华南沿海复杂地形和海陆下垫面耦合作用下强降水形成机理研究

Heavy rainfall events frequently occur over the coastal region of South China, which are difficult to predict and will result in severe disasters. Complex terrain and land-sea contrast are important influencing factors for the precise timing and location of heavy rainfall occurrences. Improving the understanding of the mechanism of heavy rainfall formation under the combined effects of terrain and land-sea contrast could help to improve the accuracy of precipitation forecast. Few studies have investigated the combined effects of terrain and land-sea contrast on the formation of heavy rainfall over the coastal region of South China. Therefore, in the present study, firstly, a detailed observational analysis of the heavy precipitation processes under the combined effects of complex terrain and land-sea contrast is performed using data from automatic weather stations, soundings, dual-polarization radar, wind profiler, and so on. High-resolution simulations are conducted to further reveal the effects of terrain and land-sea contrast on the formation of heavy rainfall through dynamic, thermodynamic and microphysical processes. A series of sensitivity experiments are designed and analyzed to isolate and quantify the impacts of terrain, land-sea contrast, and interaction between them. This study is aim at improving the scientific understanding of heavy rainfall over the coastal region of South China and providing useful information for practical forecast.

华南沿海地区强降水频发，预报困难，受灾严重。复杂地形和海陆下垫面影响着强降水的发生时间和落区。深入认识复杂地形和海陆下垫面耦合作用下强降水形成的机理对提高降水精细化预报水平和服务能力至关重要，但目前针对华南沿海地形和海陆下垫面共同影响强降水的研究尚不多见。本项目首先综合利用自动站、探空、双偏振雷达、风廓线等多源稠密观测资料，对华南沿海地形和海陆下垫面耦合作用下的强降水形成过程进行精细的观测分析，进而结合高分辨率数值模拟，设计敏感性试验，进一步揭示地形和海陆下垫面作用如何相结合，通过动力、热力和微物理过程影响强降水形成，区分阐明地形和海陆下垫面的不同影响以及两者相关的局地环流的相互作用对强降水形成的影响。项目研究成果可加深对华南沿海强降水形成机理的认识，为相关强降水预报提供重要参考依据。

华南沿海地区强降水频发，复杂地形和海陆下垫面特征影响着强降水发生的时间和地点。深入认识复杂地形和海陆下垫面耦合作用下强降水的形成机理对提高强降水预报水平和服务能力至关重要。本项目重点关注华南沿海地形区，同时也是强降水高发区，结合多源观测资料精细分析和高分辨率数值模拟试验，针对所选的阳江恩平沿海地形附近的强降水过程和惠州沿海地形附近的强降水过程的形成机理、地形和海陆下垫面在其中的作用开展了研究。.阳江恩平强降水过程由准静止的中尺度对流系统引发。前期，山地附近与陆风/下坡风相关的偏北风和沿岸盛行南风形成稳定辐合线，触发对流，进而组织发展成中尺度对流系统。同时沿岸地形附近触发对流，向东北移动。后期，冷池出流和偏南风的辐合使辐合线继续维持在阳江中部和天露山附近，对流系统和强降水得以维持。强降水主要由大量中小雨滴贡献，以对流性降水为主。通过敏感性试验揭示了不同位置地形和海陆下垫面差异对强降水的影响：沿岸地形抬升作用和绕流辐合有助对流触发；阳江中部地形和海陆下垫面粗糙度差异影响辐合线位置及其维持，地形同时阻挡雨带向北移动；天露山局部地形有助局地辐合及强降水的形成；地形和海陆下垫面粗糙度的相互作用使强降水落区偏南。.研究惠州破日雨量记录的强降水过程发现该过程低压系统较稳定地存在于中南半岛、北部湾地区，其影响下的向岸风对水汽输送有重要作用。定量分析得出水汽主要源区为阿拉伯海、孟加拉湾和中国南海。在逐渐西伸的高压脊影响下，局地风向风速的演变及其与西南-东北走向的莲花山脉地形的相互作用，加上高潭特殊地形附近的辐合，使得与山脉走向相近的雨带频繁在惠州高潭附近形成并维持，造成强降水。高潭强降水阶段霰粒子出现频率高，融化形成强降水，即淞附和融化过程有重要作用。.本项目成果有助加深对华南沿海强降水形成机理的认识，数值试验同时显示地形下垫面关键信息对局地辐合的模拟重现十分重要，为业务模式改进提供参考。