杨波,孙继松,刘鑫华. 2019. 两类不同风灾个例超级单体特征对比分析[J]. 气象学报, 77(3):427-441, doi:10.11676/qxxb2019.021
两类不同风灾个例超级单体特征对比分析
Comparative analysis of supercells associated with two different types of wind disaster
投稿时间:2018-04-23  修订日期:2018-10-12
DOI:10.11676/qxxb2019.021
中文关键词:  大风灾害  超级单体  龙卷  下击暴流
英文关键词:Disastrously convective wind  Supercell  Tornado  Downburst
基金项目:公益性行业(气象)科研项目(GYHY201506006)、国家科技支撑计划项目(2015BAC03B04)、国家重点研发计划项目(2017YFC1502003)。
作者单位E-mail
杨波 国家气象中心, 北京, 100081  
孙继松 中国气象科学研究院灾害天气国家重点实验室, 北京, 100081 sunjs_0314@sina.com 
刘鑫华 国家气象中心, 北京, 100081  
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中文摘要:
      采用分钟级加密自动气象站观测资料,盐城、淮安和岳阳、荆州雷达探测数据,以及欧洲中期天气预报中心(ECMWF)高分辨率的ERA-Interim全球再分析数据,对比分析了2016年6月23日江苏阜宁龙卷灾害和2015年6月1日湖北监利下击暴流大风灾害的环境特征与超级单体的结构特征。结果表明:(1)两次强对流大风灾害发生在相似的低空环流背景下:风灾发生在低空急流出口区左侧的暖区内、850 hPa低涡中心东侧6—7个经距的位置;环境大气的对流有效位能大于2000 J/kg。但是风灾的类型不同,江苏阜宁大风灾害主要由超级单体龙卷造成,监利“东方之星”沉船事故主要是超级单体触发的下击暴流造成。短时强降水中心与风灾中心的相对位置不同:阜宁龙卷移动方向的左侧伴随着最强短时降水;湖北监利沉船事件发生期间,风灾中心与短时强降水中心基本重合。鉴于不同性质的对流大风位置与超级单体母体的中心位置对应关系上存在差异,通过比较地面观测的瞬时大风与瞬时强降水中心的相对位置将有助于区分强对流大风的性质。(2)环境风垂直切变强度对对流风暴结构、发展、维持有重要影响:阜宁龙卷发生时,其上空0—6 km风垂直切变达4×10-3 s-1,超级单体有明显的向前倾斜结构,形成有界弱回波区;而监利强对流沉船位置0—6 km风垂直切变只有2.3×10-3 s-1左右,风暴单体中的上升气流近乎于垂直。阜宁超级单体中气旋,首先出现在0—1.5 km风垂直切变和0—3 km风暴相对螺旋度带状大值区,在向抬升凝结高度更低的环境移动过程中,其底部不断下降,形成龙卷;而在监利沉船区,中低层风切变和风暴相对螺旋度相对要弱得多,对应风暴单体中的中气旋强度、持续性较弱,中气旋底部高度维持在1.6 km左右。(3)环境湿度垂直结构特征不同可能是风暴单体形成不同类型灾害大风的重要环境因子。监利下击暴流造成的风灾发生时,在地面气温迅速下降过程中,气压变化呈现快速跳升又快速下降的“尖锥”形,气压峰值比降水峰值提前4 min出现。它与对流层中高层环境大气中较为深厚的干空气卷入对流风暴中造成水物质强烈蒸发、冷却过程有关。而阜宁风灾过程中,环境大气中层仅存在非常浅薄的干层,加之低层较为深厚的饱和大气环境,对应的地面冷池效应相对较弱。
英文摘要:
      Surface observations at minute-resolution from automatic weather stations, weather radar data from Yancheng, Huai'an, Yueyang and Jingzhou and the ECMWF ERA-Interim global high-resolution reanalysis data are used in this study. Characteristics of the circulation environment and structures of two supercells are comparatively analyzed. One supercell induced a tornado on 23 June 2016 and the other triggered a downburst on 1 June 2015. The results are as follows. (1) The two convective disasters occurred in similar circulation environments. The supercells with disastrous convective winds appeared to the east of the 850 hPa low vortex and in the warm zone to the left of the low-level jet. The distance between the center of the low vortex and the disaster area is about 600 to 700 km. In both cases, the convective available potential energy (CAPE) was higher than 2000 J/kg. However, features of the two wind disasters are different, i.e., the disaster in Funing was mainly caused by the tornado, and the accident of the "Eastern Star" on the Yangtze River was directly associated with the downburst. The relative position of maximum flash precipitation versus wind disaster is different in the two convective activities. The maximum flash heavy precipitation corresponding to the supercell center occurred on the left side of the moving direction of the tornado in Funing. The place where the ship capsized was coincident with the center of heavy precipitation during the severe convective weather. The position of the wind disaster relative to the instantaneous strong precipitation center is helpful for distinguishing downbursts from tornados caused by supercells. (2) The vertical wind shear of the environment has an important influence on the structure, development and maintenance of convective storm. The environmental vertical wind shear within 0-6 km reached 4×10-3 s-1 just before the occurrence of the tornado in Funing. The main body of the supercell tilted forward with height, corresponding to a strong inclined updraft and bounded weak echo region (BWER). However, the environmental vertical wind shear was only about 2.3×10-3 s-1 in Jianli, and the updraft of the storm cell was almost vertical. Before the tornado in Funing happened, the supercell with mesocyclone was first monitored in northwestern Jiangshu province, corresponding to the environment with strong vertical wind shear under 1.5 km and large storm relative helicity within 0-3 km. As the storm moved eastward with lower LCL (lifting condensation level), the bottom of the mesocyclone sank lower gradually, and the tornado formed finally. However, the 0-3 km relative storm helicity and 0-1.5 km vertical wind shear along the storm moving direction in Jianli were much weaker than that associated with the tornado in Funing. The bottom level of the mesocyclone in the storm was not lower than 1.6 km, and the storm intensity was weak with a short duration of mesocyclone maintenance. (3) The vertical structure characteristic of environmental humidity is an important factor to distinguish different types of disastrous convective wind. During the storm activity in Jianli, observations collected at automatic weather stations show that the pressure evolution exhibited a cone-shape with rapid jumping up and dropping down while temperature kept decreasing. The pressure peak appeared four minutes earlier than the precipitation peak appeared. It was associated with strong evaporation of hydrometers when the deep dry environmental air in the mid-troposphere was entrained in the convective storm. For the disaster in Funing, the ground cold pool effect was relatively weak, corresponding to a very shallow dry layer in the middle level and a deep saturated atmosphere in the lower level of the environmental atmosphere.
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