Formation,Evolution, and Dissipation of Coastal Sea Fog |
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Authors: | Email author" target="_blank">Darko?Kora?inEmail author Joost?A?Businger Clive?E?Dorman John?M?Lewis |
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Institution: | (1) Desert Research Institute, Reno, Nevada, U.S.A.;(2) University of Washington, Seattle, Washington, U.S.A.;(3) Scripps Institution of Oceanography and San Diego State University, San Diego, California, U.S.A.;(4) National Oceanic and Atmospheric Administration, Severe Storms Laboratory, Norman, Oklahoma, U.S.A.;(5) Desert Research Institute, 2215 Raggio Parkway, Reno, Nevada, 89512, U.S.A. |
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Abstract: | Evolution of sea fog has been investigated using three-dimensional Mesoscale Model 5 (MM5) simulations. The study focused
on widespread fog-cloud layers advected along the California coastal waters during 14–16 April 1999. According to analysis
of the simulated trajectories, the intensity of air mass modification during this advection significantly depended on whether
there were clouds along the trajectories and whether the modification took place over the land or ocean. The air mass, with
its trajectory endpoint in the area where the fog was observed and simulated, gradually cooled despite the gradual increase
in sea-surface temperature along the trajectory. Modelling results identified cloud-top cooling as a major determinant of
marine-layer cooling and turbulence generation along the trajectories. Scale analysis showed that the radiative cooling term
in the thermodynamic equation overpowered surface sensible and latent heat fluxes, and entrainment terms in cases of the transformation
of marine clouds along the trajectories. Transformation of air masses along the trajectories without clouds and associated
cloud-top cooling led to fog-free conditions at the endpoints of the trajectories over the ocean. The final impact on cloud-fog
transition was determined by the interaction of synoptic and boundary-layer processes. Dissipation of sea fog was a consequence
of a complex interplay between advection, synoptic evolution, and development of local circulations. Movement of the high-pressure
system over land induced weakening of the along-shore advection and synoptic-pressure gradients, and allowed development of
offshore flows that facilitated fog dissipation. |
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Keywords: | Lagrangian framework Mesoscale model 5 (MM5) Mesoscale simulations Offshore fog Radiative cooling U S West Coast |
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