中南半岛地区热力特征对南海季风爆发的可能影响及机理

利用1998年5月1日－8月31日南海季风试验(SCSMX)产1980年1月－1995年12月NCEP／NCAR候平均再分析资料，分析1998年和多年平均情况下南海夏季风爆发期间中南半岛地区热力特征，揭示该地区热状况的异常与南海夏季风爆发之间的可能联系，从而讨论引起南海夏季风爆发的可能机制。结果发现，南海季风爆发前中南半岛附近地区存在较强的持续地面感知加热并具有显的低频振荡特征，低层大气在中南半岛地区出现较强的暖中心，由此导致局地强的水平温度梯度和位势高度梯度，有利于加强该地区的西南风。南海季风爆发前中南半岛地区低层出现较强的辐合风，高层出现较强的辐散风，这种低层强的辐合，高层强的辐射散配置有利于垂直运动的发展，降水的加强，进而触发南海季风的爆发。对多年平均资料的分析也证实了1998年南海季风爆发过程中所具有的特征，并进一步发现南海季风爆发前中南半岛地区850hPa温度是逐渐增加的，且增温幅度大于南海地区上空，由此加强了中南半岛与南海之间的温差。另外，比纬圈温度偏差和位势高度偏差的分析中发现，南海季风爆发期间南海和中南半岛地区的副高东撤与中南半岛地区的增温和孟加拉湾低槽的向东扩展有关。

Mechanism of thermal features over the Indo-China peninsula and possible effects on the onset of the South China sea monsoon

The thermal characteristics during the South China Sea (SCS) summer monsoon onset period near theIndo-China Peninsula are analyzed by using the South China Sea Monsoon Experiment (SCSMEX)reanalysis data from I May to 31 August 1998 and the NCEP/NCAR pentad-mean reanalysis data fromJanuary 1980 to December 1995. The possible relationships between the anomaly of thermal features nearthe Indo-China Peninsula and the SCS monsoon onset are investigated, and the mechanism causing theSCS summer monsoon onset is also discussed. Results from the 1998 SCSMEX reanalysis data show thatthere exists a strong persistent surface sensible heating near the Indo-China Peninsula prior to the SCSmonsoon onset, which has apparent low frequency oscillation features. This sensible heating leads to awarmer center in the lower atmosphere near the Indo-China Peninsula and strong local horizontal tempera-ture and geopotential height gradients which are favorable to strengthening the southwest wind over theIndo-China Peninsula. It is also found that stronger convergent winds at lower levels and stronger divergentwinds at high levels appear, which provide a favorable configuration for the development of vertical motion,enhancement of precipitation, and onset of the SCS monsoon. These results can be verified by analysis of themulti-year mean data. Additionally, it is found that the temperature at 850 hPa increases more rapidly overthe Indo-China Peninsula than the South China Sea prior to the SCS monsoon onset, which leads to astrengthening of the temperature difference between the Indo-China Peninsula and the South China Sea.Moreover, results from the analysis of the Iongitudinal temperature and geopotential height differencesshow that the eastern retreat of the subtropical high over the Indo-China Peninsula during the period ofSCS monsoon onset is associated with the temperature increase over the Indo-China Peninsula and theeastern extension of low trough over the Bay of Bengal.