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徐慧燕, 徐亚钦, 王智, 朱佩君, 李小凡, 翟国庆. WRF模式中QNSE方案的湍流长度尺度系数的调整试验研究[J]. 大气科学, 2017, 41(2): 357-371. DOI: 10.3878/j.issn.1006-9895.1606.16108
引用本文: 徐慧燕, 徐亚钦, 王智, 朱佩君, 李小凡, 翟国庆. WRF模式中QNSE方案的湍流长度尺度系数的调整试验研究[J]. 大气科学, 2017, 41(2): 357-371. DOI: 10.3878/j.issn.1006-9895.1606.16108
Huiyan XU, Yaqin XU, Zhi WANG, Peijun ZHU, Xiaofan LI, Guoqing ZHAI. Modification Tests for the Coefficient of Turbulent Mixing Length Scale in QNSE Scheme in the WRF Model[J]. Chinese Journal of Atmospheric Sciences, 2017, 41(2): 357-371. DOI: 10.3878/j.issn.1006-9895.1606.16108
Citation: Huiyan XU, Yaqin XU, Zhi WANG, Peijun ZHU, Xiaofan LI, Guoqing ZHAI. Modification Tests for the Coefficient of Turbulent Mixing Length Scale in QNSE Scheme in the WRF Model[J]. Chinese Journal of Atmospheric Sciences, 2017, 41(2): 357-371. DOI: 10.3878/j.issn.1006-9895.1606.16108

WRF模式中QNSE方案的湍流长度尺度系数的调整试验研究

Modification Tests for the Coefficient of Turbulent Mixing Length Scale in QNSE Scheme in the WRF Model

  • 摘要: 边界层参数化方案中湍流混合对数值模拟起着重要的作用,湍流混合作用的恰当描述对于温度、湿度、风场以及降水的准确模拟至关重要。我国长江中下游流域人口密集,暴雨灾害频发,很有必要寻找一种适合该地区降水模拟的边界层参数化方案。本文运用WRF(Weather Research and Forecasting)中尺度数值模式,以QNSE(Quasi-Normal Scale Elimination)边界层参数化方案为基础,将其中湍流混合长度尺度系数调整为可变参数。本文将Noh et al.(2003)提出的Prandtl公式与Janjić提出的修正湍流长度尺度系数的方法相结合,通过考虑非局地项的强迫、地表稳定度与边界层高度对湍流长度尺度系数的影响,强调大气的动力结构特征与热力结构特征对湍流混合的共同影响,从而提高QNSE边界层参数化方案在不同地理环境下的模拟能力。文章通过进行长江中下游地区的典型暴雨试验,将调整参数后的QNSE方案与原方案进行比较,重点分析调整参数后的方案与原方案对关键基本气象要素场、边界层结构特征以及降水的模拟能力,并将模拟结果与观测结果进行对比,结果表明:调整参数后的方案一定程度上改进了地表温度、边界层结构以及降水的模拟效果。进一步研究表明,调整参数后的方案主要通过改变边界层混合缓解水汽混合比、位温模拟方面的误差。

     

    Abstract: Appropriate description of turbulence in PBL (planetary boundary layer) is essential for numerical weather prediction and simulation. Proper treatment of turbulence may have an important influence on the simulation of meteorological fields, such as temperature, moisture, wind speed and precipitation. Heavy rainfall event is frequent in the lower reaches of the Yangtze River and it is necessary to obtain a suitable PBL scheme for this region due to its dense habitability. In this study, based on the QNSE (Quasi-Normal Scale Elimination) planetary boundary layer scheme in the WRF (Weather Research and Forecasting) Model, the coefficients of the TLS (turbulent mixing length scale) in the Mellor-Yamada formulation were modified to be varying based on the application of the Prandtl formula. The MCTLS (modified coefficients of TLS) are dependent on the PBL height and surface stability, and a nonlocal term was imposed on MCTLS, thereby emphasizing the comprehensive impacts of the atmospheric dynamic and thermal structures on turbulent mixing. WRF model simulations using the original PBL scheme and the PBL scheme with the MCTLS were conducted over the lower reaches of the Yangtze River and results were compared to measurements. Improvements in the near-surface temperature, the planetary boundary layer structure and the rainfall simulations have been found. More specifically, the simulations with the MCTLS were shown to alleviate biases in the potential temperature and water vapor mixing ratio by altering turbulent mixing.

     

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