罗琪,郑永光,陈敏. 2019. 2017年北京北部一次罕见强弓状飑线过程演变和机理[J]. 气象学报, (0):-, doi:10.11676/qxxb2019.026
2017年北京北部一次罕见强弓状飑线过程演变和机理
Evolution and development mechanisms of a rare strong arc-shaped squall line occurring in Northern Beijing in 2017
投稿时间:2018-07-16  修订日期:2018-09-30
DOI:10.11676/qxxb2019.026
中文关键词:  弓状回波,飑线,超级单体,演变,机理
英文关键词:Bow echo, Squall line, Supercell, Evolution, Mechanism
基金项目:国家重点研发计划(2017YFC1502003), 国家自然科学基金项目(41375051)
作者单位E-mail
罗琪 中国气象科学研究院北京 loco420@163.com 
郑永光 国家气象中心北京 zhengyg@cma.gov.cn 
陈敏 中国气象局北京城市气象研究所北京 mchen@ium.cn 
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中文摘要:
      2017年7月7日下午至午夜,河北西北部和北京中北部发生了一次罕见的最大瞬时风力将近12级并伴有大冰雹的强弓状飑线过程,其触发、演变和维持机制等具有较高研究价值。综合多种观测资料和 NCEP分析资料,本文利用“配料法”分析了该次飑线过程的环境条件、触发、演变、风暴结构和弓形回波的形成与维持机制。飑线发生在500 hPa冷涡西南部的前倾槽和低空急流形势下;超过2000 J/kg 的对流有效位能(CAPE)、强0–6 km和0–3 km垂直风切变为弓状飑线及其相关超级单体的生成和维持、大冰雹和地面强风的形成提供了有利条件;较低的湿球温度0 ?C层(~3.8 km)是有利于大冰雹形成的融化层高度;对流层中层高达30 ?C温度露点差与大的垂直减温率造成环境大气具有强的下沉对流有效位能(DCAPE),利于弓状回波和地面大风形成。初始对流形成于西北风和西南偏西风之间的地面辐合线附近。地面大风和冰雹主要分布于低TBB和以正闪为主的闪电活跃处。雷达回波显示飑线先由线状对流系统发展成为团状超级单体对流系统,最后演变成弓状飑线。超级单体阶段和飑线阶段都有明显的回波悬垂、弱回波区、中气旋(飑线成熟后期为中涡旋)、强后侧入流及其伴随的入流缺口等;对流层中层急流和大的温度露点差是形成强下沉气流并发展出弓状特征的主要原因;大的CAPE和DCAPE值以及强垂直风切变是飑线维持的原因。
英文摘要:
      Based on NCEP (National Centers of Environmental Prediction) analyses data and various observations from automatic weather stations, cloud-to-ground lightning positioning system, stationary meteorological satellites, and weather radars, this paper uses "ingredient-based method" to have comprehensively analyzed environmental conditions, evolution characteristics, trigger and development mechanisms of a rare strong arc-shaped squall line with maximum instantaneous wind of nearly F12 and large hail, which swept the northwestern Hebei Province and central and northern Beijing during the period from afternoon to midnight of 7 July, 2017. The squall line occurred in the southwest side of a 500-hPa cold vortex. Strong low-level jet, larger convective available potential energy (CAPE) above 2000 J/kg, intense 0–6 km and 0–3 km vertical wind shear were very favorable for the development and maintenance of the squall line and a supercell storm embedded in the squall line, which produced large hail and high winds. Level of the wet bulb temperature 0 ℃ at 3.8 km altitude was in favor of producing large hail. Dewpoint deficit of the middle troposphere up to 30 ℃ and larger vertical temperature lapse rate caused larger downdraft convective available potential energy (DCAPE), which favored very much bow echoes and high winds. The convection initiation of the squall line was triggered near a surface convergence line between northwesterly winds and southwesterly winds. High winds and large hail were mainly located in the low TBB and active positive cloud-ground lightning area. Radar observations show that the squall line developed from a linear convection system to a cluster supercell storm, and finally to an arc-shaped squall line with significant overhang echoes, weak echo regions, mesocyclone (or mesovortex), and strong rear inflows which caused rear inflow notches. Intense downdraft induced by strong jet in the middle of troposphere and high dewpoint deficit was the main cause for the formation of the bow echoes in the squall line. The mechanisms of maintaining the squall line and bow echoes include: large CAPE and DCAPE, and intense vertical wind shear.
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