热带季节内振荡对广东6月降水的影响

IMPACT OF TROPICAL INTRASEASONAL OSCILLATIONS ONTHE PRECIPITATION OF GUANGDONG IN JUNES

利用1979—2008年共30年广东省86个测站的地面观测逐日降水资料和NCEP-DOE第二套分析资料的大气多要素日平均资料,分析热带大气沿赤道东传的季节内振荡(MJO)对广东6月降水的影响及其物理过程。结果表明:6月MJO活动对广东降水的调制作用与前汛期(4—6月)期间其它月份不同,对6月广东省降水正(负)异常有指示意义的是强MJO事件的第3(第6)位相。当赤道MJO处于第3位相时,西太平洋副热带高压明显加强西伸,来源于西太平洋地区的水汽随副高边缘向广东输送明显加强,广东水汽通量明显增加,从而导致广东降水加强。而第6位相的情况基本相反。强MJO第3位相造成西太平洋副热带高压偏强偏西的物理机制与大气对东印度洋非对称热源的响应有关。2010年6月广东两次持续性强降水过程与MJO强度较强且处于第3位相这种活动状态密切相关,进一步证明赤道MJO活动对广东6月强降水的重要指示作用。该结果有助于拓展广东强降水的预报思路,结合动力模式产品将有助于延长预报时效。

The impact of tropical intraseasonal oscillations on the precipitation of Guangdong in Junes and its physical mechanism are analyzed using 30-yr （1979--2008）, 86-station observational daily precipitation of Guangdong and daily atmospheric data from NCEP-DOE Reanalysis. It is found that during the annually first rainy season （April--June）, the modulating effect of the activity of intraseasonal oscillations propagating eastward along the equator （MJO） on the June precipitation in Guangdong is different from that in other months. The most indicative effect of MJO on positive （negative） abnormal precipitation over the whole or most of the province is phase 3 （phase 6） of strong MJO events in Junes. A Northwest Pacific subtropical high intensifies and extends westward during phase 3. Water vapor transporting along the edge of the subtropical high from Western Pacific enhances significantly the water vapor flux over Guangdong, resulting in the enhancement of the precipitation. The condition is reverse during phase 6. The mechanism for which the subtropical high intensifies and extends westward during phase 3 is related to the atmospheric response to the asymmetric heating over the eastern Indian Ocean. Analyses of two cases of persistent strong rainfall of Guangdong in June 2010 show that both of them are relatively close to the MJO state, which is strong and in phase 3, besides the effect from a westerly trough. It is argued further that the MJO activity is indicative of strong rainfall of Guangdong in June. The results in the present work are helpful in developing strategies for forecasting and extending the period of validity when they are combined with the outputs of dynamic forecast models.