Role of the Tibetan Plateau on the Annual Variation of Mean Atmospheric Circulation and Storm Track Activity

Abstract This study reexamines how the Tibetan Plateau (TP) modulates the annual variation of atmospheric circulation and storm track activity based on the Meteorological Research Institute?s atmosphere-ocean coupled model experiments with a progressive TP uplift from 0 to 100% of the present height. We have identified three major roles of the TP on atmospheric circulation and storm track activity. First, consistent with a previous finding, the TP tends to intensify upper-level jet and enhance baroclinicity in the North Pacific but significantly weaken storm track activity over the TP, East Asia, and the western North Pacific during the cold season. Second, the TP amplifies stationary waves that are closely linked to transient eddies. In particular, the TP enhances the Siberian high and the Aleutian low, which together contribute to the strengthening of the East Asian winter monsoon circulation and the weakening of storm track activity. Third, the TP significantly modulates the subseasonal variability of the Pacific storm track (PST) activity. In particular, the TP tends to suppress the PST activity during midwinter despite the fact that it strengthens baroclinicity along the Pacific jet. The midwinter suppression of the PST activity, which is well reproduced in a control run with a realistic TP, gradually disappears as the TP height decreases. Major factors for the midwinter suppression of the PST associated with the TP include (1) destructive effect of an excessively strong jet leading to an inefficiency of barotropic energy conversion, (2) reduction of baroclinicity over the northern part of the TP, and (3) subseasonally varying SST change and the resulting moist static energy.