干侵入对济南“7．18”暴雨的作用

Impacts of the Dry Intrusion on Ji'nan Torrential Rain Occurring on 18 July 2007

利用NCEP/NCAR再分析资料对2007年7月18日发生在济南地区的短时大暴雨过程进行了详细的分析,发现这次强降水过程是在高空槽和低空风切变的有利形势下产生的。济南附近最大干空气侵入出现在暴雨发生前1～2天,干空气侵入有利于深厚干层的形成和维持,而深厚干层的存在则有利于对流有效位能在中高层的产生、积聚和释放,从而导致强的对流上升运动,为暴雨的产生提供了条件。济南以北地区干空气侵入现象在暴雨过程中一直存在,主要有两种表现形式:对流层顶附近向下的干空气侵入和对流层低层由北向南的干空气侵入。济南外的干侵入一方面有利于低层产生辐合、高层产生辐散,导致上升运动的发展,另外一方面还对锋区的形成和移动具有重要作用。上述两方面表明干侵入在这次暴雨过程中起到了至关重要的作用。

By employing the NCEP/NCAR reanalysis data,the authors have analyzed the detailed characteristics of the Ji＇nan torrential rain occurring on 18 July 2007,the results show both the upper-level trough and the low-level wind shear are helpful to the occurrence of the torrential rain event.The most severe dry air intrusion around Ji＇nan occurs 1-2 days ahead of the torrential rain event,the dry air intrusion is advantageous to the formation and maintenance of the thick dry level.The thick dry level can lead to the generation,accumulation,and release of the Convective Available Potential Energy（CAPE）,and then,it can cause the convective upward air motion which can provide an advantageous condition to the occurrence of the torrential rain.On the north of Ji＇nan,the dry air intrusion phenomenon can be always observed during the torrential rain event,it has two modes：in the lower troposphere,the dry air from the mid-high latitudes can arrive in Ji＇nan;in the upper troposphere,the dry air from the upper levels can be extended into the lower troposphere.The dry air intrusion beyond Ji＇nan can cause the divergence in the lower troposphere and convergence in the upper troposphere,it can also influence the formation and moving of the front,and both the two aspects show that the dry air intrusion play an important role in the torrential rain event.