青藏高原的热力和机械强迫作用以及亚洲季风的爆发*I.爆发地点

Thermal and Mechanical Forcing of the Tibetan Plateau and the Asian Monsoon Onset. Part I: Situating of the Onset

使用欧洲中期天气预报中心（ＥＣＭＷＦ）的客观分析资料、ＥＣＭＷＦ／ＴＯＧＡ补充数据集，美国ＮＭＣ气候分析中心的向外长波辐射（ＯＬＲ）资料以及国家气候中心存档的中国３３６个测站的降水资料，研究了１９８９年春天青藏高原和邻近地区的热力特征和环流特征，及其对亚洲季风区季节转换的影响。文中集中分析了表面感热和潜热通量的时空分布特征。结果表明：１９８９年亚洲季风的爆发由三个接续的阶段组成。第一阶段是５月上旬在孟加拉湾东岸，称为孟加拉（ＢＯＢ）季风爆发阶段。第二阶段是５月２０日左右开始的中国南海（ＳＣＳ）季风爆发阶段。第三阶段是６月１０日左右开始的印度上空的南亚季风（或称印度季风）的爆发阶段。分析表明，正是由于青藏高原的热力和机械强迫作用才使亚洲季风首先在孟加拉湾地区出现。ＢＯＢ季风环流提供了有利的背景条件，使ＳＣＳ季风接着爆发。最后随着亚洲热带流型的西移，印度季风爆发才发生。

The ECMWF (European Centre for Medium-Range Weather Forecasts) analysed data, the ECMWF/TOGA complementary data, the Climate Analysis Center/NMC (National Meteorological Center) outgoing long-wave radiation (OLR) data set, and the data set of China rainfall collected from 336 stations and archived at the Data Centre of the Institute of Atmospheric Physics (DCIAP) for the period of seasonal transition in the spring of 1989 were employed to study the thermal characteristics of the Tibetan Plateau and its neighboring regions, and their impacts on the seasonal transition in the Asian monsoon area. Special attention is paid to the diagnosis of the temporal and spatial distributions of surface sensible and latent heat fluxes. Results show that in 1989, the whole procedure of the outbreak of Asian monsoon onset was composed of three consequential stages. The first was the monsoon onset over the eastern coast of the Bay of Bengal (BOB) in early May. It was followed by the onset of the East Asian monsoon over South China Sea (SCS) by May 20, then the onset of the South Asian monsoon over India by June 10. The BOB monsoon was directly linked to the thermal as well as mechanical forcing of the Tibetan Plateau. It then generated favorable environment for the SCS monsoon onset, Afterwards, as the whole flow pattern in the tropical Asia shifted westwards, the onset of South Asian monsoon occurd.