华南城市和海岸中小尺度天气的米级分辨率数值模拟与机制研究

High-precision fine-scale numerical weather prediction is essential for the disaster prevention and reduction. In particular, the improved understanding and predicting small scale severe weather phenomena at the cities and/or coasts is an important scientific issue and has valuable implications for the society. Over there, the complex conditions of buildings and topography strongly regulate the local variations of winds and temperature. The dynamical and thermal forcings of underlying surfaces also induce the activities of organized turbulent structures and local convection in the planetary boundary layer, which may further interact with mesoscale weather systems. To address these issues, we developed a full-scale nested local prediction system consisting of a regional data assimilation system and an urban scale building-resolving computational fluid dynamic model. Using this advanced prediction system, we propose to perform the super-high-resolution simulation over the mega cities and coastal areas of southern China for studying the local strong winds associated with typhoons, squall lines/fronts, and severe convective weathers. A series of analyses are conducted to reveal the detailed features variations of local weather with emphasis on the possible influence of tall buildings and local terrains. Further analyses are focus on the physical processes of buildings- or terrains-induced turbulent structures and their strong interaction with mesoscale weather system. Finally, the predictability of local weather at city streets is illustrated through examining the sensitiveness experiments on the changing weather conditions, underlying surface features, and numerical system configuration. With a better understanding of the local weather over complex surfaces, this study is warranted to provide new insights on the formation and forecast of the extreme disasters at cities and coastal areas.

发展精细化天气预报,特别是提升城市街道和海岸地形上的中小尺度天气的机制认识和预 报能力,具有重大科学意义和社会价值。建筑地形不仅能直接调节局地气流和温度分布,大型 城市的非均匀动力热力强迫还可激发有组织湍流和边界层对流,影响中小尺度天气系统活动。 本项目基于非静力气象模式、双向嵌套数据同化、云分辨率集合预报、计算流体动力模式、大 规模并行计算等先进技术,构建全尺度嵌套数值预报系统,针对影响华南城市和海岸的台风、 冷锋/飑线、强对流等进行米级分辨率的城市尺度数值模拟,深入探讨局地天气的精细特征、 物理机制和可预报性。研究内容主要包括:1)不同天气背景下,建筑和地形影响的局地天气三 维结构、演变过程和模拟验证;2)复杂下垫面上空的有组织湍流活动特征、规律机理及其与中 小尺度天气精细结构的多尺度相互作用机制;3)对大气条件、下垫面特征、扰动方案等开展敏 感性试验,评估关键因素影响局地天气变动的详细机理和可预报性。

发展精细化天气预报，特别是提升城市街道和海岸地形上的中小尺度天气的机制认识和预报能力，具有重大科学意义和社会价值。海岸地形和城市建筑不仅能直接调节局地气流和温度分布，还可激发有组织湍流和边界层对流，影响中小尺度天气系统活动。本项目针对影响华南城市和海岸的对流、台风等进行超高分辨率数值模拟，深入探讨局地天气的精细特征、物理机制和可预报性。研究内容包括：(1)建筑和地形影响的局地天气三维结构、演变过程和模拟验证；2)局地扰动活动特征、规律机理及其与中小尺度天气精细结构的多尺度相互作用机制；3)评估大气条件、下垫面特征等因素影响局地天气变动的机理和可预报性。.项目研究已在海风锋面三维结构、对流触发观测、对流多尺度机制、暖区暴雨成因、热带气旋中的强对流系统等多个层面取得了具有重要科学意义的一系列研究成果，提升对海岸和城市等复杂下垫面上空的局地天气的科学认识。重要结果包括：（1）成功实现实际海风锋面三维结构的世界首例超高精度数值模拟，揭示小尺度湍流与锋面结构的相互作用、建筑物影响等机制；（2）基于高分辨率的雷达观测资料，建立了首个多年高时空分辨率的华南对流触发数据集，揭示了季风海岸对流触发的精细时空分布和变化规律；（3）基于高分辨率的数值模拟和敏感性试验，揭示海岸地形和岛屿的对流触发的多尺度机制；（4）基于云分辨率模拟试验和集合预报分析，研究华南海岸暖区暴雨的多尺度变化机制，提出了双低空急流的新概念模型；（5）研究了热带气旋中的强对流系统（龙卷、深厚对流），揭示它们与环境条件的紧密联系。项目资助发表了17篇论文，大多数发表在大气科学领域的顶尖期刊，多个关键成果入选期刊封面或ESI高被引论文。