THE VORTICITY BUDGET OF THE ZONE OF SUBTROPICAL HIGHS IN NORTHERN HEMISPHERE FOR WINTER

In this paper, the maintenance of the sub-tropical high in northern hemisphere for winter is discussed by means of the balance equation of the vorticity. The calculated results show that the divergence of the vorticity transfer due to the large-scale eddies is the dominant factor for maintainning anticyclonic vorticity in the region near 30°N. The anticyclonic vorticity due to this divergence process occurs mainly in the upper troposphere; at the same time, the transfer of earth rotation vorticity may effect the anticyclonic vorticity downward to the lower troposphere. The maintenance of the westerly jet is also discussed from the view-point of the vorticity transfer. The northward vorticity transfer by the large-scale eddies reaches its maximum value over 45°N, so that it may play an important role both for the maintenance of the mean zonal westerlies and its jet in the middle latitude. Over 30°N, however, the vorticity transfer by large scale eddies vanishes, and on the contrary, both the transfer of earth rotation vorticity and of the relative vorticity have larger value. Thus, it may be considered that the subtropical jet is maintained by the mean mcridional circulation.