DIFFERENTIAL SURFACE HEATING AND ITS POTENTIAL EFFECTS ON DUST DEVIL FORMATION

Dust-laden vortices (i.e., dust devils) form as a result of convective heat transfer between the surface and the air in contact with it. This air heats up quickly, and becomes adiabatically unstable, rising to form convection cells. In some settings, formation appears to be favored by aerodynamically large roughness elements, which shields pockets of preferentially heated air. We hypothesize that surfaces which heat up at faster rates and have sufficient roughness elements should spawn greater numbers of dust devils given other necessary factors are met.

This study was conducted in Smith Creek Valley, Nevada, on a dry lakebed playa where dust devils are common and actively studied. The heating and cooling rates of four distinct geomorphological surface types were measured over three 24-hour cycles. The four prominent surface types identified at the valley floor include silt-dominated playa, gravel-imbedded playa, biocrust covered sediment, and creosote/mesquite bush hummocks. Each surface is represented by 6-7 sample sites, and temperature was measured using an infrared thermometer and thermal imaging camera. We recorded temperatures at theoretical maximum and minimum times, and subsequent maximum with 2 intermediate time periods over a 24-hour period. For each surface type, we collected representative sediment samples for sieving analysis and color ID from a Munsell color chart.

Preliminary results show that bush hummocks and biocrust surfaces had heating rates and maximum temperatures higher than the playa and gravel-imbedded playa. The 5:00-8:30 morning heating rates averaged between all three cycles show bush hummocks heated at 9.9° C/hr, biocrust at 8.25°C/hr, gravel imbedded playa at 5.83°C/hr and playa at 5.17°C/hr. Average maximum temperatures followed the same pattern, with bush hummocks heating to 52.8°C, biocrust heating to 52.9°C, gravel heating to 41.5°C, and playa heating to 40.9°C. The data suggest that with both greater heating rates and maximum temperatures, dust devils should begin forming earlier and form preferentially over bush hummock and biocrust surfaces. Additional results will be presented comparing the relationships of surface properties and atmospheric conditions to solar heating, and their influence on regional air temperatures at different heights throughout the day.