1979年5月东南亚夏季风的建立和青藏高原的作用

Onset of the Southeast Asia Summer Monsoon in 1979 and the Effect of the Tibetan Plateau

东南亚夏季风开始于５月，它是大气环流向夏季环流过渡的一个重要阶段。本文用ＦＧＧＥ－ＩＩｂ全球网格点资料，分析１９７９年４月２６日到５月２５日，大范围（４０°Ｓ～５０°Ｎ，３０～１６０°Ｅ）温度、湿度和风场变化特征，计算了垂直速度、辐散风场、热源和水汽汇收支，研究了东南亚夏季风的性质和来源，其中着重分析了青藏高原的热力和动力作用与东南亚夏季风建立的关系。东南亚夏季风建立的主要因素是中纬度的环流形势，来自热带海洋的西南气流和青藏高原的作用。东南亚夏季风开始时，高空大气环流发生调整，青藏高原上空为波脊，两侧为波槽。低空东南亚夏季风区的辐合气流有四个来源：１）同经度范围的偏南辐散风，２）高原南侧的偏西辐散风，３）高原东侧的偏北辐散风，４）西太平洋上的偏东辐散风。分析表明，东南亚夏季风降水受高原西南侧的中纬度西风带波动影响。低空西南气流来源于８０～１２０°Ｅ的南半球热带地区，西南气流输送水汽并且加强低空辐合。主要的热源位于东南亚，主要是潜热释放形成的，它是驱动东南亚夏季风环流的主要机制。整个分析期，青藏高原是一热源，抬升的感热加热和动力作用形成和维持了高原上空的高压脊和两侧的波槽，从而有助于东南亚夏季风的建立。

The Southeast Asia summer monsoons (SE Asia monsoon) normally taking place in May has been recognized as the first seasonal transition stage from spring to summer. In this paper, utilizing the twice-daily FGGE-IIIb grid point data set in the area 40°S～50°N, 30～160°E, from 26 April to 25 May, the temperature, moisture and wind fields are analysed. Through caculating the divergent wind and heat and moisture budgets, the characteristics and the original sources of the SE Asia monsoons are discussed with an emphasis on the dynamic and thermodynamic effects of the Tibetan Plateau. The major factors responsible for the establishment of the SE Asia monsoon are the certain flow pattern distributed in mid-latitudes, the southerly flow originated from tropical ocean area and the influences of the Tibetan Plateau. During the onset of the SE Asia monsoon, there is a dramatic circulation adjustment process of westerlies occuring at the 200 hPa, resulting in a large amplitude ridge staying over the Plateau and troughs each on the west and lee side of the topography. It is found that four branches of divergent air streams coming from differently original sources contributed to the intense convergence in Southeast Asia: 1) the southerly divergent airstream between 80～120°E; 2) the northwesterly divergent wind flowing along the western flank of the Plateau; 3) the northeasterly divergent airstream along the eastern periphery of the Plateau; 4) the easterly divergent wind over the west Pacific Ocean. The disturbances in southern branch of westerlies along the southwestern flank of the Plateau induce the SE Asia monsoon rainfall. The southwestlies over the Southeast Asia is from tropical ocean area of the Southern Hemisphere. The roles of low-level southwestly flow transports the moisture air and increases dynamic convergence. The intense heat source over Southeast Asia due to the release of latent heat in association with the monsoon precipitation is the main mechanism of driving the circulation systems of the SE Asia monsoons. The heat source dominates throughout the entire analysed period over the Plateau. he sensible heating and the dynamic effect are favorable to the establishment and maintenance of the ridge over the Plateau and the troughs on the west and lee side of the topography.