降雨对海洋动量通量的影响及数值模式实现

Rainfall is one of the important physical processes in water cycling and in maintaining energy balance between ocean and atmosphere. Previous studies always ignored mechanical energy input to ocean which produced by rainfall. However, the impact of rainfall on the air-sea momentum flux transport has rarely been mentioned. In this project, the parameterization of sea surface stress produced by rainfall, and the role of rainfall in the momentum flux transport between air and sea will be studied. Based on the current classical theory, Firstly, we will analyze the dependency of surface stress produced by rainfall on factors such as rain rate, sea surface wind speed, raindrop size distribution. Then, we will establish the three-dimensional dynamic model of raindrops. After that, modified parameterization of surface stress produced by rainfall will be proposed and imported to a coupled atmosphere-wave-ocean system developed by our group. With this coupled system, two group experiments would be designed to explore the role of rainfall in air-sea interaction. The first experiment will not consider the momentum flux induced by rainfall. The momentum flux induced by rainfall will add to the sea surface flux in the second experiment. Ocean response of these two experiments will be analyzed. According to analysis of experimental results, we can show how significance of momentum flux induced by rainfall compared to wind stress. Our research results are expected to provide useful suggestions and important contributions to other air-sea interaction research and operational ocean forecasting.

目前的海洋模拟中往往忽略降雨输入到海洋中的机械能，关于降雨对海洋动量通量的调整作用，还没有清晰的认识，因此当前的绝大多数业务化海洋数值模式中未考虑降雨对海洋的动量输送。本研究拟在前期的研究成果基础上，通过理论分析和诊断分析的方法，定量评估降雨致水平应力与降雨强度、海面风场、海面粗糙度和雨滴粒径分布等因素之间的动力关系，建立雨滴下落过程的三维动力数值模型，再现雨滴在大气湍流边界层内的运动情况，进而改进降雨致水平应力经验表达式，探讨合理的降雨致海洋动量通量调整的参数化方案。最后，借助区域大气-海浪-海流耦合数值模式，引入参数化方案，通过数值实验和实测数据的对比分析，研究海洋内部过程对降雨致海洋动量通量调整的响应。为其它海气相互作用研究奠定基础，同时也为实际业务化海洋预报与应用提供一定的参考和科学依据。

根据理论推导和分析，引入了降雨对海气界面动量通量影响的参数化方案；同时基于一定的假设，建立了降雨对海气界面热通量影响的参数化方案；在区域海气耦合模式的边界层中考虑了降雨参数化方案。对2013年超级台风“海燕”进行了数值模拟，发现同时考虑降雨和海洋飞沫和浪致混合等三种物理过程后提高了台风强度的模拟精度，风-压关系也有所改进。进一步模拟了2013年19个热带气旋的路径和强度模拟误差，将台风强度预报结果与中央气象台预报结果进行了对比，统计结果表明明显改进了强台风强度的预报精度.这一研究结果揭示了降雨和海浪等物理过程对台风强度预报的重要影响，为提高台风强度预报奠定了坚实科学基础，对台风研究和实际台风预报有重要的参考价值。