陕西一类“东高西低型”暴雨的基本特征

The Features of a Type of West-Low and East-high Heavy Rainfall in Shaanxi Province

以NCEP再分析资料作为WRF模式初始场,加入常规观测资料、西安理工大学小型地面气象站观测资料和激光雷达雨前探测资料,对2015年4月初发生在陕西南部的一次暴雨过程(记为1504强降雨)开展高分辨中尺度模拟。在确保模拟资料质量可靠基础上,对模拟资料与观测资料开展综合诊断分析,研究了1504强降雨的基本特征。结果表明,这是一类"东高西低"型降雨过程,青藏高原东侧的暖低压与华北地区的冷高压共同导致暖湿气流与干冷空气在陕西南部交汇。饱和的大气是强降雨发生的有利条件(水汽含量达10.3 g·kg-1),而风速切变导致了强降雨的爆发,在此过程中诸要素与强降雨之间呈现出谷、峰相配的密切关联。"东高西低"形势的形成过程,体现的是降雨中心四周气压同时降低的特征,而非东部气压升高、西部气压降低的特征。在整个降压的过程中,西部气压降得更低、东部气压相对较高,由此构成"东高西低"的有利形势。最终,归纳了陕西这类"东高西低"型强降雨发生的概念模型。

By using the Multiquadric method and the WRFDA（ WRF data assimilation system） module,various data including the temperature data detected from the Raman Lidar in XAUT（ Xi＇an University of Technology）,the mini-meteorological station observation data in XAUT and the convectional observation data were integrated into the initial field of WRF（ Weather Research and Forecasting model）. And a high resolution numerical simulation on a heavy rainfall case occurred in Shaanxi province in April 2015 was carried out. The quality control on the simulation data was conducted by using the quantitative check method and qualitative check method,and the results show ed that the model had well copied the heavy rainfall case. Based on the simulation data and observation data,a new method named synthetically analysis and classifying diagnosis technique was used to study the features and formation process of the heavy rainfall case. It was a type of west-low and east-high rainfall. The warm low in the east of Qinghai-Tibetan Plateau and the cold high in North China together caused the collision betw een the warm-w et air and the cold-dry air in south Shaanxi. The air was near to be saturated with a water vapor mixing ratio of 10. 3 g ·kg-1,which was favorable of the rainfall,and the shear of wind speed triggered the heavy rainfall. Also,the features of the weather type of west-low and east-high,and the formation of the low and the high system were introduced respectively. The low located to the west of Shaanxi was closely related to the Qinghai-Tibetan Plateau. The air flow ed over the Plateau and formed the weather type of the low-pressure to the east of the Plateau. On the other side,the high located to the east of Shaanxi was from the middle part of Inner Mongolia. The Mongolia High would move southeasterly to Hebei province and Beijing,and it would couple with the ridge of high pressure over the Eastern China. Thus,the weather type of the east-high was formed. Generally speaking,it was the closed high and closed low that together caused the heavy rainfall. In fact,the typical characteristic of the west-low and east-high was that the pressure around the rainfall center reduced together,instead of a situation of reducing-pressure in west part and increasing-pressure in east part. During the reducing-pressure process,the east station possessed a higher pressure than the west station. In the end,a type of conceptual model for the heavy rainfall in Shaanxi province was proposed according to this study.