亚洲南部地区海陆分布和南半球陆地对亚洲夏季风影响的数值试验

Impacts of Ocean-Land Distribution over the Southern Asia and the Continents over the Southern Hemisphere on the Formation of Asian Summer Monsoon Circulation

利用CCM3/NCAR模式,设定了几种海陆分布状况,将亚洲25°N以南地区以90°E为界分为东西两个部分,讨论东部陆地(中南半岛、海洋大陆和澳大利亚)和西部陆地(非洲大陆和印度半岛)存在对东亚季风环流系统和印度季风环流系统的影响,结果表明:(1)西部陆地的存在是印度季风环流系统形成的主要机制,而对东亚季风环流系统影响不大;(2)东部陆地的存在是东亚季风环流系统形成的主要机制,但它对印度季风系统也能产生影响;(3)孟加拉湾季风环流及其北部强降水中心是印度半岛和中南半岛存在联合造成的;(4)南半球的非洲和澳大利亚的存在所造成的环流是相互影响的;(5)中南半岛的存在是南海夏季风季节变化的主要机制,澳大利亚的存在有利于盛夏时强西风推进到南海。

The independent formation mechanism of India Monsoon Circulation System （IMCS） and East Asian Monsoon Circulation System （EAMCS） is investigated from the viewpoint of numerical simulations, which supports the diagnostic analysis results. The adopted model is CCM3/NCAR, in which five sea-land distribution scenarios are designed to demonstrate the impacts of the eastern/western continents of Asia south of 25°N with 90°E as the divide, and the one over the Southern Hemisphere, on the formation of IMCS and EAMCS respectively. Five sensitivity experiments are performed as follows： CTL （actual sea-land distribution test, i. e. , control test）, NAFINT （identical experiment with CTL except that the land grid points composing the continents west of 90°E, including Africa, Arabian Island and Indian Peninsula, have been removed and replaced by ocean grid points with sea surface temperature （SST） linearly interpolated from the surrounding existing ocean grid points）, NAUSICT （same as NAFINT but the removed land grid points are those composing the continents east of 90°E, including Indochina Peninsula, Maritime continents and Australia）, NSAFT （same as NAFINT except removing those land grid points composing the African continent south of the equator）, NAUST （same as NAFINT with the exception of removing those grid points composing Australia）. The conclusions are arrived at： Firstly, the presence of the sea-land thermal distribution comprised by the continents west of 90°E and adjacent marginal seas is chiefly responsible for the formation of IMCS but with few impacts on the EAMCS, in the absence of these continents, the major elements of IMCS, the Mascarene high and the southeasterlies north of it, the Arabian southwesterlies and the Somalia cross equatorial flows weaken dominantly, moreover, the southwesterlies over India and the associated monsoon trough circulation do not emerge any more, nevertheless the EAMCS remains to be observed obviously. On the contrary, the thermal sea-land distribution resulting from the continents east of 90°E and neighboring seas not only acts as an important role in the formation of EAMCS but also has effect on the IMCS to some extent. When these continents are removed, South China Sea （SCS） summer southwesterlies, circulation almost disappear, and the airflow from the the cross-equatorial flows and the related monsoon trough western Pacific to the mainland of China south of the Changjiang River also weakens remarkably, and meanwhile the IMCS fades away to a certain extent. Secondly, it is revealed that the formation of the Bay of Bengal （BOB） monsoon circulation and the corresponding intense rainfall center north of it are attributed to the coexistence of India and Indo-China Peninsula, the presence of India mostly responsible for the generation of south wind component of BOB monsoon, whereas Indochina Peninsula primarily for the west one. Thirdly, it proves that the circulation caused by the African continent over the Southern Hemisphere and the counterpart by Australian continent could interact with each other. And finally, the effects of the above continents on the seasonal variations of SCS summer monsoon are examined, indicating that the presence of Indochina Peninsula is the crucial mechanism that maintains the SCS summer monsoon seasonal variations, while the presence of Australia favors the strong westerly wind extending into SCS in midsummer.