MJO对春季中国东部大气环流和降水的影响

利用再分析资料分析了MJO（Madden-Julian Oscillation）不同位相对春季中国东部降水的影响。结果表明：MJO处于位相3时对应长江及其以南地区降水增多，处于位相7时该区域降水减小。当热带MJO对流从位相1东传至位相4，与其相伴的北向辐散辐合流会在印度东北部—长江及副热带西北太平洋地区的对流层中低层产生明显的辐合异常，且在MJO位相3时中国东部的辐合异常达到最大。从Rossby波源角度分析，这种辐合异常会增强对流层中低层气旋性环流，导致MJO处于位相3时长江流域及其以南地区降水增多。同时，利用现代次季节和季节预报业务系统探讨了MJO与降水的关系对降水预报技巧的影响，发现预报降水和再分析产品的相关系数在MJO处于位相3和7时有所增加。

Impacts of the Madden-Julian oscillation on springtime atmospheric circulation and rainfall over East China

The impacts of MJO on springtime precipitation over East China has been analyzed with reanalysis data. It is found that rainfall tends to increase in MJO phase 3 and decrease in phase 7 over Yangtze River and its southern area. The circulation anomalies associated with the rainfall changeswith MJO phases appear to be linked to a zonal band of atmospheric convergence anomalies in mid-to-lower level atmosphere extending from northeast India to Yangtze River and the subtropical West Pacific when the tropical MJO convection moves eastward from phase 1 to 4. The convergence anomaly reaches maximum in MJO phase 3 over East China. The convergence will induce a cyclonic Rossby wave source through the vortex stretching term, promoting cyclonic circulation in mid-to-lower level atmosphere over East China. This provides a dynamical explanation linking the tropical convection anomaly and the rainfall increase over Yangtze River and its southern area during MJO phase 3. The impact of MJO phases on rainfall prediction skill has also been investigated in a modern sub-seasonal to seasonal prediction system. The correlation between rainfall from the reanalysis and from the prediction tends to increase in MJO phases 3 and 7 when the MJO impact is the strongest.