热带大气季节内振荡对江西5月降水的影响

IMPACT OF THE MADDEN-JULIAN OSCILLATION ON PRECIPITATION OF JIANGXI IN MAY

利用实时的热带大气季节内振荡（MJO）指数和江西省83个台站降水资料，通过位相合成方法分析了MJO对江西5月降水的影响。（1）在强MJO第4—5位相（MJO活动中心位于赤道印度洋东部印尼群岛附近）江西降水为正异常，在第6～8位相（MJO活动中心位于西太平洋以东）和第1—3位相（MJO活动中心位于赤道印度洋）为负异常，其中以第4位相的正异常和第7位相的负异常最明显。（2）当MJO对流中心位于印尼群岛附近时，副高西伸脊点偏西，处于异常西南风控制，从西太平洋副热带地区向江西输送的水汽加强，位于水汽辐合区内，受上升运动控制，有利于江西出现降水。当MJO传播至西太平洋地区时，江西转为受异常偏北风控制，水汽输送减弱，为水汽辐散区，受下沉运动控制，不利于江西出现降水。

Impact of the Madden-Julian Oscillation （MJO） on the precipitation of Jiangxi province in May is investigated based on a real-time MJO index and observed daily precipitation from 83 gauge stations in the province during 1975-2010. The results show that Jiangxi precipitation in May showed differences at eight MJO phases. Positive precipitation anomalies occurred at phases 4- 5, where the main MJO convective body moved to Indonesia. Negative precipitation anomalies appeared at phases 6-8 when the main MJO convective body appeared east of the equator in the western Pacific, and at phases 1 -3 when it was situated over the Indian Ocean. The positive anomalies at phase 4 and the negative anomalies at phase 7 are the most significant. When the main MJO convective body moves to Indonesia, the northwestern Pacific subtropical high shifts more westward than normal. Water vapor transported from the northwestern Pacific subtropical areas significantly enhances the water vapor flux over Jiangxi, which is a water vapor convergent region with strong upward motion, resulting in the occurrence of the precipitation. When the main MJO convective body moves to the western Pacific, the northwestern Pacific subtropical high is weaker than normal, with its position extended slightly eastward. The wind in Jiangxi shifted to the north and transported smaller amount of water vapor to Jiangxi, which was controlled by divergent water vapor with downward motion to decrease the precipitation.