UNWRAPPING THE WHIRLWIND; MEASURING NATURAL DUST DEVILS

The Eldorado Valley Dust Devil Project in southern Nevada has developed a unique chase system to actively pursue and probe dust devil vortices that form over the desert playa surface. Dust devils have been characterized as capable of lofting substantial masses of sift and dust to considerable heights (by Gillette & Sinclair, 1990, Metzger, and others). Their effective erosion of soil must derive from the convective thermodynamics that power the vortices. Unfortunately, the scarcity of detailed measurements of dust devils hampers both the ability to develop theories that articulate their behavior and to test the theories already proposed.

The chase rig consists of a terrain-following 5-m vertical mast supporting 30 instruments that profile wind speed, temperature, pressure, and humidity. Additional single-level instruments measure particle impacts, particle charge states, and UV insolation levels (several of which were developed for the Beagle2 Mars lander). Dust devils could not sustain their thermal engine when ambient winds dropped below 2 m/s. Conversely, vortex structure was disbursed and destroyed when ambient winds exceeded 8 m/s, although in both cases short-lived vortices could develop. Under such conditions, a dozen events were well documented by datalogger and cameras. This report will present the latest findings from the 2004 field season as we strive to assimilate these simultaneous data sets.