热带地区100hPa东风气流的气候效应(Ⅱ):与华北夏季降水的关系

Climatic Effects of 100 hPa Easterly Air Flow in Tropical (Ⅱ): Its Relationship with Summer Rainfall in North China

利用1954—1998年NCAR/NCEP再分析资料及同期我国160个测站月降水资料,分析了热带地区100hPa东风与华北夏季降水之间的关系。结果表明:(1)从春季到夏季,东风强度与华北夏季降水具有显著而稳定的正相关关系。(2)弱东风年夏季,印度洋及印度次大陆表面温度均为正异常,然而赤道印度洋地区的正异常明显强于其南北两侧。海温异常的这一分布特征,一方面使得100hPa东风减弱;另一方面使得南亚地区海陆热力对比减弱,导致南亚夏季风偏弱,进而造成由该季风区向华北地区的水汽输送减少,华北地区干旱。

Based on the NCEP/NCAR reanalysis datasets from 1954 to 1998 and the monthly rainfall data of 160 stations in China at the same time, the relation between the intensity of the tropical easterly on 100 hPa and summer rainfall in North China has been studied. The results are as follows： （1） The easterly intensity has a sustainable positive relationship with summer rainfall over North China from spring to summer. （2） In the weak easterly year, the anomaly of the surface temperature of the Indian Ocean is symmetric to equator which the maximum anomaly locates in. Namely, the anomaly of the surface temperature at equatorial Indian Ocean is stronger than that at the North Indian Ocean and the India subcontinent. This kind of distribution of surface temperature weakens the easterly on 100 hPa, on the other hand, it also decreases the sea-land heating contrast which makes the south Asia summer monsoon weaken. Furthermore, water vapor transportation from the South Asia monsoon area to the North China decreases. As a result, the rainfall is less than ever over North China in weak easterly year.