复杂地形边界层中尺度气象与大涡模拟耦合模式研究

Many scholars have done a lot of theoretical research on atmospheric boundary layer based on large-eddy-simulation (LES) and have made great achievements. However, most studies are focused on idealized cases rather than real cases. With the growing requirement of theoretical study and application of the refined numerical forecast, it is critically needed to develop LES for atmospheric boundary layer simulation in real cases, especially over complex terrain area. The refined simulation of atmospheric boundary layer over complex terrain has great significance in the fields of high impact weather forecast, atmospheric pollution dispersion, wind energy development and so on. In this program, LES will be coupled with mesoscale model, and the coupled model will be used to simulate temperature field and velocity field in boundary layer over complex terrain. Multiple nested method is employed for dynamical downscaling. The grid spacing is downscaling from the outermost mesoscale domain to the finest microscale domain. The high-precision elevation digital data are imported, and the high-resolution grids are established. After optimizing and improving the parameterization scheme combination, the simulation results will be analyzed, evaluated against corresponding experimental data. Then the main factors affecting the simulation performance of the coupled model in complex terrain conditions are analyzed deeply. On this basis, we will obtain turbulent velocity fluctuations and gust disturbance from simulated velocity field，and the typical characteristics of refined structures are extracted and studied. This study has great practical value for the development of LES of boundary layer and refined numerical weather prediction. Meanwhile, it will provide the basis for the establishment of boundary layer theory over complex terrain.

国内外已有许多基于大涡模拟(LES)的大气边界层研究，并取得了丰硕成果。但大多研究主要集中在理想条件，对真实情况的模拟研究还很缺乏。随着近年来对精细化数值预报的理论研究和业务需求越来越高，改进和发展可用于真实复杂地形大气高分辨模拟的LES显得越发迫切。复杂地形边界层精细化模拟对高影响天气预报，大气污染扩散，风能开发等领域都有着重要意义。本项目拟将中尺度气象模式与LES相耦合，采用多重嵌套逐步动力降尺度法，导入高精度地形高程数据，生成精细计算网格，开展复杂地形边界层高分辨率模拟试验。结合针对复杂地形的综合观测，检验、评估耦合模式在复杂地形下的模拟性能，深入分析主要影响因素。在模拟基础上，获得湍流脉动、阵风扰动等大气运动数据，从中提取并研究小尺度运动精细结构的典型特征。项目对边界层大涡模式发展及精细天气预报等具有实际应用价值，同时也在复杂地形边界层理论研究方面具有科学意义。

在复杂山地地形条件下，低层风场受地形影响较大，具有高度非均匀性。观测数据所能代表的范围非常有限，在这种情况下，利用数值模拟方法获得复杂地形条件下高分辨率的近地层风场资料就显得非常重要。本项目基于中尺度气象模式WRF和大涡模拟LES，构建多尺度模式WRF-LES。采用四重嵌套将水平分辨率从中尺度1km降至小尺度37m，以小海陀山赛事核心区域为研究对象开展风场精细模拟：1）结合观测，开展模式地形及土地利用静态数据集，模式水平、垂直分辨率，时间积分步长等模式框架设置的敏感性试验，对比分析边界层方案，评估、检验WRF-LES作为真实大气模拟工具在复杂地形区域的适用性；2）对比LES中三种常用的湍流参数化方案，测试其中关键参数对模拟风速的影响；3）在LES模拟区域入流边界上加入研发的入流边界湍流生成方案，激发、加速内部湍流快速和充足的生成；4）修正次网格地形参数化方案，修正WRF模式对平原、山谷处低层风速的高估和对山顶低层风速低估的系统性误差。结果分析表明，WRF-LES具有对复杂山地近地面风场开展超高分辨率模拟应用的潜力和价值，表现出很高的预报能力。基于该模式框架为冬奥会精细气象服务提供有力的技术支持，包括：1）为深入了解小海坨山赛区复杂地形区域冬季近地面风场情况，对冬季典型个例开展模拟分析；2）对赛场核心区域开展近地面风场精细化评估，提交冬奥组委中、英文评估报告，为赛时安排，赛事施工提供帮助；3）进一步研发百米分辨率实时预报系统，为冬奥气象预报团队提供次百米分辨率实时预报产品。