双月刊

ISSN 1006-9895

CN 11-1768/O4

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北京地区一次飑线的组织化过程及热动力结构特征
作者:
作者单位:

1.北京市气象台;2.中国气象科学研究院灾害天气国家重点实验室;3.北京城市气象研究院

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基金项目:

国家自然基金(41575050),公益性行业(气象)科研专项(GYHY201506006),中央级公益性科研院所专项基金项目(UMKY201606)


The Organization Process and Thermal Dynamic Structure of a Squall Line in Beijing
Author:
Affiliation:

1.State Key Laboratory of severe weather, Chinese Academy of Meteorology Sciences;2.Institute of Urban Meteorology, CMA

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    摘要:

    2015年8月7日华北西北部的一次断线状对流系统向东南方向移动并与平原地区多单体雷暴合并、组织,最终形成强飑线的过程,造成北京地区出现较大范围的风雹和局地短时强降水天气。基于多源资料的研究结果表明:(1)飑线形成有三个阶段:上游线状对流发展移动、平原多个单体雷暴的新生和合并、线状对流并入本地多单体后组织成飑线。第二阶段中,城区边缘地面热力分布不均,配合局地风场辐合,触发了雷暴,出现对流冷池后,热力不均的范围扩大,温度梯度区向南发展,造成新生对流向南传播。(2)飑线的组织化过程,呈现出两支强入流为典型特征的动力学结构:一支入流位于飑线后侧中层(4500-5000m),另一支为冷池前侧低层、垂直于飑线的强入流,这两支入流分别构成飑线前侧和后侧两个独立的顺时针垂直环流圈。后侧入流和前侧入流的同时加强,造成飑线前侧垂直环流不断强化,与之对应的垂直风切变也同步增强,这一动力学过程形成了有利于飑线组织化的中尺度垂直切变环境,同时也是驱动飑线快速向前移动和发展的重要因素。当后侧中层入流消失,前侧垂直环流也逐渐减弱,预示着飑线从成熟开始减弱消亡。(3)从热力学结构看,下山的线状对流与平原地区多单体雷暴的冷池合并,形成了扰动温度低于-8℃、厚度加深到1.5km的强冷池,其前沿的β中尺度锋面附近的辐合上升运动加强,进一步促进了平原地区的飑线发展加强,并出现阵风锋。

    Abstract:

    A broken line convective system, appeared in the northwest of North China, moved to southeast and collided with multi-cells in the plain of Beijing, and eventually formed an organizational strong squall line. It caused local flash rain, gust and big hail over Beijing on Aug. 7, 2015. Based on multiple sources data, the analyzes indicated that, (1) the squall line formation process had three stages: The developing and moving of broken line convective system in the upstream, the rebirth and consolidation of multiple cells in the plain and the organization of the squall line after the upstream broken line convective system crossed over mountains and merged into multi-cells in plain. During the second stage, the local convection was triggered near the urban city by the inhomogeneous temperature distribution together with local convergence;Corresponding with the cold pool, the reborn convection propagated toward south because of the enlarging scale of the inhomogeneous temperature and the southward intensified temperature gradient; (2) At the squall-line development stage, dynamic structure is characterized by two strong inflows. The mid-tropospheric rear inflow was at 4500 to 5000m height, another was the low-level strong inflow perpendicular to squall-line orientation. The two inflows induced two separated vertical clockwise circles at the former and behind the squall line. The vertical circulation in the front of squall line was intensified continuously since the rear and front inflows enhanced together, corresponding with strengthening vertical wind shear. This dynamical process induced the advantageous ambient mesoscale vertical shear for the squall-line organization, which also was a significant factor for the squall-line rapid movement and development. After the rear inflow disappeared, the frontal vertical circulation weakened and squall line dispersed gradually; (3) for the thermodynamic structure, a stronger cold pool appeared with the disturbance temperature -8℃, depth 1.5km, when the upstream convection system merged into the multi-cells system in the plain. As a result, upward motion was strengthened in the leading edge of the β-mesoscale temperature gradient. It was favor to squall line intensifying and developing and induce gust front.

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  • 收稿日期:2019-08-05
  • 最后修改日期:2020-04-20
  • 录用日期:2020-07-16
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