2013年7月31日京津冀飑线过程的数值模拟与结构分析

利用WRF (Weather Research and Forecasting Model)模式对2013年7月31日发生在京津冀的一次飑线过程进行了高分辨模拟,对比分析表明模拟结果和实况观测较为一致,因此,利用模拟结果分析得到的飑线结构和发展过程基本可信。模拟飑线系统的探空曲线再现了国外的研究得到的飑线系统具有的经典探空结构,如:层状云区接近饱和,尾流低压区具有"洋葱型"探空结构,以及尾流低压区之后与后方入流相联系的中层干区等。对该次飑线系统的风场、气压场进行的分析揭示出本次飑线过程在成熟阶段气压场呈"低高低"的不对称结构分布。其中,中高压有两个,分别位于飑线北部和中部的对流云区后方。尾流低压较弱,位于飑线中部层状云区后方。飑前低压位于飑线前偏南。飑线在成熟时期前方低层有一支入流,在飑线前部对流云区抬升后分为三支,分别向前方高层、后方高层和后方低层流出。同时后方中层有明显的后方入流,入流同时下沉到近地面辐散流出。对该次飑线的地闪特征进行的统计表明"起电层"中的冰相粒子混合比分布与地闪活动的特点可能有联系。本文的结果对于揭示华北飑线的中尺度结构具有重要参考意义,为进一步研究该次飑线的发生发展机理奠定了基础。

Numerical Simulation and Structural Analysis of a Squall Line That Occurred over the Beijing-Tianjin-Hebei Region of China on 31 July 2013

A high-resolution simulation of a squall line that occurred over the Beijing-Tianjin-Hebei region of China on 31 July 2013 was carried out using version 3. 5 of the WRF (Weather Research and Forecasting) model. The simulation reproduced many of the features of the squall line quite well, and thus facilitated further analysis of the structures and evolution of the squall line. The simulated vertical sounding of the squall line was consistent with similar studies performed by other researchers in the international science community;for instance, the near saturated sounding within the stratiform region, the "onion shaped" sounding within the wake low, and the mid-level low relative humidity sounding linked to the rear inflow behind the wake low. The study showed that the pressure field of the squall line appeared to be "low-high-low" in its mature stage. Namely meso-highs were located in the northern and middle parts and slightly lagged the convective region. A weak wake low existed at the back of the middle part of the stratiform region and there was a pre-squall low in the front of the southern part of the squall line. In its mature stage, a low-level inflow approached the squall line from the front, ascended in the convective region, and then split into three branches:a leading overturning updraft, an ascending front-to-rear updraft, and a descending front-to-rear downdraft. Besides, a strong rear-to-front inflow descended from the mid-level and diverged as it approached the ground. The characteristics of cloud-to-ground (CG) lightning activity in the squall line were also analyzed. The diagnosis revealed that the mixing ratio of ice-phase particles in the "charging zone" might be linked to the CG lightning. The results presented here are significant in revealing some of the mechanisms involved in squall lines occurring over North China, and lay the foundations for further studies on the development of such phenomena.