飑线发展过程中回波合并的特征分析

Analysis of echoes merging characteristics during squall line development process

摘要:

基于区域自动气象站资料、济南新一代多普勒天气雷达资料，对2012年8月18日山东省境内飑线发展过程中对流单体之间以及弓形回波与对流单体之间的合并特征进行了细致分析。结果表明：1）合并过程经历了合并初期、合并中期和完全合并期。云桥位于雷暴中层，合并过程中回波强度先减弱再增强。2）合并的结果是，上游回波减弱并入下游回波，为下游回波提供了丰富的水汽，产生的下沉出流与暖湿空气辐合，增强了下游回波的上升运动，促使下游回波持续发展并替代老回波（属喂养型合并）。合并促使低层小尺度涡旋强度增强、底高降低，出现中气旋或非相关切变。3）对流单体与单体合并中期，两者强度减弱，完全合并期则强度增强。低层涡旋尺度小、强度强，中气旋或非相关切变的垂直伸展厚度和最大切变值较大、底高低，产生的龙卷持续时间长、影响范围大、造成灾害重。4）弓形回波与对流单体合并过程中，单体一直处于发展阶段，弓形回波在完全合并期减弱。低层涡旋尺度大、强度弱。5）龙卷的强度与中气旋或非相关切变的底高、垂直伸展厚度及最大切变值有关。单体合并过程中，若中气旋（或非相关切变）的底高或最大切变的高度降低，或者最大切变值出现跃增，则可能出现龙卷。弓形回波顶点附近有对流单体合并，易出现龙卷。

关键词:飑线;龙卷;后向传播;合并;跃增;中气旋

Abstract:

A squall line is formed in Shandong province,which is influenced by the high trough and surface convergence line in the afternoon 18 August 2012.Based on the automatic weather station data and Jinan Doppler Weather Radar data,this paper studies the merging characteristics of mergence between cell and cell,bow echo and cell during the development of the squall line.Results indicate that:(1) Merging process experiences the primary phase,the intermediate phase and the complete combined phase.The cloud bridge emerges at the middle level of the storm.The echo intensity first decreases and then strengthens during the merging period.(2) The results of the mergence are that the upstream echo decreases and merges with the downstream echo,and provides the abundant water vapor for the downstream echo.The convergence between downdraft outflow and warm moisture air increases the ascending movement of the downstream echo,so the downstream echo develops continuously and replaces the old echo.That is,the mergence belongs to the feeder type.The low level small scale vortexes are strengthened and their base heights reduce because of the mergence,so the meso-scale cyclone or uncorrelated shear is produced.(3) The intensity of two cells weakens during the intermediate merging phase of cell with cell,and strengthens during the complete combined phase.The low vortexes have the characteristics of small scale and strong intensity,the vertical stretching thickness and maximum shear value of the meso-cyclone or uncorrelated shear are larger,and their base heights are lower.The tornado storm expresses characteristics such as long duration,large influenced area and higher intensity,and can cause more serious disasters.(4) The cell maintains development during the entire merging period between the bow echo and cell,while the bow echo decreases in the period of complete combined phase.The low vortexes have larger scale and weaker intensity.(5) The base height,vertical thickness and maximum shear value of the meso-cyclone or uncorrelated shear show high relativity to the intensity of tornado.During the merging process of cells,when the base height or the maximum shear height of the meso-scale cyclone or uncorrelated shear reduces,or the maximum shear value increases abruptly,the tornado would be produced.If the mergence is located in the apex of the bow echo,the tornado would be produced.

Key words:squall line;tornado;back propagation;mergence;abrupt increase;meso-cyclone