Mars: Wind friction speeds for particle movement

Abstract

Wind friction threshold speeds (V * t) for particle movement were determined in a low pressure boundary layer wind tunnel at an atmospheric pressure of 5.3 mb. The results imply that for comparable pressures on Mars, the minimum V * t is about 2.5 m/sec, which would require free‐stream winds of 50 to 135 m/sec, depending on the character of the surface and the atmospheric conditions. The corresponding wind speeds at the height of the Viking lander meteorology instrument would be about a factor of two less than the free stream wind speed. The particle size most easily moved by winds on Mars is about 160 µm; particles both larger and smaller than this (at least down to about 5 µm) require stronger winds to initiate movement. The results presented here are in general agreement with previously reported values of V * t for particles 12 µm to 300 µm derived from one atmosphere tests, but are inconsistent with values for particles larger than about 300 µm.