渤海湾海风锋触发雷暴的观测和模拟分析

Analysis on the Observation and Simulation of Thunderstorms Triggered by Sea Breeze Front in Bohai Bay

利用天津多普勒天气雷达观测资料和中尺度数值模式,对比分析了2007年8月13日海风锋触发雷暴天气的发生、发展演变特征。结果表明,数值模拟和多普勒天气雷达观测海风锋起始生消时间、形态特征和位置基本吻合。数值模拟能够更清晰地显示海风锋的物理量特征,也能反映出海风锋前端是东南风和东北风交汇的辐合带,在850 hPa以下向内陆推进过程中呈气温降低和湿度增加的特点,并逐渐形成增厚的热内边界层。从水汽和温度的水平分布来看,海风锋前端为温度和湿度等值线的密集区,海风锋背后为冷湿气团。另外,虽然未能模拟出阵风锋的细线回波,但模拟出阵风锋为干冷气流。雷暴四周均存在低层辐散下沉气流,只是雷暴主体前部阵风锋的辐散气流较强,而多普勒天气雷达仅能观测雷暴主体前部的阵风锋。多普勒天气雷达探测海风锋与阵风锋碰撞后,在碰撞交叉处形成雷暴天气,数值模拟揭示了碰撞交叉处形成雷暴天气的物理量特征,即:有明显的垂直运动和散度特征;广义理查逊数的分布特征也较显著,其厚度在1.0 km左右,CAPE值明显增加。

Using the Tianjin doppler radar data and the meso-scale numerical simulation method,the occurrence,developing and evolution characteristics of the thunderstorms triggered by the sea breeze front on 13 August 2007 was analysed. The results show that: The simulation not only reproduced the formation and dispersion times,morphological characteristics and locations of sea breeze front reasonably well,but also presented the physical characteristics of sea breeze front more clearly. Sea breeze front was the cross belt which converged northeaster and southeaster. Temperature decreasing and moisture increasing occurred under 850 hPa on the way of sea breeze front moving toward inland. Thermal inner boundary layer also formed behind the sea breeze front and its thickness increased as close to the sea breeze front. From the horizontal distributions of temperature and water vapor,the fore-end of the sea breeze front was the area with dense temperature and humidity gradients,while the behind was cold and moist air mass. In addition,the simulation reproduced the relatively cold and dry air and the sinking divergence motion at low level behind the gust front although the narrow radar echo line associated with gust front was not able to be simulated. Thunderstorms were more likely to form at the crossing point of the collision between gust front and sea breeze front,where convergence and upward motion were more favorable to maintain and rich CAPE and dynamic instability were provided.