华南及邻近海域春季海陆温差减弱与东亚夏季风强度关系的分析和模拟

Analysis and Simulation of Relation of the Weakening Trend of Land-Sea Difference of Springtime Mean Surface Air Temperature in South China and Its Ambient Ocean and Intensity of East Asian Summer Monsoon

利用NCEP/NCAR再分析资料,计算了1948—2006年春季平均地面气温的线性变率,表明其在华南地区为负变率,而在南部海洋则为正变率,即华南及邻近海域的春季海陆温差具有明显的减弱趋势。合成分析表明,其与夏季东亚区域南风的减弱趋势存在一定的联系。采用第三代区域气候模式(ICTP RegCM3)进行了在春季增高华南陆地表面气温和降低南部海洋表面气温的理想状况数值模拟试验,进一步分析华南及其邻近海域春季海陆温差减弱趋势对东亚夏季风强度的影响。模拟结果表明,与控制试验相比,敏感试验模拟的夏季850 hPa风场在中国东部地区表现出南风减弱的特征(差值风场为北风),同时还可发现夏季中国东部及其以东洋面存在一个气旋性差值环流。因此,华南及其邻近海域春季海陆温差的减弱趋势对东亚夏季风强度可能具有一定的影响。

Using NCEP/NCAR reanalysis data, the linear change rate （LCR） of springtime mean surface air temperature （SAT） is calculated. It is found that the negative LCR is dominant in South China, but the positive LCR is mainly located on the ocean, i. e. , there exists a weakening trend of land-sea difference of springtime mean SAT in South China and its ambient ocean. The composed analysis result shows that this weakening land-sea difference of SAT is correlated with the weakened trend of summertime southerly in East Asia. According to the diagnostic result, ICTP RegCM3 is adopted to have a sensitivity numerical experiment with changed SATs in South China and its adjacent ocean （CST）. The aim is to further investigate the impacts of the weakening trend of land sea difference of the springtime mean SAT on the intensity of East Asian summer monsoon. Comparing with the control experiment （CTL）, the monthly wind field at 850 hPa in summer of CST shows an obvious feature with decreasing southerly in eastern China （the difference of CST-CTL is northerly）. It atso can be found that a cycle circulation locates over the eastern China and its neighboring ocean from the difference field of wind at 850 hPa, which is maybe related with the variations of the West Pacific Subtropical High in CST. Furthermore, the ＂increasing in Southern and decreasing in Northern China＂ change of summertime precipitation in the eastern China could be simulated in CST. Summing up the above results, the weakening trend of land-sea difference of springtime mean SAT in South China and its adjacent ocean have certain influences on the intensity of East Asian summer monsoon.