A Study About The Characteristics Of The Airflow Of The South Of Tibetan Plateau And Its Influence On The General Circulation Around It

Utilizing the NECP/NCAR reanalysis data and the GPCP data, the annual atmospheric circulation over East Asia from 1981 to 2000 is investigated. Based on it, the Characteristics of the airflow over the south of Tibet Plateau (including the Tibetan Plateau topographic trough and the perennial south wind over the southeast of Tibetan Plateau) is investigated. Further more, it is researched the relationship between the airflow over the south of Tibet Plateau and the circulation around it. The main results are as follow:(1) It is discovered that a zonal positive vorticity belt maintains to the south of Tibetan Plateau, due to the interaction of the plateau boundary layer and its neighboring free atmosphere. Particularly, there is an obvious topographic trough related to the positive vorticity near 90°E. In light of this, a Tibetan Plateau South Topographic Trough Index (TPSTTI) is defined in the paper over the key areas (80-90°E, 25°N). The index is proved to be effective in distinguishing between the characteristic of the Tibetan Plateau South Topographic Trough (TPSTT) and that of the Bay of Bengal Trough (BBT). The annual variation of the TPTT is strong in summer and weak in winter, and it shows significant abrupt changes during April, June and October.(2) The Tibetan plateau heating effect is the important factor of the annual variation of the TPSTT. The latter's abrupt changes are primarily induced by the seasonal sudden jump of the former. In winter, the low-level anticyclone caused by the Tibetan plateau cooling is strengthened and superimposes the westerly wind that should have been strengthened by dynamic effect, which weakens the TPTT. However, from spring to summer, the low-level cyclone resulting from the Tibetan plateau heating strengthens the circumferential westerly and deepens the TPTT.(3) The interaction between the TPSTT and the Sir Lanka cyclone is the pushing mechanism of Asian summer monsoon, especially for the South China Sea summer monsoon.. The TPTT propagates southward and the vortex near Sir Lanka moves northward continuously, till they meet and interact over the Bay of Bengal. This is the direct process of the subtropical high belt splitting initially over Bay of Bengal and the establishment of the BOBT. Subsequently, the southwesterly wind becomes stronger and promotes the eastward retreat of subtropical high, causing the South China Sea summer monsoon bursts over the whole South China Sea.(4) It is discovered that a key area which is blow south wind all the year is on the southeast of the Tibet Plateau. Its occurred is because the airflow over the Tibet Plateau. The south wind can reach the 600hPa, which is grows very high. The south wind is strong in summer and weak in winter, showing a double peak. A peak occurs in 15^th pentad and the other peak occurs in 36^th pentad.(5) The occurring reason of the two peaks of the south wind is different. The south wind peak occurred in 15 is because a low-level cyclone which caused by Tibetan plateau heating cover over the south wind. It causes the south wind stronger, and then south China comes into rainy period. The south wind peak occurred in 365^th is because the South China Sea monsoon onset, the south wind before the Bay of Bengal Trough cause the south wind become stronger. And then it is bring the rain over Yangtze River.(6) There is a good relationship between the south wind on the southeast of Tibetan Plateau and Chinese rainy. In 14^th pentad, the south wind on the southeast of Tibetan Plateau becomes stronger and expands eastwardly, and then the rainy in the south of China becomes heavy. In 35^th pentad, the south wind on the southeast of Tibetan Plateau gets much stronger with the Chinese rainy belt move to the Yangtze River.