The stratocumulus nature of fog

Abstract

Landsat Multispectral Scanner (MSS) and Thematic Mapper (TM) digital data are used to remotely sense fog properties. These include fog cell size distribution, cell aspect ratio (the ratio of the length of the major and minor axes of the cells), and cell orientation angle. The analysis is carried out for four fog scenes, three high-inversion radiation fogs in central California, and one advection fog in eastern South Dakota. Results for these initial fog studies indicate that 1) fogs are stratocumulus in nature, being composed of individual cellular structures; 2) the reflectance properties vary strongly across the cells, suggesting considerable variation in liquid water content; 3) fogs often are patchy, often revealing surface features between fog cells; 4) the ratio of wavelength (λ) between cells and the height of the boundary layer (h) is λ/h ~ 2-3, in agreement with values obtained for Benard cells and longitudinal rolls observed in cloud systems; 5) the typical horizontal aspect ratio of fog cells is about a factor of 2: and 6) observed quasi-periodic oscillations of measured fog variables may be caused by advection of the cellular structures across the observational site.