the picture I tried to link to above:

An amazing picture, when you inspect the crater bottom. Obviously Mars, but where?

Here's a thought - under certain conditions winds can create "standing waves" upwards in air which become visible as linear ripple clouds. Could the same effect operate downwards into an enclosed depression like Victoria, and create ripples in the dust? Australia's Morning Glory is one, and the initial large cloud is often followed by subsequent parallel crests of cloud interspersed with clear air.

http://www.cloudappreciationsociety.org/a/glory/glory1.html

http://www.greenhorsesociety.com/Clouds/Glory.htm

At sea, of course, steadily blowing winds raise ripples in the form of sea swells, manifested in regular ripple crests.

Kenny

Just so. At sea travelling waves. On a small pond or birdbath standing waves. But this is reasoning by analogy - it's not so easy to understand the actual mechanism for the sand dune case.

Also consider that the sediment in the bottom of Victoria is probably not sand, but finer-grained particles which may carry an electrostatic charge.

Great photo. Thanks. Perhaps a HiRise candidate? Is there a higher resolution version?

Sorry, I've no idea where the image came from - I found it by chance on a maths website. I expect many similar examples will come from HiRISE (perhaps there are even some already).

OK folks, eye strain time. Here is a long baseline colour anaglyph of the Victoria dune field. The baseline is a bit long really and the repetitive and low contrast nature of the dunes make this a little tricky.

I'm going to upload three scaled versions. The full resolution one is great for viewing the dunes on the left (which are stunning!), but I find the right side very difficult. In the half resolution version it is much easier. I've also included a small quarter scale one which is good for seeing the whole dune field at once.

Full res version - start by looking at the dunes 1/3 of the way from the left.


Half res.


Quarter res.


Enjoy,

James

Thanks James.

Hmmm...is the melange scoop on Oppy's arm functional? Might need it in there!

Andy

If they are forming reipples and dunes then the particles composing them must have been transported and deposited as sand sized grains. Of course, they may (or may not) consist of electrostatically bound aggregates, but these are still functionally sand grains.

Jon

When I used the term 'sand', I was simply referring to the size of the grains. The standard scale that I had in mind classifies sand-sized grains as those particles whose diameter is between 2mm and 1/16 mm. Grains between 1/16 mm and 1/256 mm are called silt-sized grains. The smallest grain sizes fall into the clay size range.
Certainly the sediments composing the drifts in the bottom of Victoria were transported as a bedload, via saltation or perhaps as very low-level suspended load. All I meant by my comment was that the finer grain sizes may behave differently than the sand-sized grains, and that terrestrial sand dunes might not provide the perfect analogy for the martian drifts. There may be some important similarities, between the two types of deposits, but there may be some significant differences.
Those differences could make the origin of the martian drifts that much more difficult to decipher.

After writing all this I vaguely remember a discussion some time ago about how the different grains sizes behave in the less dense atmopshere and lower gravity of Mars ... but the wheels of my memory these days are turning about as fast as spirit's right front wheel...

That's one rough washboard! They work great for me, but then I can contort my eyes pretty much any which way.

While different atmospheric density and gravity have an infuence, the difference between sand forming dunes and other bedforms and finer particles forming mantling deposits of parna still hold true - AFAIK.

Jon

I think the difference is grain/particle size. Martian "sand" probably fits mostly into the silt or clay terrestrial categories. You'd never get it out of your spacesuit if you rolled in it! Note to future Marsonauts. Bring lots of wet wipes.

http://www.agu.org/cgi-bin/wais?dd=H31G-02

Thanks for the link, Mark. That helped clear up a few of my questions.

Please note that the linked abstracts says:

However, recent field evidence collected by MER is inconsistent with these predictions, revealing well-formed, active ripples of 100 micron basaltic sand

If we see ripples or dunes or dunes on Mars then they are composed of sand sized particles, just as they are Earth. Finer particles will not form ripples or dunes, instead they will form coatings and mantles, again, just as they do here.

As far as space suits go, the ease with which the rovers are cleaned by wind gusts suggests that cleaning of future suits will not be a problem. Brushes, compressed air jets, small vacuum cleaners should suffice.

Jon