RUNNING WITH THE WHIRLWINDS - 25 YEARS OF CHASING DUST DEVILS AND THE TERRAIN THEY SPRING FROM

More than a visual desert oddity, dust devil vortices play a substantial role in the transfer of heat from arid surfaces up into the atmospheres of Earth and Mars, and in the process loft considerable quantities of fine soil particulates which travel regionally and globally. This presentation will review the author’s past 25 years of field studies into dust devil activity on North and South America, as well as Mars, and report on current work into regional atmospheric dynamics in hope of using them as proxies for circulation cells which are otherwise undetectable. Although dust-laden vortices can form over a variety of arid soils, including those containing surface roughness elements (e.g. bushes or boulders) which can impede conventional shear winds, they are also severely hampered by other common roughness elements (e.g. grass stubble or pebble-rich pavements). Grain size variations are less constraining than expected but some percent of silt & clay is required (or volcanic ash), as are abrasive sand-sized or larger “tools”. Dust devil shape, longevity and column dimensions vary in response to both the terrain’s aerodynamic qualities and the immediate local wind conditions. All of these factors mean that some surface properties can be ascertained from afar solely by the appearance of a dust devil (useful when limited surface access or lander assets prevent an up-close examination of those more remote surfaces). Seasonal variations in dust devil production have been tied both to weather trends as well as near-surface soil moisture etc. conditions. In situ sediment loading measurements indicate that these vortices are moving and re-working tremendous amounts of soil particulates, providing rapid ascension to great heights. This can strongly contribute to regional air quality issues, sediment deflation or the mixing of source materials. Once airborne, dust motes are readily heated by insolation and influence the thermodynamics of that air mass. They may assist smog formation, carry bacterial “hitch-hikers”, deliver soil nutrients to remote barren environments, and present dangers for human flight and spacecraft EDL activities.