太平洋中低纬度海表温差与副热带高压异常的数值模拟

Numerical simulation of the relationship of the anomaly of the subtropical high over the western Pacific with the difference of the sea surface temperature between mid and lower latitudes.

中国夏季天气变化与太平洋副热带高压关系密切,而中低纬度热力差异可能是副热带高压的强度和位置发生变化的重要原因,文中利用NCAR/NCEP再分析位势高度、垂直速度和海表温度场资料,在对太平洋海表温度合理分区的基础上,根据海表温度EOF分解的第一模态时间系数与副热带高压的相关关系,定义了太平洋中、低纬度海表温差指数,并通过统计分析和数值模拟方法分析了温差的年代际变化特征及其对副热带高压的影响。结果表明:副热带高压的变化分别与中纬度太平洋的(30°-40°N,180°-140°W)和低纬度太平洋的(10°S—10°N,140°-100°W)两块区域海温关系密切,对由此两区域定义的温差指数分析发现,1976年前后温差指数出现一次显著的由弱变强的年代际突变,且温差的年代际变化特征与副热带高压异常有很好的对应关系,温差大值年,副热带高压偏强,面积增大,西伸尤其明显;温差小值年,副热带高压偏弱,面积减小,东撤明显。进一步的统计分析和NCAR/CAM3.0模式数值模拟都发现,夏季中低纬海表温差增大将引起哈得来环流加强,副热带的下沉速度加大,使副热带高压增强;夏季中低纬海表温差减小将引起哈得来环流减弱,副热带的下沉速度减小,使副热带高压减弱。因此夏季中低纬海表温差的变化是导致副热带高压强度和位置异常的重要原因之一。

The summer weather in China is closely related to the subtropical high over the western Pacific（SHWP）.The thermal contrast between the mid and lower latitudes could be the main factor to influence the strength and location of the SHWP.The first EOF mode of the sea surface temperature（SST） is derived and the correlation of the SST and the SHWP is investigated by using the SST date and the geopo-tential height and vertical velocity front NCAR/NCEP reanaiysis datasct.Based on the above analysis two individual areas are selected.Then an index is defined to represent the difference of the SST（DSST） between the mid and lower latitudes over the Pacific.The index is highly correlated to the variation of the SHWP.The characters of the inter-decadal variability of the DSST and its impacts on the SHWP are studied by statistic method and numerical simulation.It is shown that the variation of the SHWP is associated with the SST over two regions（30°40°N,180°140°W） and（10°S- 10°N,140°- 100°W） respectively.There is an abrupt change of DSST from weak to strong around 1976 which is closely related with the change of the SHWP.When the DSST is larger,the SHWP is stronger,its domain is larger and can extend more westerly;when the DSST is smaller,the SHWP variation is on the opposite.The numerical simulations further show that increasing DSST will result in the enhancing of Hadley cell descent and the strength of the SHWP.As a result,the DSST is one of the main factors to influence the strength and location of the SHWP.