华南持续性强降水期间低频非绝热加热对低频环流的影响

The influence of the low-frequency diabatic heating on the low-frequency circulation during the persistent severe rainfall period over South China

中文关键词:  持续性强降水  非绝热加热  低频  华南

英文关键词:Persistent severe rainfall  Diabatic heating  Low-frequency  South China

中文摘要:

      利用站点降水资料和再分析资料针对华南地区5—8月的持续性强降水过程,分析了低频异常非绝热加热的时空分布特征及其对低频大气环流的可能反馈作用。得到如下结论:5—6月和7—8月华南持续性强降水期间10—30 d低频非绝热加热的演变特征有所不同,5—6月持续性强降水发生前低频非绝热加热大值区从30°N(107°—115°E)以北向南传播发展至华南地区,而在7—8月降水前非绝热加热大值区从中国南海中部向西北方向传播,并在降水最强盛期到达华南。异常环流型控制着持续性强降水的强度和位置,从而决定异常凝结潜热的演变特征。异常凝结潜热则是通过影响涡度倾向变化而对大气环流有一个反馈作用。对于发生在华南5—6月和7—8月的这2组持续性强降水过程,当降水处于发展阶段,在低频非绝热加热作用项和低频涡度平流项的共同作用下,华南上空中层存在显著的10—30 d低频正涡度倾向变化,有利于低频气旋式环流的进一步发展。非绝热加热作用项主要由加热率的垂直梯度决定,涡度平流项则与气候背景风场有密切关系。5—6月持续性强降水期间涡度平流项位于非绝热加热项东侧,而7—8月持续性强降水期间涡度平流项位于非绝热加热项北侧。在持续性强降水的衰亡期,由于非绝热加热项和涡度平流项转为负值,华南被负涡度倾向变化控制,低频气旋式环流迅速消亡。

英文摘要:

      This study investigates the distribution and evolution of the low-frequency anomalous diabatic heating and its effects on the low-frequency anomalous circulation on 10-30 d timescales, accompanied with the persistent severe rainfall (PSR) events over South China during May-August. The evolution of the anomalous diabatic heating during the May-June (MJ) PSR and July-August (JA) PSR is different. The low-frequency diabatic heating anomaly propagates southward from north of 30°N to South China over 107°-115°E before the MJ PSR events, while the anomalous diabatic heating propagates northwestward to South China from the South China Sea (SCS) and Philippine Sea before the JA PSR events. The anomalous circulation pattern could control the position and intensity of the rainfall and condensational heating, and the condensational heating could however give a feedback to the anomalous circulation by affecting the vertical vorticity tendency. For two groups of events (MJ and JA) over South China, the significant positive vorticity tendency anomaly on 10-30 d timescals is over South China under the influence of both the anomalous diabatic heating and the advection of vorticity during the rainfall developing period. The vertical nonuniform of the diabatic heating has an important influence on the vorticity tendency, and the vorticity advection is closely related with the mean state of the wind fields. The anomalous vorticity advection is located east of the anomalous diabatic heating during the MJ PSR events, while the anomalous vorticity advection is located north of the anomalous diabatic heating during the JA PSR events. The anomalous diabatic heating and vorticity advection turn to negative ones during the rainfall ending period, the negative vorticity tendency anomaly is over South China which is favorable for the decaying and ending of the anomalous cyclone.