两类低空急流对华南前汛期暴雨的影响机制

前汛期华南暴雨频发且预报难度大，低空急流是造成暴雨的重要因素。研究低空急流对暴雨发生发展的影响机制，具有重大科学意义和社会价值。近期研究表明华南存在两类低空急流：边界层急流和与天气系统相关的低空急流，它们具有不同的时空特征和形成原因。目前，这两类急流分别影响华南暴雨的机理尚不清楚，有待深入研究。本项目从区分两类低空急流的新视角出发，基于高分辨率观测数据和数值模式，利用统计分析、动力诊断、集合预报等手段，深入探讨两类急流的精细结构及其对华南暴雨的影响，进一步阐明相关的对流发展机制和关键因素。主要内容包括：1）从统计角度，研究两类急流与降水在空间分布和日变化等方面的对应关系；2）基于云分辨数值模式，研究两类急流的时空配置及其与海陆、地形、冷池等下垫面强迫、锋面系统和重力波的相互作用，揭示它们对暴雨相关的强对流触发和维持的贡献；3）通过集合预报，分析低空急流影响暴雨预报的敏感性及关键因子。

Heavy rainfall often occurs in South China during the pre-summer rainy season and is hard to predict. Low-level jet (LLJ) is one of the most important factors on the heavy rainfall. It is of great scientific significance and social value to study the impact of the LLJ on the occurrence and development of heavy rainfall in South China and the underlying mechanisms. Recent studies have indicated that LLJs could be classified into two types: a boundary layer jet and a synoptic-weather-related LLJ, which exhibit different characteristics and formation mechanisms. The effects of the two types of LLJ on heavy rainfall have not been well understood until now, and need to be further studied. The innovative perspective of this project is the distinction between two types of LLJs. Based on the intensive observations and numerical simulations, the project will explore the fine structure of the two types of LLJ and their impacts on the distribution of heavy rainfall in South China, and further clarify the relevant formation and development mechanisms of heavy rainfall by statistical analysis, dynamic diagnosis and ensemble forecasting. The main research contents include: 1) the relationship between the two types of LLJs and precipitation in spatial distribution and diurnal variation, 2) the interactions between LLJ and terrain, cold pool, frontal systems and gravity waves, and their contributions to the triggering and maintaining of severe convection, 3) the forecasting sensitivities of heavy rainfall on LLJs, and associated key factors.