青藏高原动力和热力作用对季节转换期全球大气环流影响的数值研究

NUMERICAL STUDY ON INFLUENCE OF THE QINGHAI-XIZANG TIBETAN PLATEAU ON THE SEASONAL TRANSITION OF THE GLOBE ATMOSPHERIC CIRCULATION

利用ＣＣＭ１（Ｒ１５Ｌ７）－ＬＮＷＰ模式，以１９９６年３月１７日的国家气象中心客观分析资料为初始场，分别采用有、无青藏高原两种方案，数值研究了青藏高原对５月份全球大气环流季节转换的影响。试验结果表明：北半球初夏，青藏高原区域用同纬度地区的一个中空热源，其作用可以在２００ｈＰａ层形成一个２２４Ｋ的暖中心，使大气增暖７Ｋ以上。高原地形的动力和非绝热作用使得南极大陆２００ｈＰａ层大部分地区降温６Ｋ左右，最大负中心可达－８．２８Ｋ，这对于南半球由夏至冬过程中，环极涡旋的强度加深和范围扩大是有利的。高原地形作用对北半球大气环流平均槽脊的形成和维持有十分重要的影响，它加强了高原所在纬度带北侧（减弱了南侧）由南向北的正温度梯度，同时也增强了３０°Ｓ附近由北向南的正温度梯度，从而有利于季节转换过程中全球中纬西风带的整体北移和初夏亚洲季风环流的形成。同时高原地形作用在赤道及低纬地区形成的位势增加区，有利于南半球热带高压脊的北退和北半球副高增强北移。此外，它还有利于南半球极地东风带的增强和５００ｈＰａ层环极低压带的强度减弱，同时增加了罗斯海附近的极涡强度。

In this paper,by employing the CCM1(R15L7)-LNWP spectral model,the influences of the Qinghai-Xizang Plateau on the seasonal transfer of the general circulation were studied.According to the initial of 17 March 1996,numerical experiments with and without orography are carried out respectively.The results show that the Qinghai-Xizang Plateau,as a heat source in middle of troposphere,produces a warm sector of 224K at 200hPa in May.The dynamic and diabatic heating effect caused by the plateau's huge orography decreases by 6K at 200hPa temperature in Antarctic.The biggest meions is -8.28K.This is favorable for the South Polar vortex to strengthen and widen from summer to winter.The orographic effect has a profound influence on the formation and maintenance of the northern hemispheric average trough and ridge.It makes the temperature gradient,near the plateau and 30°S,increase in the north and decrease in the sorth.It improves the northern shift of the mid-latitude westerly jet and subtropical high pressure belt,and plays an important role in the formation of meridional monsoon circulation in Asia.Moreover,the orographic effect strengthens the easterly wind belt over the Antarctic and polar cyclone near the Ross Sea,but weakens the South Polar low pressure belt at 500hPa.The appearance of cross-equatorial Somali jet relates to the effects of the Plateau,too.