Spatiotemporal Evolution Characteristics and Causes of Short-Duration Heavy Rainfall in the Presummer Rainy Season over the Pearl River Delta Region Before and After the South China Sea Summer Monsoon Onset in the Past 20 Years
Spatiotemporal Evolution Characteristics and Causes of Short-Duration Heavy Rainfall in the Presummer Rainy Season over the Pearl River Delta Region Before and After the South China Sea Summer Monsoon Onset in the Past 20 Years
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江三角洲地区(简称珠三角)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,但短时强降水频率在季风爆发后增加70％.(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.短时强降水频率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16％.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.
Abstract
Compared to daily-scale heavy rainfall,short-duration heavy rainfall(≥20 mm h-1)is responsible for mountainous region torrents,mudslides,and urban waterlogging.Using automatic meteorological stations and ERA5 reanalysis data,this study focuses on the temporal and spatial characteristics of short-duration heavy rainfall over the Pearl River Delta region before and after the onset of the South China Sea summer monsoon and explores the possible causes of the differences of short-duration heavy rainfall before and after the monsoon onset.Results show that(1)compared to that before the monsoon onset,the precipitation over the Pearl River Delta region after the monsoon onset increased,owing to the short-duration heavy rainfall frequently occurred.Regional mean intensity and extremes of the short-duration heavy rainfall were comparable during the stages before and after the monsoon onset,but the frequency of short-duration heavy rainfall increased by 70％after the monsoon onset.(2)Short-duration heavy rainfall mainly occurred in the northeastern and southwestern parts of the Pearl River Delta region.The frequency of short-duration heavy rainfall in the two abovementioned areas significantly increased after the monsoon onset,and exhibited a double peak(i.e.,in the morning and afternoon)versus a single peak(i.e.,in the afternoon)before the monsoon onset.(3)The occurrence of short-duration heavy rainfall varied over the Pearl River Delta region.The mean intensity and extremes of short-duration heavy rainfall after the monsoon onset were higher insouthwestern parts of the Pearl River Delta region than in inland areas.The frequency peaked in the afternoon before the monsoon onset while in the morning after the monsoon onset along the coast.However,the frequency consistently peaked in the afternoon in inland areas.(4)After the monsoon onset,the low-level moisture content during the short-duration heavy rainfall period increased by 16％compared to the climatology.Abundant water vapor was transported to the coast supported by the nocturnal acceleration of the monsoonal flow,confronting the land breeze,which enhanced the low-level convergence.(5)The frequency of short-duration heavy rainfall was closely related to the magnitude of the low-level water vapor flux after the monsoon onset.The increased short-duration heavy rainfall in the midnight and early morning in the coastal areas was associated with the dynamic forcing in the middle and low levels.However,the short-duration heavy rainfall in inland areas was attributed to thermal conditions and unstable atmosphere.These results help to understand the characteristics and formation mechanism of the short-duration heavy rainfall over the Pearl River Delta region.
关键词
短时强降水/珠三角地区/季风爆发前后/时空分布/可能成因
Key words
Short-duration heavy rainfall/The Pearl River Delta region/Before and after monsoon onset/Temporal and spatial distribution/Possible cause
维普
万方数据