Titan's topography, strange.... |
Titan's topography, strange.... |
Apr 12 2009, 12:44 PM
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#1
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Senior Member Group: Moderator Posts: 2785 Joined: 10-November 06 From: Pasadena, CA Member No.: 1345 |
Recent article in Science by Zebker et al.:
Zebker et al. Science in press, "Size and Shape of Saturn's Moon Titan". doi: 10.1126/science.1168905 (published online April 2, 2009) Link to abstract (pay-for article): http://www.sciencemag.org/cgi/content/abstract/1168905 Article on spaceref discusses this paper: http://www.spaceref.com/news/viewpr.html?pid=27912 Figure 3 from the Science article is a global elevation map relative to barycenter. Key points of article:
"Xanadu seems to be systematically lower than other parts of the equatorial belt, and not uplifted like most mountainous areas on Earth." (quote from Fig. 3 caption in article) -Mike -------------------- Some higher resolution images available at my photostream: http://www.flickr.com/photos/31678681@N07/
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Apr 15 2009, 07:17 PM
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#2
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Senior Member Group: Moderator Posts: 2785 Joined: 10-November 06 From: Pasadena, CA Member No.: 1345 |
The maps show the linear dune orientation. The linear dune orientation is based on the averaged wind vector. The alternating winds come from two different directions. These could be daily (tidal) or seasonal.
To make a linear dune, the alternating wind vectors need to be about 90 degrees apart or more. Looking at a linear dune, the averaged wind vector could be in either direction of the line. Looking at the forking pattern can determine which is the correct average direction. The GCM for Titan predicted an overall westerly course for the average winds on Titan (so average wind vector from the E). The observations show an average westerly vector for the surface winds. This is in contrast to the predicted GCM model (by Tokano et al.). Check out: http://www.astronomy.com/asy/default.aspx?c=a&id=7972 And you are correct, a typical sand particle will have a zig-zag path due to the alternating winds, but will run downcrest. If I understand it correctly, a strong wind from one of the alternating components could cause it the particle to "shift" it's path to the next dune set during it's zig-zag path (it zigs more than it zags). Thus the net sand flow could be off-angle to the dune crests. -------------------- Some higher resolution images available at my photostream: http://www.flickr.com/photos/31678681@N07/
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Apr 15 2009, 07:36 PM
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#3
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Senior Member Group: Members Posts: 3516 Joined: 4-November 05 From: North Wales Member No.: 542 |
To make a linear dune, the alternating wind vectors need to be about 90 degrees apart or more. Hope I'm not trying your patience, but this is the bit I don't quite get. What you say implies winds that blow, in general, at angles of 45 degrees or more to the equator. But this is not what Huygens observed, which was roughly E-W movement (parallel to the pair of nearby dunes), with reversals. It also seems at odds with the way we see clouds behaving, forming more or less latitudinal streaks. |
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