边界层参数化对海南岛山地环流结构和湍流特征模拟的影响

Impact of planetary boundary layer parameterizations on simulated mountain circulation structure and turbulence characteristics over the Hainan Island

本文基于WRF-ARW(V4.0)中尺度数值模式,选用耦合同一近地层参数化方案(Eta)的五种边界层参数化方案(MYJ、MYNN2、MYNN3、BouLac、UW),对2020年5月1—2日海南岛一次典型山地环流个例进行模拟,对比分析了这五种方案所模拟的山地环流结构和湍流特征的差异,旨在为模式应用于山地环流研究和模式改进提供一定的科学依据.研究结果表明,这五种湍流动能边界层参数化方案均能模拟出山谷风特征,对环流结构和湍流特征的影响表现为谷风时段大于山风时段.对于山地环流水平结构的模拟,因平原风推进距离的不同,五种方案模拟的近地面风速差异可达4 m·s^(-1)以上,其中MYJ方案模拟的谷风最强盛,而MYNN3方案最弱,山区多为静风或小风.对于山地环流垂直结构的模拟,MYNN2、UW方案模拟的谷风环流较强,表现为谷风厚度较厚,推进距离较远,同时由于模拟的谷风环流可越过山顶,从而模拟的高海拔地区上升区的覆盖范围和强度均较大;MYJ、BouLac方案模拟的谷风环流均未能越过山顶,且其中BouLac方案的平原风环流未能与上坡风环流耦合;而MYNN3方案模拟的环流结构最不明显.湍流特征对比分析表明,五种方案模拟的湍流动能强度和分布特征存在显著差异,其中MYNN2方案湍流混合最强,MYJ方案最弱.由于MYNN2方案下垂直湍流混合较强,大气不稳定度增加,因此其对应的谷风厚度较大,同时该方案模拟的边界层结构与实况最为接近,更适用于海南岛山地环流的模拟.

To investigate the sensitivity of the mountain circulation structure and turbulence characteristics to boundary layer turbulence process parameterizations over the Hainan Island,five turbulent kinetic energy boundary layer schemes(MYJ,MYNN2,MYNN3,BouLac,and UW)coupled with the same surface layer parameterization scheme(Eta)in the Weather Research and Forecast model(WRF-ARW V4.0),are designed to simulate a typical mountain circulation case from May 1 to 2,2020.Results show that all schemes predict the mountain-valley winds,while the differences among them are significant during the daytime.The difference in near-surface wind speed can reach more than 4 m·s^(-1) among the five boundary layer schemes due to the different propagation distance of plain wind.It is found that the valley wind is the strongest in MYJ scheme,while the weakest in MYNN3 scheme.In the simulation of vertical structure,MYNN2 and UW schemes produce the strongest valley circulation which is characterized by a deeper valley-breeze depth and further inland penetration.Further,the simulated valley wind circulation can cross the peak of mountains,making the upward motion stronger and wider in the mountains above 600 m height.While the circulation of MYJ and BouLac schemes fails to cross the mountaintop,and the plain wind circulation is not well coupled with the upslope wind circulation also in BouLac scheme;the circulation structure is not clear in MYNN3 scheme.The analysis of turbulence characteristics shows that there are obvious differences in the intensity and distribution characteristics of turbulent kinetic energy of the five schemes,among which the turbulent mixing in MYNN2 scheme is the strongest and that in MYJ scheme is the weakest.Due to the stronger vertical turbulent energy mixing of the MYNN2 scheme,the atmospheric instability increases and the corresponding valley-breeze depth is deeper.At the same time,the boundary layer structure of MYNN2 scheme is closer to the actual situation,which means that this scheme is more suitable for the simulation of mountain circulation in Hainan Island.