Abstract:

Based on NCEP reanalysis data, observational precipitation from automatic weather stations and the sounding and Doppler radar echo data in Wuhan of Hubei Province, the characteristics of environment fields of a squall line process occurring in Wuhan on 26 July 2011 were analyzed and simulated by WRF. The results showed that the squall line process took place under the condition of weak ambient vertical wind shear and strong convective instability. Two strong convective lines existed in the system during the squall line formation period. The simulated results about the left squall line developing and enhancing gradually showed that the vertical shear of environment wind was weak at the beginning of the squall line formation, and the strong unstable stratification in the front of the squall line played an important role on developing and strengthening of new cells. Thereafter, the unstable energy released gradually, but the vertical wind shear at low-level troposphere strengthened along the direction of squall line development due to the horizontal momentum being perpendicular to the squall line transported along the inverse gradient direction, which provided dynamical condition for the squall line development. During the squall line development peroid, the new cells constantly formed, enhanced and merged in front of the convection areas, which was the key factor of the squall line system maintaining for a long time, while the mature cells weakened and became stratiform precipitation cloud area, just so the system of squall line transmitted forward.

Key words: squall line, numerical simulation, convective instability, low-level vertical wind shear

摘要：

利用NCEP再分析资料、国家级自动气象站降水资料、武汉探空和多普勒雷达回波资料，借助WRF模式，对2011年7月26日发生在湖北的一次飑线过程进行环境场分析和数值模拟研究。结果表明：此次飑线发生在弱的垂直风切变和强对流不稳定环境下。飑线形成阶段，系统内存在左、右2条强对流回波带。对不断发展增强的左支回波带进一步模拟发现：初期，环境风垂直切变较弱，飑线前部强不稳定能量是飑线新生单体不断发展加强的主要原因；此后，不稳定能量逐渐释放，垂直于飑线系统水平动量的垂直逆梯度输送使得与飑线发展方向平行的对流层低层风垂直切变增强，为飑线发展提供动力条件。在飑线发展过程中，新生单体不断在对流区前沿触发加强以及对流单体合并与增长使得飑线系统得以长时间维持，而成熟单体减弱为后方的层状云降水区，正是单体的生消交替保证飑线系统向前传播。

关键词: 飑线, 数值模拟, 对流不稳定, 低层风垂直切变