Prediction of quasi-periodic oscillations in radiation fogs. Part I: comparison of simple similarity approaches.

Abstract

There is considerable controversy in the literature concerning fog formation. One set of observations suggests that fog forms during a lull in turbulence, while another set of observations suggests that increased turbulence leads to fog formation. A number of first-order closure techniques are applied to numerical simulations. The results show that fog formation and development is directly correlated with the magnitude of the eddy mixing coefficients. Larger turbulence generation leads to more rapid fog development and to larger liquid water contents. The rate at which the fog top grows is directly related to the rate at which turbulence lifts the inversion. During the mature fog stage, a series of fog dissipation and redevelopment episodes occur. Liquid water develops in the upper regions of the fog during the turbulently quiet periods. Subsequent destabilization of the atmosphere increases turbulence generation and mixes the upper- level liquid water to the surface, creating surface fog intensification. Quasi-periodic oscillations in fog parameters are largest in the upper regions of the fog and become progressively damped in the lower regions of a thick fog. These results are in qualitative agreement with the observations reported by Jiusto and Lala and support the hypothesis that there are distinct stages of fog development.-Authors