摘要
摘要:2017年6月22日广东西部经历了一次罕见的极端降水事件（24 h最大累积雨量562.5 mm），刷新了多项当地的历史雨量纪录。本文利用区域自动站、多普勒雷达和风廓线仪等观测资料，分析了这次极端暖区降水的维持机制，并通过二维雨滴谱仪、FY-3B微波湿度计研究了其微物理特征。结果表明：6月21日夜间一条地面中尺度辐合线触发对流单体，导致准静止长生命史MCS（Mesoscale Convective System）的产生和维持。这条辐合线位于天露山附近，处于由降水物蒸发冷却导致的较冷空气堆（较低相当位温）与来自海洋的较暖空气堆（较高相当位温）之间，中尺度辐合线两侧温差约2～3°C，环境大气的特征为对流抑制能量弱，抬升凝结高度低。本次降水事件中，对流云云顶高度较高，降水极值中心位于两个亮温极值中心之间过渡区以西的亮温梯度大值区，可降水量较高。降水雨滴谱在高湿环境中表现为暖性降水特征，最强降水时间段内，小雨滴数浓度超过10⁵ mm^?1 m^?3，远高于华南地区夏季平均值（约10⁴ mm^?1 m^?3），且同时存在部分大粒子，从而导致了更高的降水效率和局地强降水。MCS 产生的偏北风冷出流与西南暖湿气流相遇并产生强辐合，持续触发新的对流单体，使得MCS维持准静止，不断地产生降水。
关键词:极端降水/
暖区降水/
中尺度对流系统/
中尺度辐合线/
二维雨滴谱仪/
FY-3B微波湿度计
Abstract:A rare extreme precipitation event (maximum cumulative rainfall of 562.5 mm in 24 h) was experienced in western Guangdong on 22 June 2017, which resulted in a number of local historical rainfall records and caused serious property damage. This paper analyzed the maintenance mechanism of this extreme precipitation in the warm zone using the observation data of the automatic regional station and the Doppler radar and wind profiler. The microphysical characteristics of precipitation were studied using a two-dimensional video disdrometer (2DVD) and an FY-3D microwave humidity sensor. Results show that a surface mesoscale convergence line that triggered the convective cells on the night of 21 June leads to the generation and maintenance of the quasi-stationary long-life MCS (Mesoscale Convective System). The convergence line near the Tianlu Mountain lies between the cooler air reactor (lower equivalent potential temperature) caused by the evaporation and cooling of precipitation and the warmer air reactor (higher equivalent potential temperature) from the ocean. The temperature difference between the two sides of the mesoscale convergence line is about 2°C–3°C. The ambient atmosphere is characterized by the weak convection inhibition energy and low uplift condensation height. The height of the convective cloud on top of this precipitation event is relatively high, and the center of the extreme value of precipitation is located in the large value region of the bright temperature gradient that lies to the west of the transition zone between the two bright temperature extreme value centers. The precipitation raindrop spectrum shows the characteristics of warm precipitation in the high-humidity environment. During the period of the strongest precipitation, the concentration of small raindrops exceeds 10⁵ mm^?1 m^?3, which is much higher than the average value in south China during summer (about 10⁴ mm^?1 m^-3). Few large particles also exist, leading to a higher precipitation efficiency and local heavy precipitation. The cold outflow of the northerly wind generated by the MCS encounters the warm and wet airflow of southwest China and forms a strong convergence, which continuously triggers new convective cells, enabling the MCS to remain quasi-static and continuously produce precipitation.
Key words:Extreme precipitation/
Warm-sector precipitation/
MCS/
Mesoscale convergence line/
2DVD disdrometers/
FY-3B microwave humidity sensor



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