Artificial Dust Devils?

[Geoff Boyle]

While conducting airside operations at YXX, I noticed that a number of dust devils formed in the field adjacent to the primary runway. I can't say the weather conditions were "favorable" most of the time, so I wondered if the aircraft or equipment we use might play a role in the formation of these dust devils. To me it makes sense, since the jet wash from commercial aircraft would probably contribute to the vorticity.

NOTE: I haven't seen any since mid September

 

[Andrew Khan]

Yeah, I have heard of this, on more than one occasion. It apparently has to do with the jet's winds, that are being emitted, and then clashing with the other 'natural' winds, and thus creating vorticity.

 

[Skip Talbot]

I saw this for myself when I got to tour a control tower once. The adjacent field was filled with dust devils. I assumed at the time though they were naturally occuring because the traffic was pretty light at this small regional airport. However, airplanes do generate strong wingtip vorticies that can last for a few minutes in some cases. The jumbo jets make vorticies big enough to send smaller aircraft out of control. i could see the horizontal vorticity being caught in the thermal updraft of a field at the end of the runway and sparking a dust devil.

 

[Dan Robinson]

On my flight to Denver earlier this year, we passed very close to a fresh contrail from another plane. There were two well-defined, thin parallel tubes of condensation running the length of the contrails.

 

[Andrew Khan]

I don't know why, but something goes on with the turbulence, and the intense wind given off from the Airplane...

 

[David Wolfson]

Years of casual but very interested observation of dust devils have persuaded me that they are produced by two quite distinct physical mechanisms.

The first is the traditional explanation whereby a thermal bubble forms over superheated ground, breaks off and rises, entraining surface air and concentrating its vorticity. These devils form when there is low wind velocity for a significant height AGL and thus absent turbulent downward momentum transfer. These visually resemble landspouts.

The second occurs when there is intense surface heating combined with enough turbulent downward momentum transfer to raise significant dirt in gusts but not so much as to generally displace dirt. The devils in this case owe their vorticity to the vertical translation of the wind speed shear with altitude. These visually resemble gustnados.

In each case I believe the sensient heat released by raising and dispersing the surface dirt is important to their persistence and intensity. I'll leave it to recent physics students to confirm or dispute the claim that a moderate mass of surface dust contributing, say, 30C of heat to the ambient air would be sufficient to maintain a vigorous vortex against the drag of entrainment and surface friction. This is the same mechanism as occurs in fire devils, but much less intense.

The airplane induced dust devils would be of the second kind where the horizontal shear vorticies are produced by the wings rather than by the ambient wind. FWIW, IMHO.

 

[Geoff Boyle]

In each case I believe the sensient heat released by raising and dispersing the surface dirt is important to their persistence and intensity.

That was the main thing I was wondering about. I know that the jet-wash can produce dust devils, but they shouldn't last more than a few seconds. Though, some lasted at least 2 minutes.

 

[Andrew Khan]

There must have been some favorible, low level conditions, for them to have a sustained life cycle...possible low level vorticity, induced by other prominent factors, excluding the ones rendered by the aircraft.

 

[David Wolfson]

I'd guess that the best conditions would be light winds, full solar heating near mid-afternoon, and no low-level inversion. Normal thermals rising off the hot field might then twist the horizontal wing vorticies enough vertical to kick up hot dirt and keep the vortex stoked. Insolation drops way off in the fall and with it the differential heating of the field.