1.School of Atmospheric Sciences, Sun Yat-Sen University/Guangdong Province Key Laboratory for Climate Change and Natural Disaster Studies/Key Laboratory of Tropical Atmosphere-Ocean System;2.Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai);3.National Observation and Research Station of Coastal Ecological Environments in Macao, Macao Environmental Research Institute, Macau University of Science and Technology
相较于暴雨这种日尺度强降水，短时强降水（≥20 mm h-1）是造成山洪滑坡与城市内涝等灾害更为直接的因素。本文利用地面气象观测站和ERA5再分析数据，重点研究南海季风爆发前后珠三角地区短时强降水的时空演变特征，并探索了短时强降水在季风爆发前后特征与差异的可能成因。研究表明：（1）相较于季风爆发前，珠三角地区季风爆发后的降水明显增多，其中短时强降水贡献的比例显著增加。对短时强降水本身而言，区域平均强度以及极端性在季风爆发前后差异总体较小，但短时强降水频次在季风爆发后增加70.0%。（2）短时强降水高发区主要集中在珠三角东北部和珠江口西侧沿海，季风爆发后上述两个地区的频次增多最明显。短时强降水频次由季风爆发前的单峰型（下午）转为季风爆发后的双峰型（早晨与下午）。（3）短时强降水具有明显的区域性变化特征，短时强降水在季风爆发后的平均雨强和极端性在珠江口西侧沿海较内陆地区明显增强，其频次峰值时间在沿海地区从季风爆发前的午后转为季风爆发后的早晨，内陆地区在季风爆发前后均集中在下午。（4）季风爆发后，短时强降水期间的低层环境水汽超过同期气候态水平的15.6%。充沛的水汽在夜间在季风加速作用下被输送至沿海，并与陆风作用增强了辐合，这解释了沿海短时强降水的在季风爆发前后频次峰值时间转换现象。（5）相较于季风爆发前，季风爆发后珠三角短时强降水频率与低层水汽通量的相关性明显升高。珠三角沿海地区夜间-早晨短时强降水的增多与中低层风场结构改变造成的动力强迫有关。内陆地区季风爆发前后短时强降水与环境热力和不稳定条件关系更大。这些结果有助于我们更好地了解珠三角地区在季风爆发前后短时强降水的时空分布特征和理解其产生机制。
Compared with heavy rainfall on daily scale such as torrential rain, short-duration heavy rainfall (≥20 mm h-1) is a more direct cause of disasters such as mountain torrents, mudslides and urban water logging.Using ground automatic meteorological stations and ERA5 reanalysis data, this study focuses on the temporal and spatial evolution characteristics of short-duration heavy rainfall over the Pearl River Delta region before and after the onset of South China Sea summer monsoon, and explores the possible causes of the characteristics and differences of short-duration heavy rainfall before and after the monsoon onset. Results show that: (1) Compared to those before the monsoon onset, the precipitation over the Pearl River Delta region after the monsoon onset has increased significantly, and the contribution of short-duration heavy rainfall has increased significantly. For the short-duration heavy rainfall itself, the regional average intensity and extremes have little difference before and after the monsoon onset, but the frequency of short-duration heavy rainfall increases by 70.0% after the monsoon onset. (2) The high incidence areas of short-duration heavy rainfall are mainly concentrated in the northeastern part of the Pearl River Delta region and the west coast of the Pearl River Estuary. After the monsoon onset, the frequency of the above-mentioned two areas increased most obviously. The frequency of short-duration heavy rainfall changed from single peak (afternoon) before the monsoon onset to double peak (morning and afternoon) after the monsoon onset. (3) Short-duration heavy rainfall has obvious regional variation characteristics. The average rainfall intensity and extremes of short-duration heavy rainfall after the monsoon onset are significantly stronger in the west coast of the Pearl River Estuary than in inland areas, the frequency peak time in coastal areas changes from the afternoon before the monsoon onset to the morning after the monsoon onset, inland areas are concentrated in the afternoon before and after the monsoon onset. (4) After the monsoon onset, the low-level water vapor during the short-duration heavy rainfall period exceeded 15.6% of the climate mean. Abundant water vapor is transported to the coast under the nocturnal acceleration of the monsoon, and combine with the land breeze to enhance the convergence, which explains the frequency peak time conversion of the short-duration heavy rainfall in the coastal area before and after the monsoon onset. (5) Compared to those before the monsoon onset, the correlation between the frequency of short-duration heavy rainfall and the low-level water vapor flux in the Pearl River Delta region increased significantly after the monsoon onset. The increase of night-morning short-duration heavy rainfall in the coastal areas of the Pearl River Delta region is related to the dynamic forcing caused by the structural change of the wind field in the middle and low layers. The short-duration heavy rainfall before and after the monsoon onset in inland areas is more closely related to the environmental thermal and unstable conditions.These results advance our understanding of the temporal and spatial distribution characteristics of short-duration heavy rainfall before and after the monsoon onset over the Pearl River Delta region and its generation mechanism.