尺度自适应大气边界层参数化改进及其对一次海雾的数值模拟研究

Scale-aware parameterization of atmospheric planetary boundary layer and its application to sea fog simulation

大气边界层湍流运动是地球大气运动最重要的能量输送过程之一。当数值模式分辨率接近活跃含能湍涡长度尺度时,湍流运动被部分解析,被称为“灰色区域”,传统的边界层方案不适合此时模式湍流问题的描述。为了提高模式边界层方案在包括“灰色区域”的不同网格尺度上的描述能力,适应不同分辨率模式的需要,在雷诺平均湍流理论基础上,修正Mellor-Yamada-Nakanishi-Niino(MYNN)方案湍流长度尺度参数和非局地湍流的参数表达,改进湿度和温度在“灰色区域”的湍流输送参数化及对网格尺度的自适应能力。利用改进的MYNN尺度自适应方案,分别采用3 km和1 km、1.5 km和0.5 km分辨率单向嵌套网格WRF中尺度模式,对2014年2月26日的一次黄海海雾过程进行模拟试验,检验不同分辨率下改进后的MYNN大气边界层参数化方案的合理性和对海雾的模拟效果。尺度自适应MYNN大气边界层参数化方案在千米级网格尺度上获得稳定、合理的湍流垂直输送计算结果。参照雾区卫星云图,不同分辨率模式低层云水混合比模拟结果具有稳定表现,模拟的雾区分布和温度、湿度等物理量结构都较好地再现了再分析“观测事实”,初步表明该参数化方案有较高的网格尺度自适应能力。

Turbulent mixing in the atmospheric planetary boundary layer(PBL)is one of the most important process to transport energy to maintain atmospheric movement.As the model grid spacing is close to the length scale of energetic turbulent eddy,turbulence can only be partly resolved.This is called the"grey-zone"problem.Traditional PBL schemes are not suitable for the description of turbulent transport in numerical models.In order to improve the capability of PBL scheme in multi-scale models,including the"grey-zone"simulation,the Mellor-Yamada-Nakanishi-Niino(MYNN)scheme was improved by introducing non-local turbulent parameterization of heat and moisture turbulent flux and mesh-scale dependent turbulent length scale for self-adapting arrangement in a wide range of model resolutions based on the Reynolds average numerical simulation.The self-adapting MYNN scheme is then used to simulate a sea fog case in the Huanghai region that occurred on 26 February 2014 using the one-way nesting Weather Research and Forecast(WRF)model with horizontal resolutions of 3 km and 1 km,and 1.5 km and 0.5 km,respectively.Results are compared with simulations using the original MYNN scheme.The new MYNN scheme demonstrates capability for reasonable simulation of vertical turbulent transport of heat and moisture in a kilometer-resolution model.Compared with satellite images,the integrated low-level cloud water shows a similar horizontal coverage of sea fog in the simulations with different resolutions using the self-adapting MYNN scheme.Vertical profiles of temperature and humidity also illustrate structural distributions that agree better with the ERA-interim reanalysis data compared with results simulated with the original scheme.Preliminary results show that the self-adapting MYNN scheme can be applied in multi-scale models.