湖南娄底“6·20—21”强降水的中尺度特征分析

Analysis of the Mesoscale Characteristics of a Severe Rain on June 20 to 21,2015 in Loudi,Hunan Province

利用常规气象观测资料、NCEP/NCAR再分析资料和FY-2G的逐小时TBB资料,从卫星云图、环流背景、切变线的中尺度系统的演变以及产生的物理条件对娄底2015年6月20—21日强降水天气过程进行研究。结果表明:该次强降水天气过程主要是由中尺度对流系统活动造成的;强降水与地面风场辐合有很好的对应关系,强降水中心出现在辐合中心附近,但强降水发生要滞后于地面风场辐合形成。高空低槽发展、高低空急流的配合,西南低涡东出加强,是该次强降水天气发生的有利环流背景场,低空急流发展最旺盛时期对应着降水最旺盛时期,此外,中尺度对流系统持续长时间的影响是在有利的动力、热力和水汽条件下形成的。

Using the conventional meteorological observations, NCEP/NCAR reanalysis data and hourly TBB data from the Chinese weather satellite FY-2G, we studied the process of a severe rain that occurred on June 20 to 21 June, 2015 in Loudi based on satellite imagery, circulation background, the evolution of a mesoscale system on a shear and resultant physical conditions. The result is shown as follows. The rain was mainly caused by the activity of a mesoscale convective system. The intense rain was well corresponding with the convergence of a surface wind field such that the centre of the hard rain was in the proximity of the converging centre, though the occurrence of the former lagged behind that of the latter. Favorable circulation background fields include the development of an upper-level trough, the allocation of both the upper-and low-level jet streams and the eastward progression and strengthening of a southwest-China vortex. The most vigorous phase of the low-level jet stream corresponded with the time of the most severe rain. Besides, the observed sustained duration of the mesoscale convective system was generated under favorable dynamic, thermodynamic and water vapor conditions.