Diurnal behaviour of water on Mars

A numerical model of the diurnal transport of water across the Martian surface is developed. The atmospheric boundary layer is modeled in terms of local radiative-convective processes, and radiative effects of ice fogs near the surface are included. Diffusion of water in the ground is treated for the cases of adsorption and condensation. The model is applied to the diurnal variation of water vapor in the atmosphere as observed by Barker (1974). The morning rise in the amount of water vapor can be explained in terms of the evaporation of ground fogs. The evening decrease is compatible with the model if adsorption dominates in the soil. The average level of vapor concentration requires that the atmosphere above the boundary layer be relatively dry. The ground fogs persist until midmorning and should be observable. Some consequences of these conclusions are discussed.