【作者】 何春；

【导师】 丁一汇；

【作者基本信息】 南京信息工程大学 ， 气象学， 2006， 博士

【摘要】 本文讨论了亚洲夏季风建立的季节进程及机制。结果如下: 1.印度洋夏季风最早爆发于热带东印度洋,其建立进程具有逐步推进的阶段性特征,并与80°-90°E越赤道气流的发展联系紧密。越赤道气流不断加强并向北推进,是促使热带东印度洋夏季风爆发和北推的一个先决条件,与印度半岛及其以南洋面由于强烈的地表热通量的加热作用所形成的气旋性环流的形成与发展有关。在3月底到5月下旬使得热带东印度洋西南风不断加强并阻碍了热带西印度洋地区西南风增长,导致越赤道气流首先出现在热带东印度洋。 2.气候学意义下孟加拉湾夏季风的建立进程表现为三个阶段和两次突然北跳:(1)西风及对流活动于第23候在孟加拉湾南端开始建立。(2)当中南半岛强对流发生之后,受凝结潜热强烈释放所造成的垂直不均匀加热作用影响,孟加拉湾气旋性环流迅速增强并导致湾内水汽强烈辐合,使强对流活动在湾内大部分区域爆发,从而在第28候发生第一次北跳。(3)受印度夏季风爆发影响第二次北跳在第31候发生。 3.中南半岛及其邻近区域强对流活动的爆发对印度夏季风爆发具有重要作用。中南半岛强对流活动爆发使中南半岛-南海区域高层辐散运动增强及范围扩大,导致阿拉伯海-阿拉伯半岛区域高层辐合中心西移中东和北非,从而使阿拉伯海区域对流层下沉运动减弱,下层反气旋性环流也快速减弱,北风减弱,有利于索马里急流越过赤道之后快速北移。急流左侧强烈的涡度增长有利于阿拉伯半岛热低压迅速增强,同时也有利于其北侧的阿拉伯海对流层低层位势高度降低。同时,阿拉伯海区域对流层出现高层增温、低层降温的加热场配置,也有利于对流层低层位势高度降低。在以上因素的共同作用下,阿拉伯海对流层低层位势高度降低,负的经向位势梯度增大,导致西风增长,同时增强了的阿拉伯半岛热低压也引导西风向东加速,导致印度夏季风在第31候爆发。 4.1979-2001各年亚洲夏季风的阶段性爆发时间的推进顺序与上述气候学研究结果基本一致,表明热带东印度洋夏季风的建立确实在整个亚洲夏季风建立进程中处于重要的地位。同时夏季风在亚洲各区域的爆发时间存在较大的年际变化,同一地区各年的爆发形态也不相同。 本文的研究结果表明亚洲夏季风各子系统之间存在着密切的相互联系和相互作用。更多还原

【Abstract】 The seasonal process and mechanisms of onset of the Asian summer monsoon are investigated in this study, and the conclusions are as followed:1. The earliest onset of the Asian summer monsoon occurs over the tropical eastern Indian Ocean, which is mainly characterized by a stepwise advance, which is closely related to the evolution of the cross-equatorial flow. It will provide a precondition for the onset and the northward advance of the summer monsoon over the tropical eastern Indian Ocean when the cross-equatorial flow strengthens continuously and advances northwards, which is relative to the cyclone circulation caused by the heating of the strong surface sensible heat flux over the Indian Peninsula and the surface latent heat flux over the ocean to the south of it. The cyclone circulation is in favor of the continuous intensification of the southwesterly over the tropical eastern Indian Ocean but has an opposite effect on the counterpart over the tropical western Indian Ocean from the end of March to late May, and as a result the cross-equatorial flow takes place the earliest over the tropical eastern Indian Ocean.2. Three stages and two abrupt jumps exist in the climatological onset process of Bay of Bengal (BOB) summer monsoon: (1) on Pentad 23, westerly and convection start to build up in the southeastern part of BOB. (2) When the active convection emerges over the Indochina Peninsula, affected by the vertical asymmetric heating caused by the great amount of condensation latent heat release, the BOB cyclone circulation intensify rapidly as well as the moisture converges greatly in the BOB, which results in the active convection over the most areas of the BOB and the first jump appears on Pentad 28 consequently. (3) Influenced by the onset of the Indian summer monsoon, the second jump is found on Pentad 31.3. The onset of the vigorous convection over Indochina Peninsula and its adjacent areas is of very importance to the onset of the Indian summer monsoon. In consequence of the active convection over the Indochina Peninsula, the divergence at upper levels over the Indochina Peninsula-South China Sea intensifies and extends, then the convergence center over the Arabian Sea and the Arabian Peninsula comes to a westward shift, in such a way the subsidence in the troposphere over the Arabian Sea weakens, so does the low-level anticyclone circulation and the northerly wind, which makes for the fast northwards advance of the Somali jet flow after crossing the equator. While the significant increase of the vorticity on the left side of the jet flow is in favor of the rapid intensification of the heat low over the Arabian Peninsula and the lowering of the low-level geopotential height over the Arabian Sea, further more, the heating field with heating at upper levels and cooling at lower levels over the Arabian Sea also favors the lowering of the lower-level geopotential height. Affected jointly by the factors mentioned above, the low-level geopotential height lowers over the Arabian Sea, thus the negative meridional geopotential gradient strengthens and the westerly develops. At the same time the strengthened heat low over the ArabianPeninsula also leads to an eastward acceleration of the westerly, so the Indian summer monsoon onset starts on Pentad 31.4. The timing of the stepwise onset and advance of the Asian summer monsoon from 1979 to 2001 is identical to the result from the climatological analysis, indicating that the onset of the tropical eastern Indian Ocean acts as a very important role in onset process of the Asian summer monsoon. Great interannual variability appears in the onset timing of the Asian summer monsoon subsystems and their onset behaviors differ in different years.The results of this paper suggest that close relationships and interactions exist between the subsystems of the Asian summer monsoon.更多还原