Martian and terrestrial dust devils:: Test of a scaling theory using Pathfinder data

The Mars Pathfinder meteorological station recorded wind, pressure, and temperature fluctuations that have been interpreted as dust devils: warm-core vortices that form at the bottom of convective plumes. We apply a scaling theory [Renno ef al., 1998], developed to explain terrestrial dust devil observations, to test the validity of this interpretation and to provide a simple physical interpretation of the general characteristics of Martian dust devils. The theory is based on the thermodynamics of heat engines and predicts the central pressure and the wind speed of the convective vortices. Our findings ate as follows: For the best documented candidate event (sol 25), observed wind and pressure fluctuations are consistent with those predicted by the model and hence strengthen the interpretation of this case as a dust devil. A number of other candidates, less well documented, however, also are consistent with passage of a dust devil over or near the lander. Temperature fluctuations observed on other sols permit dust devils an order of magnitude larger than the ones measured by the meteorology package. The strongest dust devils predicted by our theory have a central pressure deficit of about 50 Pa and wind speed of about 60 m s(-1). The strongest dust devils are capable of lofting dust and hence support the interpretation of selected Pathfinder images as showing the passage of dust devils within sight of the lander.