山东省初秋一次大范围强对流过程落区和抬升触发机制分析

Analysis of an Extensive Severe Convection Falling Area and Lifting Trigger Mechanism in Early Autumn at Shandong Province

利用常规观测、加密自动站、多普勒天气雷达、风廓线雷达及NCEP再分析资料,对2016年9月11日山东省初秋大范围强对流天气的落区和抬升触发机制进行了分析。结果表明:受高空槽影响,有、无对流区上空大气层结均不稳定,大的对流有效位能(CAPE)与小的对流抑制能量(CIN)环境条件下,强对流云团呈现"遍地开花型",抬升触发成为强对流发生的关键因素。地面辐合线、干线、海风锋、冷池出流是主要的抬升触发系统。由于对流抑制小,抬升强迫一般不需要太强,不同区域雷暴的抬升机制不同,鲁西北地区强对流天气由地面辐合线抬升触发,山东半岛地区的对流是由海风锋与冷锋共同触发,而鲁中地区强对流则由老的雷暴的冷池前沿阵风锋抬升触发,鲁东南地区的对流是由干线与地面辐合线共同作用造成的。辐合线抬升强迫的大小很重要,其量化可通过边界层散度衡量。在同样具备地面辐合线的情况下,不同温湿性质气团的中尺度边界对雷暴触发起关键作用。预报落区的偏差主要是因为短期阶段无法获取低空东南风气流这一关键中尺度系统,不同起报时间模式预报的调整趋势、季节等因素是对流强度预报偏弱的主要原因。经验表明,通过对大量个例的分析研究,提高对数值模式的订正能力是提高预报准确率的有效方法。

Conventional observations,encryption automatic weather station,Doppler weather radar,windprofiling radar and NCEP reanalysis data are identified and examined to analyze the extensive severe convection falling area and lifting trigger mechanism in Shandong on 11 September 2016.The results show that under the influence of upper trough,unstable atmospheric stratification occurred over the regions whether or not convections,severe convective cloud cluster spread everywhere in the environments characterized by large convective available potential energy（CAPE）and little convective inhibition（CIN）,thus the trigger of lifting become the key factor for severe convection’s occurrence.Lifting trigger mechanism was organized by surface convergence line,dry line,sea-breeze front and gust flow.Because of the little convective inhibition,lifting force could be relatively weak causing various thunderstorm lifting mechanisms in different regions.Surface convergence line lifting caused the severe convection in Northwest Shandong,and the combination of sea-breeze front and cold front caused the severe convection in Shandong Peninsula.Gust front of the preexisting thunderstorm cold pool boundary was the reason of severe convection in midland Shandong,while the interaction of dry line and surface convergence line caused the severe convection in Southeast Shandong.The magnitude of convergence line lifting force which can be measured by boundary’s divergence was a consequential element.Under the condition of the surface convergence line,mesoscale boundary of mass in different temperature and humidity became the determining factor of thunderstorm trigger.The omissive forecast of the southeast low-level flow in short-term forecast which was a key mesoscale system caused the deviation of the forecast falling area.So,adjustment trend of model forecast in different initial times and seasons are the major reasons for the less intense forecast.Experience indicates that improving the correction ability of numerical model by analyzing a large number of cases is an effective method to raise the forecasting accuracy.