2021年6月东北冷涡暴雨水汽来源和源区贡献分析

Moisture Sources and Contributions of Source Regions to the Northeast Cold Vortex Rainstorm in June 2021

本文针对2021年6月2~3日发生在东北地区的冷涡暴雨过程,首先利用传统欧拉方法,初步分析了此次初夏东北冷涡暴雨过程的水汽输送与辐合特征,进而利用拉格朗日轨迹追踪模式FLEXPART和水汽来源与源区定量贡献分析方法,揭示出此次暴雨过程的水汽源地和源区定量贡献。结果表明:此次初夏冷涡暴雨过程期间,副热带高压偏南,东北地区主要受东北冷涡和其下游日本海弱高压脊影响,但对流层低层,副高主体与日本海弱高压脊之间存在气旋性切变流场,促成一支低空急流沿我国沿海地区北上,有利于东北地区南侧水汽向北输送,与东北冷涡后部干冷空气在辽宁和吉林省交汇,触发强降水。拉格朗日轨迹追踪显示,60%以上的目标气块来自降水区西侧和西北侧的亚欧大陆地区,这些气块初始位置高度较高,途径我国东海、黄海一带时,高度显著降低,并汇入偏南暖湿气流,进而流入目标降水区;还有部分气块来自贝加尔湖及其以东地区以及我国南海和中南部大陆地区,气块初始位置及行进过程中高度均较低。水汽源区对目标降水区的水汽定量贡献显示,东海—黄海至西北太平洋地区贡献最大(贡献率37.04%),中国大陆中东部紧随其后(贡献率30.05%),显著的水汽摄取和较低的沿途损失,使得上述两区域水汽贡献显著,而降水区局地摄取水汽的贡献排在第三位;此外,贝加尔湖及其以东地区和亚欧大陆中西部亦有一定贡献(尽管亚欧大陆中西部的水汽摄取总量亦较大,但绝大部分水汽在远距离输送过程中损耗),而印度半岛至中国南海地区水汽贡献最小。相对于传统的欧拉方法,拉格朗日方法可以更清晰地给出暴雨过程主要的水汽源地及其贡献。

In this paper,we first analyze the moisture transport and convergence characteristics of an early summer cold vortex rainstorm in Northeast China using the traditional Eulerian method.Subsequently,we use a Lagrangian particle dispersion model,FLEXPART,to quantify the contribution from various moisture sources.This helps us reveal the origins of moisture and their roles in this rainstorm process.The results show that during this early summer northeast cold vortex(NECV)rainstorm,the subtropical high pressure was positioned to the south.The northeast region was mainly influenced by the NECV and the weak high-pressure ridge in the Japan Sea downstream of it.In the lower troposphere,the cyclonic flow between the subtropical high and the weak high-pressure ridge in the Japan Sea contributed to a low-level jet northward along the coastal areas of China.This action was conducive to the northward transport of moisture from the southern part of Northeast China,which intersected with cold–dry airflow from the rear of the NECV in Liaoning and Jilin provinces,triggering heavy precipitation.Lagrangian trajectory tracking showed that>60%of the target air masses originated from the Eurasian continental region to the west and northwest of the precipitation area.These air masses started at a high elevation but significantly decreased in height as they passed through the East China Sea and the Yellow Sea,merging into the southward warm–wet airflow,which then flowed into the target precipitation area.The remaining air masses stemmed from Lake Baikal and its eastern region,as well as the South China Sea and the south–central continental region of China.These air masses maintained a relatively low height both at their origin and during transit.The quantitative contribution of moisture from the source regions to the target regions showed that the East China Sea–Yellow Sea to the Northwest Pacific made the largest contribution(37.04%),followed by East–Central China(30.05%).These regions demonstrated significant moisture uptake and low loss along the way,resulting in a substantial moisture contribution.The local precipitation area ranked third in moisture uptake.Lake Baikal and its eastern region,along with central–western Eurasia,also contributed,though most of the moisture from central–western Eurasia was lost during long-distance transport.The Indian peninsula to the South China Sea made the smallest moisture contribution.In conclusion,the Lagrangian method provided a clearer picture of the main sources of moisture and their contribution to the rainstorm process compared with the traditional Eulerian method.