ON THE EXISTENCE AND STRENGTH OF THE SUMMER SUBTROPICAL ANTICYCLONES - BERNHARD-HAURWITZ-MEMORIAL-LECTURE

The subtropical anticyclones are usually related to radiative cooling and the descending arm of the Hadley Cell. This explanation works well for the winter anticyclone belt. However, the summer subtropical anti cyclones are in most measures stronger, as well as being more longitud inally localized, than their winter counterparts. The nature of the ci rculations in the summer and winter subtropics, and the Tropics are co mpared. It is hypothesized that the basic cause of the summer anticycl ones is the monsoonal latent heat release over the neighboring contine nts to the east. As this diabatic heating pushes poleward to near 25 d egrees latitude, so deep descent is induced poleward and westward of i t. Orographic effects can act to localize this descent. Enhanced radia tive cooling and suppressed convection are then viewed as amplifiers o f the descent. Under this descent is the equatorward moving air of an anticyclone, which is centered to the west. This wind acts to drive oc eanic upwelling, leading to cold sea surface temperatures and reinforc ement of the suppression of convection.