秋季水汽输送特征及其与云南降水的关系

摘要

利用云南122个测站1961-2008年秋季（9-11月）降水量和同期NOAA提供的月平均再分析资料，分析了秋季各月降水与水汽通量、水汽通量散度的分布，以及环流异常对降水的影响。结果表明：11月降水场与水汽通量场和水汽通量散度场耦合程度最高，10月次之，9月最小。在降水的空间分布型上，云南秋季降水与水汽通量输送、水汽通量散度的相关基本为一致的正相关；秋季降水量场与水汽通量场的时间变化趋势一致，水汽输送通量、水汽通量散度的变化直接影响降水的变化。云南秋季降水的多少主要是环流异常引起，当云南9月降水正异常时孟加拉湾季风偏强，副热带高压偏弱偏东，冷空气活跃，反之则出现负异常；当10月降水正异常时南支槽和西南季风活跃，影响云南的偏南暖湿气流强盛，反之则降水偏少；当11月南支槽和影响云南的冷空气活跃，云南降水偏多，反之则出现负异常。在水汽净收支方面，9月纬向的净收入最大，而10月纬向的净收入减弱，11月在西风带的控制之下，纬向净收支非常小。而经向上的水汽收支在9-11月有从支出到流入的转换。从云南正负异常年整层和低层水汽净收支看，除11月负异常年为水汽源外，其他都为水汽汇。用ERA-Interim再分析资料与20 CR再分析资料计算的水汽误差较小，并且正负异常年水汽净收支变化一致。%Using the monthly autumn precipitation data of 122 observation stations over Yunnan Province from 1961 to 2008 and the NOAA monthly mean reanalysis data,distributions of monthly precipitation and water vapor fluxes and water vapor flux divergence in autumn,as well as the effect of atmospheric circula-tion anomaly on precipitation are analyzed.The results show that,there exists the best coupling relation-ship of rainfall and water vapor flux,water vapor flux divergence in November,while in October it is the second,and in September it is the worst.There is a positive correlation between autumn precipitation distribution,and water vapor flux and the divergence of water vapor flux in Yunnan.The autumn precipi-tation field is consistent with the time variation trend of water vapor flow field.The changes of water va-por flux and water vapor flux divergence directly affect the change of precipitation.The autumn precipita-tion amount is largely influenced by the atmospheric circulation anomaly.When September precipitation in Yunnan is abnormal,the monsoon in Bay of Bengal blows strongly,the subtropical high is by east and weak,and the cold air is active.Otherwise appears the negative anomaly.When rainfall in October is ab-normal,southern trough and southwest monsoon are active,strengthening Yunnan’s southerly warm and humid air flows,otherwise,precipitation is less.When in November the southern trough and the cold airs that influence Yunnan are active,more precipitation produces,otherwise,negative anomaly appears.Re-garding the vapor net budget,the zonal net income in September is the largest,while zonal net income in October weakens.In November,under the control of the westerlies,the net income becomes very small. However,meridional water vapor income during September to November transfers from expenditure to in-flows.Thinking from the whole-layer and low-level vapor net budget in positive and negative anomaly years in Yunnan,except for the November in negative anomaly years it is water vapor source,in all the other times it is moisture convergence.When calculating with ERA-Interim reanalysis data and 20CR rean-alysis data,the water vapor error is found small,and the vapor net budget variations in positive and nega-tive anomaly years are consistent.