副高边缘辽宁短时强降水过程的水汽特征分析

Analysis of water vapor during short-time heavy rainfall events at the edge of subtropical high in Liaoning Province

西太平洋副热带高压(简称副高)边缘的短时强降水突发性强、降水集中、可预报性低,常常给预报带来挑战。筛选出2021—2022年5—10月发生在副高边缘的辽宁8次区域性短时强降水过程,基于副高及西风带影响系统将上述强降水过程分为副高边缘低槽和副高边缘涡旋两类。利用常规气象观测资料、ERA5再分析资料和GDAS气象数据,应用HYSPLIT4轨迹模式,重点分析上述两类短时强降水过程中的水汽输送特征,并分别挑选其中强降水覆盖范围大且出现短时强降水站数最多的一次过程作为典型短时强降水个例分析水汽通量变化和低空急流的作用。结果表明,受副高和低涡、高空槽的共同影响,辽宁上空水汽多来自于欧亚大陆中部、我国东部沿海、内蒙古和华北地区。尽管受相似的天气系统影响,不同天气过程的水汽输送通道仍表现出明显差异,对应为气团的源地、移动轨迹和气团获得水汽的途径不同。水汽通量大值区的演变与850hPa风场的演变趋势一致。短时强降水过程中,在低空急流的动力抬升和水汽输送作用下,水汽辐合大值区、强上升气流区和水汽输送通道三者的位置均与低空急流所处的位置密切相关。辽宁副高边缘典型短时强降水过程中,来自欧亚大陆中部和内蒙古地区的气团在水汽供应方面占比约为32%。

The short-time severe rainfall at the edge of the western Pacific subtropical high(referred to as the Subtropical High)is characterized by strong bursts,concentrated precipitation,and low predictability,often posing challenges for forecasting.Eight regional short-time severe rainfall events at the edge of subtropical high in Liaoning from May to October during 2021 and 2022 were examined.The synoptic situations of these events are divided into two categories according to the synoptic systems that cooperate with the subtropical high,which are the low trough at the edge of the subtropical high and the vortex at the edge of the subtropical high.Based on the European Center for Medium-Range Weather Forecasts(ECMWF)ERA5 reanalysis data,NCAR/NCEP GDAS data,conventional observation data,and HYSPLT4 model,the variation characteristics of the water vapor transport of the short-time heavy rainfall events during these two categories are studied.The changes in water vapor flux and the role of low-level jets were analyzed by investigating typical rainfall cases with the largest coverage of heavy precipitation and the most number of short-term heavy precipitation stations.The results are as follows.Under the upper-level trough and the cold vortex at the edge of the subtropical high,the water vapor over Liaoning mainly comes from the Central Eurasian continent,the eastern coast of China,the Inner Mongolian area,and North China.Despite the influence of similar synoptic systems,the water vapor transport pathways are significantly different,corresponding to differences in air mass sources,movement trajectories,and the way air mass obtains water vapor.The evolution of the high-value area of water vapor flux is consistent with the variation of the wind field at 850 hPa.During short-time heavy rainfall events,under the situation of low-level jet uplift and water vapor transport,the positions of the high-value area of water vapor convergence,strong updraft area,and water vapor transport pathways are closely related to the position of the low-level jet.The air mass from the Central Eurasian continent and the Inner Mongolian area contribute to 32% of the water vapor supply during the short-time severe rainfall events at the edge of the subtropical high in Liaoning.