On the Reliability of the Parameterization of Microphysics in Fog Models

Abstract

The relationships between the mean terminal speed of fog droplets (vE) and the liquid water content (W), and between the integral volume droplet absorption coefficient (σE) and W, have been examined on the basis of 107 experimental fog droplet size spectra selected from the literature, in order to investigate the reliability of parameterizing the microphysics, in fog models, through W. The results show that a weak correlation exists between vE and W, the values of the linear correlation coefficients (R) being 0.12, 0.30, ?0.19 and 0.67, for valley, advection, radiation and artificial fog, respectively. Thus parameterizations of vE through W only are generally unreliable, and other parameterizations, in terms of more than one parameter, should be developed. On the other hand, a good correlation between σE and W has been found, with R = 0.98, 0.87, 0.91 and 0.99 for the fog types indicated above. Comparisons between the values of σE and those obtained by the best-fit lines and by the parameterizations used in fog models, together with the evaluation of the effect of such approximations on the radiative cooling profile, have been carried out.