北京地区雷暴阵风锋触发对流新生的环境场特征分析

Analysis of Environmental Field Characteristics of Convective Initiation Triggered by Thunderstorm Gust Fronts in Beijing Area

为了加强对雷暴阵风锋触发对流新生环境场特征的认识,利用北京地区常规探空观测资料、地面加密自动站、 S波段多普勒天气雷达及多种新型探测资料对北京地区雷暴阵风锋触发对流新生的两种典型个例的环境场特征进行分析。结果表明:(1)Ⅰ型为多条阵风锋相遇或阵风锋与其他边界层辐合线相遇,在高对流有效位能CAPE和高湿区域触发对流(即碰撞型触发)。此类型中,两条阵风锋相遇时产生了比单条阵风锋大得多的垂直速度,强烈的上升运动为对流触发提供了良好的抬升条件。(2)Ⅱ型为阵风锋移动至高CAPE区域触发对流(即非碰撞型触发)。此类型阵风锋在移动方向上与环境风有强辐合,同时,垂直于阵风锋剖面内的风分布有利于触发对流的上升气流倾向于竖直。(3)阵风锋触发对流新生的环境场中,用CAPE表示的深厚湿对流潜势普遍较未触发对流的个例高,对流抑制能量CIN低;大部分个例高层有干冷平流、低层有暖湿平流,垂直方向上的静力不稳定较强;大部分新生的对流出现在低层风向切变或风速辐合以及高CAPE地区。(4)未触发对流的个例中,环境场在垂直方向上的分布不利于对流的新生和发展,阵风锋经过的地区为辐散区或低CAPE高CIN的地区,动力和热力条件配合不理想,不利于对流触发。

In order to enhance the understanding of the environmental field characteristics of the convective regeneration triggered by thunderstorm gust fronts.Based on Beijing sounding observation,automatic stations,Sband Doppler radar and new detection data to analyse environmental field characteristics of two typical cases in which convection initiation triggered by thunderstorm gust fronts.The results show that:(1) One type is convection triggered by collision of multiple gust fronts or the encounter of gust fronts with other boundary layer convergence lines in the region with high Convective Available Potential Energy(CAPE) and sufficient water vapor(collision triggering).In this type,the vertical velocity of two collision gust fronts is much larger than that of a single gust front.Strong upward movement is easy to provide good lifting conditions for the triggering of convection,and convection is easy to trigger.(2) The other type is the gust front triggers convection in the unstable region(non-collision trigger).In this type,the low-level wind direction is perpendicular to the gust front,which is conducive to the strong convergence between the ambient wind near the ground and the gust front.Meanwhile,the updraft of the convection triggered by the gust front tends to be vertical,which is beneficial to convective initiation.(3) By comparing the environmental field of gust fronts trigger and non-trigger Convective Initiation(CI) cases,the results show that there are deep wet convection potential with high CAPE and low Convective Inhibition(CIN) of the environment field in these cases which CI are triggered by gust fronts.The wind profile and microwave radiometer observations indicate that there are cold dry advection at the upper level and warm wet advection at the lower level in most cases CI triggered by the gust fronts.In most cases which gust fronts trigger CI occur at the wind speed or wind direction convergence areas with high CAPE.(4) In cases which non-triggered CI,vertical distribution of environmental field is not conducive to the regeneration and development of convection,and gust fronts pass the area which are divergence or there are low CAPE and high CIN.These conditions are adverse to convection triggering.