Clouds, Clouds over Victoria |
Clouds, Clouds over Victoria |
Oct 9 2006, 11:46 AM
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Senior Member Group: Members Posts: 2820 Joined: 22-April 05 From: Ridderkerk, Netherlands Member No.: 353 |
With the images of clouds coming down, it is time for a new thread.
Here is just part of a panorama. Autostitch was not able to stitch more than those 2 images of 4 images. I think because there are not enough matching points. Maybe one of the other programms can do it better? Taken with the L0 navcam on Sol 962. jvandriel EDIT. I have done my math again and the Sol is not Sol 962 but Sol 950. I know there is a little program for finding the right Sol but i can't find it. jvandriel |
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Guest_Myran_* |
Oct 25 2006, 08:02 PM
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#2
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Guests |
QUOTE elakdawalla wrote: I always thought it precipitated in place but there are lots of researchers using the word "snow" so now I'm really confused. Anybody have any insight? Well I dont have any real insight, but I have always thought that the 'snow' imagined by Viking actually was hoarfrost. |
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Oct 25 2006, 09:59 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 |
Well I dont have any real insight, but I have always thought that the 'snow' imagined by Viking actually was hoarfrost. Hoarfrost implies saturated air at the surface. Clouds imply saturated air at altitude. Opponents of 'snow' seem to be saying there must always be an unsaturated layer in between where descending ice particles would sublime. I don't see why. |
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Oct 26 2006, 04:00 PM
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#4
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Member Group: Members Posts: 156 Joined: 18-March 05 From: Germany Member No.: 211 |
Hoarfrost implies saturated air at the surface. Clouds imply saturated air at altitude. Opponents of 'snow' seem to be saying there must always be an unsaturated layer in between where descending ice particles would sublime. I don't see why. If the current vapor pressure was equal to the saturation vapor pressure throughout the atmosphere you'd have very thick clouds (somthing like nimbostratus on Earth, at least you'd have more clouds than are observed at lower altitudes). And there aren't any, that is what we see. Thus, the water vapor pressure is lower than the saturation vapor pressure below the martian clouds. Therefore, any ice crystals that fall down would sublime long before they'd reach the surface. On Earth there are situations where falling precipitation (snow) does not reach the surface, too, because the air layer below is very dry. As the falling snow evaporates/sublimes, the underlying air gets enriched with water vapor until the saturation vapor pressure is reached. So, consecutively, the snow can reach lower altitudes until the whole airmass below the clouds is very moist and the snow reaches the surface. That only works well if the dewpoint is below 0°C between the clouds and the surface (otherwise the air mass does not get cooled below 0°C and the snow melts). That just happened in Denver, CO. Yesterday they had 17°C, but the dewpoint was very low (<0°C) below the clouds. And today you have snow in Denver and temperatures around 0°C. That resulted from the process described above. Such a process could not occur on Mars under current atmospheric conditions as you need *a lot of snow* = thick clouds to moisten the whole layer of air below the snow producing clouds. There simply isn't enough water vapor. Michael |
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Oct 26 2006, 04:37 PM
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#5
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Senior Member Group: Members Posts: 3516 Joined: 4-November 05 From: North Wales Member No.: 542 |
If the current vapor pressure was equal to the saturation vapor pressure throughout the atmosphere you'd have very thick clouds (somthing like nimbostratus on Earth, at least you'd have more clouds than are observed at lower altitudes). And there aren't any, that is what we see. Thus, the water vapor pressure is lower than the saturation vapor pressure below the martian clouds. Therefore, any ice crystals that fall down would sublime long before they'd reach the surface. Sure, that's what we see in the daytime. But in the middle of a polar winter night? |
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Oct 26 2006, 06:13 PM
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Member Group: Members Posts: 156 Joined: 18-March 05 From: Germany Member No.: 211 |
Sure, that's what we see in the daytime. But in the middle of a polar winter night? Yes, that is certainly true. I remember now that I read a publication by some french scientists who modelled clouds induced by orography over the north polar regions (observed through MOLA?). These clouds were made of dry ice particles (CO2). I think they wrote something about possible small amounts of precipitation from these clouds, but CO2-ice crystals, not water. Can't find that publication any more, unfortunately. Michael |
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