中国东部副热带夏季风降水的准双周振荡及其可能维持机制

Quasi-Biweekly Oscillation of the Subtropical Summer Monsoon Rainfall over East China and Its Possible Maintaining Mechanism

利用1958—2007年中国740个测站逐日降水资料,定义了中国东部副热带季风降水区域。在此基础上对该地区夏季降水季节内振荡特征进行了分析,结果表明：中国东部副热带夏季风降水（SMR）具有显著的10-20天振荡（准双周振荡）周期,其传播基本表现为局地振荡特征;在年际尺度上SMR总量与准双周振荡的强度有密切关系。进一步利用1958—2007年NCEP I逐日再分析资料,分析了SMR准双周振荡维持的机制,发现SMR的准双周振荡与西太平洋对流扰动及其激发的低层低频环流场有密切关系,后者在Rossby波和环境流的共同作用下向西北方向移动是SMR准双周振荡维持的主要原因。

This study begins with the definition of the subtropical summer monsoon rainfall （SMR） region over East China by using the daily precipitation data at 740 stations of China during 1958--2007. Based on this definition, the quasi-biweekly oscillation （QBWO） of the SMR is investigated. The results show that a 10~20 d period is obvious and important in the intraseasonal cycle of SMR. Its propagation has characteristics of local oscillation. The related analysis shows that the total SMR has close relatiOnship with its QBWO intensity in interannual time scale. Further, the possible maintaining mechanism of QBWO in the SMR is discussed by using daily NCEP I reanalysis data during 1958--2007. It is found that the QBWO in the SMR is closely related to the convective disturbance over the West Pacific ocean and the low- frequency circulation in the low level triggered by the above convection. The latter moves northwestwards under the unified effect of Rossby wave and the environmental flow, which might be the main reason maintaining the QBWO in the SMR.