Surface deposition of marine fog and its treatment in the Weather Research and Forecasting (WRF) model

There have been many studies of marine fog, some using Weather Research and Forecasting (WRF) and other models. Several model studies report overpredictions of near-surface liquid water content (Qc), leading to visibility estimates that are too low. This study has found the same. One possible cause...

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Bibliographic Details
Published in:Atmospheric chemistry and physics 2021-10, Vol.21 (19), p.14687-14702
Main Authors: Taylor, Peter A, Chen, Zheqi, Cheng, Li, Afsharian, Soudeh, Weng, Wensong, Isaac, George A, Bullock, Terry W, Chen, Yongsheng
Format: Article
Language:English
Subjects:
Aerosols
Analysis
Atmospheric boundary layer
Atmospheric models
Atmospheric research
Cloud droplets
Deposition
Droplets
Fog
Fog droplets
Fog water
Forecasting
Gravity
Heat
Liquid water content
Meteorological research
Moisture content
Numerical weather forecasting
Radiation
Rain
Roughness
Roughness length
Turbulence
Vegetation
Velocity
Visibility
Water
Water content
Water droplets
Water drops
Water vapor
Water vapour
Weather
Weather forecasting
Wind
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Summary:There have been many studies of marine fog, some using Weather Research and Forecasting (WRF) and other models. Several model studies report overpredictions of near-surface liquid water content (Qc), leading to visibility estimates that are too low. This study has found the same. One possible cause of this overestimation could be the treatment of a surface deposition rate of fog droplets at the underlying water surface. Most models, including the Advanced Research Weather Research and Forecasting (WRF-ARW) Model, available from the National Center for Atmospheric Research (NCAR), take account of gravitational settling of cloud droplets throughout the domain and at the surface. However, there should be an additional deposition as turbulence causes fog droplets to collide and coalesce with the water surface. A water surface, or any wet surface, can then be an effective sink for fog water droplets. This process can be parameterized as an additional deposition velocity with a model that could be based on a roughness length for water droplets, z0c, that may be significantly larger than the roughness length for water vapour, z0q. This can be implemented in WRF either as a variant of the Katata scheme for deposition to vegetation or via direct modifications in boundary-layer modules.
ISSN:1680-7324
1680-7316
1680-7324
DOI:10.5194/acp-21-14687-2021