多尺度复杂地形对华南暖区暴雨的影响机理及其数值预报效果改进研究

The heavy warm-sector rains over Southern China (HWRSC), characterized by its high frequency, strong intensity, are often associated with the favorable configuration between the complex orography and atmospheric circulation. Observation analysis shows that high and low frequency of the HWRSC highly matches with the complex orography, and often causes other secondary disasters (e.g., flood, debris flow). The mechanism and numerical studies on the multi-scale effect of complex orography on heavy warm-sector rains over Southern China, could bring important scientific value and application significance to improve the comprehension and prediction ability of HWRSC over the complex orography. . The high frequency satellite data, radar, meteorological observational data and monsoon field experiment data on heavy rainfall of SC will be used to study the effect of the orography to the MCSs (meso-scale convective systems) generation, development, evolution of structure, efficiency of raindrop formation and cloud microphysics, as well as the large scale and meso-scale effect of the Nanling mountains, Lianhua and Yunwu mountain, and the dynamic and thermal effects of the small-scale orography on the large-scale atmospheric circulation and MCSs. Mechanism analysis of heavy torrential rains caused by local orography including the small hills and trumpet-shaped topography will be discussed. This project will also analyze the effects of orography on the structure, dynamic and thermal configuration of the MCSs at different stage, as well as the correspondence precipitation distribution.. The lifting effect of orography on HWRSC, the blocking effect of orography on precipitation and the gravity wave effect induce by orography on momentum transport will be studied by using model simulation and diagnosis analysis. A scheme aiming at the parameterization of the rain enhancement of orography including the dynamic and thermal effects will be proposed to improve the forecasting of HWRSC based on observational analysis. The physics model of the effects of multi-scale orography on MCSs of HWRSC will also be summarized. With the study on the mechanism and numerical studies on the multi-scale effect of complex orography on heavy warm-sector rains over Southern China, could probably improve the level of diagnosis analysis and forecasting ability of meso-scale model.

引发山洪、泥石流等地质灾害暴雨的发生往往与复杂地形和大气环流场的有利配置密切相关。观测研究表明，华南几个多暴雨中心和少暴雨发生地区都与所处的独特地形有关，针对复杂地形对华南暖区暴雨的影响机理与数值预报改进效果的研究，对提高复杂地形下暖区暴雨的分析水平和预测能力具有重要的科学价值和现实意义。本项目拟开展复杂地形对暖区暴雨中尺度对流系统的发生、发展、演变结构、产雨效率和云微物理过程的影响，重点研究南岭山脉、莲花山、云雾山等共同构成的特殊大、中尺度地形效应、以及叠加在其上的小尺度地形的动力效应、热力作用及其日变化对华南暖区暴雨大尺度环境场及其中小尺度对流系统结构的影响，建立复杂地形下华南暖区暴雨天气系统发生发展的物理图像或物理概念模型，改进模式物理过程中对次网格地形的参数化方案，提高对华南暖区暴雨的模拟、预报能力和分析水平。

我国华南地处低纬度地区，地形复杂、暴雨频发，尤其是每年汛期期间，华南暖区暴雨强度大、降水集中，常造成局地山洪、滑坡与泥石流等地质灾害，是天气预报中的一个难点之一，研究地形效应对华南暖区暴雨的影响机理具有重要的现实意义。本项目组利用地面自动站资料、雷达和再分析资料，结合数值模拟，实施开展了地形对暖区暴雨影响的观测分析和数值模拟研究，分析了地形对暖区暴雨的触发和增强作用，统计分析了复杂地形下风和温度的日变化特征，并用数值模拟进行了对比验证，概括了多尺度地形对暖区暴雨影响的物理模型，提出了一种地面温度nudging方案，发展了一种次网格地形参数化方法。本研究结果有利于提高地形对暖区暴雨作用认识，发展的地面温度Nudging和次网格地形参数化方案，可有效提高GRAPES模式对暖区地面温度和风的预报能力。取得的主要结果有：. （1）分析地形对暖区暴雨的触发和维持作用。指出了地形对暖区对流的抬升触发作用，偏南气流和山区偏北气流形成中尺度对流边界，使得对流进一步增强，受东侧云开山脉的阻挡作用，使得对流增强维持，形成特大暴雨。. （2）分析了暖区暴雨风场变化与强对流的关系，指出强对流发生时，存在明显的南风和北风增强，其中南风增强时间与强对流出现时间较一致，最高峰出现在17-18UTC。强对流发生时，南北温差明显，独特的地理地形分布使得强对流在该地区该时间段频发。. （3）模式对对暖区特大暴雨过程预报量级明显偏低。分析发现，来自欧洲中心的初始场对华南暖区的地面温度描述偏低，导致GRAPES模式模拟的地面温度偏低。通过地面温度nudging可显著提高模式对地面温度的预报能力，降低模式对暖区地面温度预报偏低的现象。. （4）本研究提出了一种次网格地形参数化方案，增加了地形对地面风场的反馈的影响：在动量平衡方程中增加一动量沉积项，并在模式第一层中考虑此拖曳对风场的影响。结果表明，新方案可有效改进对近地层风的预报，显著降低了原模式中对低层风速的过高估计。.