Dust devil in the Salt Wells Basin (Eightmile Flat) in April 2008
Chuck at Lounge of the Lab Lemming recently posted about a dust devil (AKA willy willy in Australia or Chindii in Navajo land), wondering about the formation of the inner core of a dust devil. I don't know the answer to his specific question - about why an inner core should look white when the dust it's picking up is red - but I did find a few links about our ever-present desert phenomenon. It may be that this is a research area worthy of further work, as much current research seems to be directed towards tornados. Fairly recent discovery of dust devils on Mars might spur more research on this planet, where we can actually examine these devils or spirits of the desert. Dust devils on Mars were first observed in the late 1970's and early 1980's during the Viking program and were (probably) first encountered on the ground during the 1997 and 1998 Pathfinder missions.
For the record, although most dust devils form on relatively calm, clear days, they also form underneath cumulus clouds that mark thermal uplift below the clouds. I personally observed one in west-central Nevada in the late 1980's that had formed on a playa from the ground up, in the usual fashion. A large, dark cumulus cloud sat overhead, and gradually a small funnel dropped from the cloud. The funnel cloud and dust devil briefly hooked together, forming what was technically, I suppose, a small tornado. I unfortunately no longer have a photo of that unusual event.
A few dust devil (and tornado) links:
- Dust devils at the Alaska Science Forum.
- Dust devils in Flagstaff at NOAA.
- Dust devils of Maricopa County from Glendale Community College.
- Dust devils and other atmospheric circulation phenomena from the Planetary Environment Research Laboratory.
- Tornado facts, including info on dust devils and whirlwinds from TORRO.
- Highly technical stuff about Rankine vortexes.
- An abstract about dust devil simulations and pressure drops in the core.
- Ask Jack about dust devils and tornados at USA Today Weather.
- Dust devils at Wikipedia.