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ISSN 1006-9895

CN 11-1768/O4

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2018年8月华南超历史极值降水事件的观测分析与机理研究
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作者单位:

1.成都信息工程大学;2.国家气象中心

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基金项目:

41175048


A Record-breaking Heavy Rainfall Event over Southern China During August 2018: Analysis of Observation and Mechanism
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National Meteorological Center

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    摘要:

    2018年8月30~31日一条超长生命期的中尺度线状对流(线状β-MCS)引发了华南沿海一次极端降水事件(24小时雨量1056.7mm),刷新广东省日雨量历史纪录,造成严重洪涝并引起社会极大关注。文章利用多源观测资料与NCEP/NCAR_FNL再分析资料,首先从观测分析角度提炼该次过程的降水特点、与卫星、雷达的基本演变特征,然后分析了极端降水的天气尺度背景与中尺度环境条件,最后从中尺度大气动力学角度探讨超长生命期线状β-MCS的触发演变与海陆边界风向旋转维持的关系,并揭示线状对流组织与维持的可能物理机制。结果表明:季风低压作为稳定的天气尺度背景,大气层结表现为深厚暖湿与持续不稳定,季风云团北推上岸造成华南沿海大范围暴雨,一条超长生命期、准静止、后向传播、低顶高、低质心的线状β-MCS造成高潭持续性强降雨,降水强度大、持续时间极长是累积雨量破纪录的主要原因。对流触发及线状β-MCS组织发展过程与地面风场有密切关系,利用海陆边界风向旋转率方程定性分析发现地面风场受多尺度调节影响,季风低压的天气尺度项、局地地形摩擦项共同强迫风向逆转变化,与中尺度气压梯度项强迫风向顺转变化达到平衡,造成地面偏南风长时间维持。斜坡地形与黄江河谷一侧偏南风增强并建立“暖脊”,致使山脉一侧冷池出流边界无法向南扩展,形成强烈的水平温度梯度,基于中尺度动力学方程定量诊断表明β-MCS的线状组织过程及对流维持的动力机制来源于局地垂直风切变,这种局地垂直风切变有别于环境风垂直风切变,其显著增强是对地面局地强烈水平温度梯度响应的结果。

    Abstract:

    An extreme daily rainfall (maximum of 1056.7mm) induced by a long-lived linear-shaped mesoscale convective system (β-MCS) occurred over Gaotan town (GT) of Guangdong province during 30-31 August 2018, which broke the historical record in Guangdong province, caused severe flash flood and aroused social concern. Based on multiple observation data and NCEP/NCER_FNL reanalysis, we performed properties of the precipitation, convective systems evolution, synoptic and meso scale environmental conditions, initiation and maintenance of the β-MCS. It is shown that tropical cloud clusters move northward and induce large-scale heavy rainfall, with background of monsoon depression as well as mesoscale favorable environment of high-thermal, high-humidity. Extreme rainfall over GT is caused by a linear-shaped β-MCS, characterized by back-building, over-long-lived, quasi-stationary, low echo-top-height and low echo-convective-centroid. Organization of β-MCS is closely related to near-surface wind field, which is affected by multi-scale systems that we qualitatively analyze using rotation rate equation of sea and land breezes. The southerly flow is able to sustain for a long period that is determined by the forcing of multiple interaction, that monsoon depression and local terrain induce southerly flow to rotate counterclockwise, but barometric gradient induces southerly flow rotate clockwise, and take a balance finally. Southerly flow on the side of river valley HJ over slope terrain strengthening helps the warm-ridge development of temperature field, blocking cold pool outflow boundary move southeastward on the side of mountain over slope terrain, leading to sharp temperature gradient over that region. Quantitative diagnosis using mesoscale atmospheric dynamics equation shows the dynamic mechanism to sustain convection maintenance and β-MCS organization stems from local vertical wind shear, causing by the sharp temperature gradient.

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  • 收稿日期:2018-12-10
  • 最后修改日期:2019-04-24
  • 录用日期:2019-08-19
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