Dust to Dust: The Rooster Tail

Just so you don't get the idea that the rooster-tail of dust is peculiar to the Jornada, I need only remind the Toolik Lake CC-trippers that the pipeline highway is a dirt road and John Hobbie was, even then, interested in the rooster tail of dust problem.

He asked me how high the rooster tail gets.

My answer was that it depended on the speed of the vehicle and its aerodynamic form. Those two variables determined how big the dust-laden wind eddies would get within the rooster tail. I told John dust eddies heights were on the order of three times the length of the vehicle.

Well, that is a good of rule of thumb, but the stability of the atmosphere also must be factored into the calculus of rooster-tail morphology. On days when the air is very stable, e.g. when there is an inversion present, upward motions are suppressed and the top of the rooster tail sort of flattens off quickly.

If, on the other hand, the air is unstable, warm at the surface with rapid cooling as you go upward, the upward motions are not suppressed and the height of the rooster tail can be quite high.

In places like the Jornada, where the surface temperature can get quite high, we get supercritical, mirage-quality, lapse rates and upward motions, which once started can reach great heights.

These are the kind of days that dust devils might get a kick-start by a jack rabbit.

This will be blogged on in due time.


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