The Interaction Between Atmospheric Circulation On Tibetan Plateau And Cyclonic Storm Activities Over The Bay Of Bengal

The cyclonic storms over the Bay of Bengal and atmospheric circulation on the Tibetan Plateau both have great impact on weather and climate in our country. But the interaction between systems over the two adjacent areas has not been well understood. In this study, the relationship between storm activities over the Bay of Bengal and heat resource over East Asia region was first explored though correlation analysis. Then, the characteristics of atmospheric circulation on anomaly heat resource years over Tibetan Plateau were composited to explore its influence on the cyclone activity. On the other hand, Atmospheric circulation features over Tibetan Plateau during early summer with cyclonic storm activities over the Bay of Bengal were investigated and cases of consistent snowfall and heavy rainfall over Tibetan Plateau under influence of cyclonic storms are selected respectively to learn the impact mechanism. Finally, numerical simulation and sensitivity experiments were designed to learn the impact of storms over the Bay of Bengal on heavy rainfall event over Southeast Tibetan Plateau. The main conclusions are summarized as follows.Correlation analysis shows that there is some correlation between the activities of storms over Bay of Bengal and heat source over the southeast of the Tibetan Plateau. Number of storms is negatively(positively) correlated with heating anomaly in the eastern Tibetan Plateau during early summer(autumn). Comparison study indicates when the heat source in the Tibetan Plateau enhance(weaken) in early summer, the South Asian anticyclone locates more northwardly(southwardly) and convections over Bay of Bengal decrease(increase). However, during autumn, when the heat source strengthens, the South Asian High over Bay of Bengal extends with the enhanced divergence in upper level atmosphere, which increases the low-level ascending flow and decreases the vertical wind shear. While when the heat source is not strong, the vertical wind shear could be larger and the convections over Bay of Bengal lose their activities.In turn, the storm activities over the Bay of Bengal also have great impacts on the circulation over the Tibetan Plateau. Composite analysis shows that during the period with storm activities, as the South Asia High moves northwardly, the south branch trough deepens and convective systems such as shear line become active. Meanwhile, the heat source and moisten sink in southeast of Tibetan Plateau are enhanced and the ascending motions strengthen significantly, which is benefit to the rainfall over Tibetan Plateau. It is found that the storms transport warm and wet air to the south of Tibetan Plateau via southerly low-level jet, providing energy and moisture for the rainfall. Besides, the dynamic forcing of Tibetan Plateau terrain also plays important role in the heavy rainfall.