A maritime boundary-layer model for the prediction of fog |
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| Authors: | Edward H Barker |
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| Institution: | (1) Naval Environmental Prediction Research Facility, Monterey, Calif., USA |
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| Abstract: | A two-dimensional boundary-layer model is described. The model is designed to predict and study the effects of meteorological changes on the formation and dissipation of fog and stratus. Radiational heat loss along with the transport of static energy, moisture and momentum are treated. Cloud droplet distributions are parameterized using a gamma distribution from which radiative properties and droplet fall velocities are computed. Turbulent exchange coefficients are calculated using the Monin-Obukhov theory of similitude which accounts for variations in atmospheric stability. Although the boundary-layer depth depends only on turbulent intensity during stable atmospheric conditions, its growth during unstable conditions is determined from the capping inversion's intensity and the amount of turbulence generated at the surface.Several experiments are presented which demonstrate the effects of various meteorological parameters on the formation and duration of stratus and fog. Energy-budget analyses show the importance of each of the physical processes being modeled.Although not new, radiative transfer processes are shown to be extremely important in the transfer of heat from the boundary layer and in the process of fog formation. Fog formation location is highly sensitive to the moisture content upstream, whereas changes in wind speed had much less effect in the variance of fog location.Numerical experiments with other processes such as back radiation from the atmosphere, haze and cloud droplet population, are described and shown to have smaller effects. |
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