio n, there is a statistically significant temperature increase in the wi nter high latitudes. Zonal-mean diagnostics have been performed in ord er to identify the link between the changes in the Tropics and the ext ratropics. Detailed diagnosis of the heat budget shows that warming in the winter high latitudes is induced by changes in the mean meridiona l circulation, over the opposing cooling effects caused by changes in the eddy hear fluxes. Such a change is consistent with an equatorward shift of the jet stream and its associated heating pattern. It is sugg ested that the equatorward shift in jet position is caused by an incre ase in westerly acceleration within the Tropics associated with the en hancement in the intensity of the Hadley circulation. Limitations of t he model are also discussed.