一次中亚低涡的动力热力结构及演变特征

Dynamic and Thermal Structure and Evolution Characteristics of a Central Asian Vortex

利用NCEP再分析1°×1°资料对2009年9月4-7日造成新疆西南部一次暴雨过程的中亚低涡的动力热力三维结构及演变特征进行了分析,并初步探讨了低涡的发生、发展机理。结果表明:此次中亚低涡具有明显的冷心结构且较为深厚,首先在对流层中高层发展(300 h Pa高度上低涡中心及演变特征最为明显),随时间向低层延伸,其发展—成熟—减弱过程是一个斜压—正压—斜压的过程。成熟期,300 h Pa之下均为冷异常,冷中心与高度中心相重合,轴线趋于垂直;低涡中心附近对流层整层均为正涡度区,在其东西两侧300 h Pa高度上存在对称的正涡度中心;低涡中心附近对流层低层辐合、中高层辐散的结构有利于上升运动及中亚低涡的维持发展。减弱期,冷中心强度明显减弱,轴线向西倾斜,低涡中心附近对流层中高层出现负涡度区,无明显辐散辐合和上升运动。此次过程中,上升运动与充足的水汽相互配合,引发强降水。对流层"上干下湿"的空间结构、冷空气向下传递以及高位涡的侵入和向下传递对低涡的发展演变有重要意义。

By using the NCEP 1° × 1° reanalysis daily datasets,the dynamic and thermal three- dimensional structure and evolution characteristics of a central Asian vortex causing rainstorm during 4 to 7 September 2009 were analyzed,and its development mechanisms were discussed. The results indicated that the vortex had an obvious cold core structure and developed strongly,which developed at the upper firstly( its center and evolution characteristics were evident on 300 h Pa) and extended downward with time,its development- mature- weakened process was a baroclinic- barotropic- baroclinic process. In mature stage,cold center coincided with height center with the axis tending to be vertical; there was a positive vorticity center on both western and eastern flank of vortex center on 300 h Pa which were symmetrical and the vorticity almost was positive in troposphere;the lower troposphere was convergence while the upper troposphere was divergence,making conditions favorable for ascending motion and vortex development. In weaken period,the axis- line tilted toward the west and cold center declined significantly; there was negative vorticity in the middle and upper troposphere and no obviously divergence / convergence and ascending motion in almost all of troposphere over vortex center. During this process,ascend motion combined with ample water vapor condition causing the heavy precipitation. The 'upper dry,lower wet'spatial structure in troposphere,the cold air moved downward as well as the intrusion and downward motion of high potential vorticity were conducive to the development of this vortex and played a significant role in its development and evolution.