Dust Devils of the '07 season Options

[Juramike]

Has anyone tried to relate the images of dust devils that have been captured on camera with their tracks on the ground in the from-orbit images?

-Mike

[Doc]

Interesting how tracks seem to cross the northern hills, and some craters. But they don't seem to cross the larger hills.

Don't know if dust devils are disrupted by the higher terrain, or if the higher terrain landscape doesn't show tracks.
-Mike

I believe it is indeed the higher terrain that disrupts the DD (ever heard of a tornado climbing Everest).
The hills act like some sort of dam for DD.

[paxdan]

Has anyone tried to relate the images of dust devils that have been captured on camera with their tracks on the ground in the from-orbit images?
-Mike

Now THIS is a good idea.

[slinted]

7 MRO CTX images of the Columbia Hills, taken from Spirit sol 1046 through Spirit sol 1207.


High res

Also, here's a 6 frame difference-image animation showing the changes from one frame to the next. The alignment/brightness errors between frames make it very messy looking, but I think it does a decent job showing the changing trend in wind direction over the sequence.

[climber]

The area is rather active !
We can't see the whole picture but, it seams to me that the hills area is much more active than the plain (North-East & South-West).
We've got some DD that went distinctly pretty close to where Spirit is. I'm wondering how far from the visible paths can we feel some noticeable wind.

[dvandorn]

What strikes me most strongly about this montage is how consistently light and streak-free the surface around the Hills looks at the beginning of last spring/summer's dust devil season.

If we assume that most every dust devil season leaves the area as streaked as the Sol 1207 image appears, then there is obviously a process in place that erases the streaks every winter.

Obviously, the global dust storm of this past summer is one such mechanism -- but there was no global dust storm (or even a localized dust storm) between the prior dust devil season and this last one.

Pretty impressive testament to the power of normal winds to wipe away such streaks every year.

-the other Doug

[Shaka]

Dare I suggest that it is a debatable point whether DD streaks are "wiped away by winds"
or covered over by dust settlement?

[Doc]

Dare I suggest that it is a debatable point whether DD streaks are "wiped away by winds"
or covered over by dust settlement?

Most likely the tracks have been covered up. As Doug stated in post #66, something happens during the winter that wipes out the DD tracks. As shown in by the quality in the Mcmurdo panorama, all weather related phenomena come to a stand-still during the winter. This allows the dust to settle and erase the tracks. Course when we add the recent dust storm into the equation its a whole new story.

By the way, the MRO images show a significant drop in albedo. How come Spirit did not notice this drop. Can we salvage the data to see this albedo drop through Spirit's eyes?

[Juramike]

Wow! This gets better and better!

It is interesting that some (not all, but some) dust devil tracks still go over the largest hills. Check out some of the tracks visible in the 1132-1089 differential image. So the hills seem a barrier to some of the dust devils.

Another thing interesting in the 1132-1089 differential image is seeing how many dust devil tracks originate in the area next to the crater just to the SW of the Columbia Hills. This is quite the little dust devil factory. What's up with that?

Looking at the largest crater in the NE corner, you can see small dark streaks were formed at sol 1132 that are just downwind of the lip of the crater. These slowly fade and reform in the downwind direction as the images progress. Are these streaks from little vortices that formed downwind at the dip of the crater? Could short downwind elevation drops explain the origin of dust devils as well?

I think this sequence shows some evidence of low constant overall dust deposition (erasing tracks), with localized darkening resulting from local mini-vortex/dust devil tracks. (Again, look at the crater in the NW and observe how the NE pointing short dark streaks appear to fade with time as well as the subjective observation that the "fresher" tracks appear darker.)

(You can also see some tracks crossing the crater floor)

Very cool sequence of images and differential images!

-Mike

[dvandorn]

Seeing as the conventional wisdom has it that the dust devil streaks are visible because the DDs sweep loose, bright dust from the ground, darkening it, then yes, it makes sense that the process of "erasing" the tracks is due to re-deposition of dust.

When I used the term "wipe," I was thinking more of how one wipes an Etch-A-Sketch clean, I suppose.

-the other Doug

[ElkGroveDan]

Dare I suggest that it is a debatable point whether DD streaks are "wiped away by winds"
or covered over by dust settlement?

What is known about particle movement in terrestrial dust devils, whirlwinds, tornadoes and other ground-contact atmospheric vortices suggests particle lifting and upward dispersion. So in short, no its not debatable.

[ilbasso]

A potentially good piece of news from these shots is that there are dust devil trails running along the north edge of Home Plate, not far from where Spirit is parked. I know we're leaving DD season, but let's keep our fingers crossed for more cleaning events.

[nprev]

Um...hate to broach this, but from previous discussions it appears that dust devils don't produce cleaning events; they seem to be caused by sustained conventional winds.

[centsworth_II]

...dust devils don't produce cleaning events...

You mean, dust devils haven't produced any cleaning events...yet. A dust
devil certainly would produce a rover cleaning event if it passed over the
rover.

[ilbasso]

I'm well aware of all of the past discussions. What I should have said is that anything - ANYTHING - that produces a gust of wind would be helpful for dear ol' Spirit these days!