Experimental study of the effect of wind on the stability of water ice on Mars

Abstract

We have studied the effect of wind velocity on the sublimation rate of pure water ice under martian conditions. Measurements were made for wind velocities ranging from 0.7 to 11.4 m s −1, a typical range observed by the meteorological instruments on the surface of Mars, and at − 15 ° C a value typical of the daily high temperature for most of the year at the Pathfinder landing site. At this temperature, and for a low-humidity environment (relative humidity around 1%) sublimation rates increase following a linear trend of equation E S = 0.68 + 0.025 V ( E S is the sublimation rate in mm h −1 and V is the wind speed in m s −1). In high relative humidity (30–35%) atmospheres, the effect of wind velocity is negligible, and the sublimation rate remains nearly constant at 0.33 ± 0.04 mm h −1 . Pure forced convection theory did not provide a satisfying description of the data in terms of the range of values and their wind speed dependency. Therefore, a new semi-empirical expression for the sublimation rate that combines free and forced convection was developed using analogy with heat transfer models. Using this expression, sublimation rates of ice as a function of wind velocity for any temperature can be calculated. In general, temperature is more important that wind speed and atmospheric humidity in determining the rate of sublimation of ice on Mars.