摘要
Radiation fog seriously threatens traffic safety,human health,and the development of low-altitude economy in North China.However,there are still great uncertainties in the numerical forecasting of radiation fog,and turbulence parameterization is one of the key uncertainty sources.In this study,the spatiotemporal variations of turbulent diffusion were analyzed by using the 5-level tower turbulence observations in Tianjin during four radiation fog episodes from 2016 to 2019.Based on the observation analysis,an improvement to the minimum eddy diffusivity of heat(K_(hmin))in the Yonsei University(YSU)scheme was implemented in the Weather Research and Forecasting(WRF)model.K_(hmin) is the minimum threshold of the heat eddy diffusion coefficient(K_(h))defined in the model(0.01 m^(2) s^(-1) in YSU scheme)to avoid the physically unrealistic situations where the model calculates zero turbulent atmosphere under strong stability conditions.However,observations in this study revealed that the 10th percentile of K_(h) at night was mostly lower than 0.01 m^(2) s^(-1),indicating that the model may overestimate the nighttime turbulent diffusion during the fog episodes.Sensitivity experiments demonstrated that changes in K_(hmin) significantly altered the simulation of no cturnal boundary layer(NBL)structure,while exerting a rather ne gligible impact during the daytime.Reducing K_(hmin)resulted in a lower surface temperature and a stronger inversion,thereby facilitating the formation of radiation fog.When K_(hmin) was reduced from 0.01 to 0.0001 m^(2) s^(-1),the nighttime Threat Score(TS)and Probability of Detection(POD)for fog forecasting increased by 0.029 and 0.053,respectively.Conversely,increasing K_(hmin) led to a weaker inversion and the dissipation of fog.This study highlights the importance of K_(hmin) in the planetary boundary layer(PBL)scheme for simulating fog,and also provides a novel perspective for improving fog forecasting.Specifically,a smaller K_(hmin) value may be more appropriate for simulating radiation fog.
基金
Supported by the National Natural Science Foundation of China(42205092,42205009,and 42105084)
Applied Foundational Research Project of Tianjin(22JCQNJC00370)
Scientific Research Project of Tianjin Meteorological Bureau(202309ybxm04 and 202306ybxm02)
Open Project of Tianjin Key Laboratory of Oceanic Meteorology(2024TKLOM04)
Nanjing Institute of Meteorological Science and Technology Innovation Arctic Pavilion Open Research Fund(BJG202404)
Science and Technology Collaborative Innovation Fund of Bohai Rim Region(QYXM202112 and QYXM202202)。
