Adaptive Improvement Of MYNN Boundary Layer Scheme And Its Simulation Of A Sea Fog In The Yellow Sea

Sea fog is a weather phenomenon that that occurs over the ocean and the horizontal visibility is hindered due to a large number of water droplets suspended in the atmospheric boundary layer over the ocean.The yellow sea is one of the foggy areas along the coast of China.The poor visibility in the atmosphere associated with sea fog which induces economic losses in sea transportation is increasing with the upgrade of human activities in coastal areas.In order to improve the model ability of sea fog simulation,it is necessary to establish a high-resolution numerical model.On the other hand,the dynamic core of the numerical model can describe a part of turbulent motion,even though another part of the turbulence properties must be parameterized when the model grid spacing is comparable with the length scale of energetic turbulent eddy as the resolution of numerical model becoming higher and higher.This leads to the “grey-zone” issue.The traditional PBL scheme is not suitable for the so-called “grey-zone” problem.In order to improve the capability of PBL scheme in multi-scale model,including the “grey-zone” simulation,we enhance the Mellor-Yamada-Nakanishi-Niino(MYNN)scheme by introducing non-local turbulent parameterization of heat and moisture turbulent flux and mesh-scale dependent turbulent length scale for self-adapting arrangement of PBL scheme in a wide model resolution based on the Reynolds average numerical simulation.The self-adapting MYNN scheme is used to simulate a sea-fog case in Huanghai region on February 26,2014 using the one-way nesting Weather Research and Forecast(WRF)model with horizontal resolution of 3 km and 1 km,or 1.5 km and 0.5 km in comparison with the original MYNN scheme.The new MYNN scheme demonstrates reasonable vertical turbulent transport of heat and moisture in kilometer resolution model.Compared with satellite imageries,the integrated low-level cloud water shows similar horizontal coverage of sea fog in different resolution models with the self-adapting MYNN scheme.Vertical profiles of temperature and humidity also illustrate in well accordance with the ERA-interim reanalysis data which improves obviously the original scheme.Preliminary results show the possibility of its self-adapting ability in multi-scale models.