Live Dust Devil? Options

[azstrummer]

Man, this looks an awful lot like a dust devil in the distance. What do you think?

[Bill Harris]

Dust devil activity should increase since Mars is at or near perihelion and the southern solstice. I figure that there is a lag time between the maximum insolation and the DD activity so later this Summer ought to be interesting.

--Bill

[dvandorn]

Remember, we have a certain baseline of observations from the earliest part of the mission. Spirit landed in late summer/early fall, local time, correct? And the DD activity at that time was minimal -- we never saw much in the way of them until we were well into the following spring.

We also saw the begining of DD season in early spring, and it seems to have peaked and has been trending down for a week or two, now.

I guess what I'm wondering is whether higher levels of insolation will, in fact, result in the formation of even more DDs? I think it's possible that the process of DD formation might not be directly related to insolation levels.

I also find it fascinating that DD formation seems almost more related to terrestrial tornado formation than simple terrestrial dust devil formation. Have you noticed how many of the larger DDs seem to start out with two, and sometimes more, small funnels dancing around the area in which the larger funnel shortly appears? This same fundamental observation has recently been made of terrestrial tornadoes -- that small, transient "whirlpools" dance and rotate around a larger low-pressure dip, "spinning up" the main funnel.

I think there are hints that we're seeing the same basic process in the Martian DDs, too.

Finally, I'll point out that whirlpool activity in fluid gas is driven more by pressure deltas than by temperature deltas, and that the Martian atmosphere's thinness gives other factors (including topography) more impact on pressure deltas than heating effects do. And observations from Viking, Pathfinder, MGS, MO, MEX and the MERs all show that local heating of the air by ground re-emission only strongly affects the air temperature for a few feet above the ground. Thermal homogenization occurs very, very low in the atmosphere. Topography, affecting air pressure directly and controlling most of the fine detail of lower atmospheric heating, seems to be the largest factor in local weather events. (Just look at how DD tracks are mostly isolated to very small patches, usually just off-center from the centers of large craters.)

-the other Doug

[Bob Shaw]

I wonder whether the view from on high helps to find the Dust Devils for us - perhaps we've been seeing more because we have a good view out to the plain, and not because there were fewer of them earlier in the Martian year.