Bendy winds?
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wassock
moderator
Seems to me that the wind on the far right blows in a curved stylie http://hirise-pds.lpl.arizona.edu/PDS/EXTRAS/RDR/ESP/ORB_029900_029999/ESP_029934_0935/ESP_029934_0935_RED.abrowse.jpg
AND ~ perpendicular to the rest of the image!
Posted
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wassock
moderator
Another example, curves on the left and right end fans in a markedly different direction to the middle http://hirise-pds.lpl.arizona.edu/PDS/EXTRAS/RDR/ESP/ORB_013000_013099/ESP_013095_0935/ESP_013095_0935_RED.abrowse.jpg
These two images both show the same area first 14 Dec 12 2nd 12 May 09
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wassock
moderator
One more, same area 21Jan 09 http://hirise-pds.lpl.arizona.edu/PDS/EXTRAS/RDR/ESP/ORB_011600_011699/ESP_011671_0935/ESP_011671_0935_RED.abrowse.jpg
Could these images be showing a snapshot of cyclonic weather systems, are they something to-do with topography, or are the eruptions synching nicely with a changing wind?
In the two 09 pics the same groups of divergent fans can be seen still holding much the same directions in both -to my eye anyway
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Kitharode
moderator
Woweee ... That's awesome. Can't answer any of your questions but, yes, how can it be anything other than 'curved wind'?
Direction of light please? Assuming from lower right, but there's a lot going on so...... Like the cyclonic idea a lot.
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Kitharode
moderator
Definately a 'flat' image is it? No map projection, stretchy, lens flare thingy at play then? Just a thought.
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wassock
moderator
in response to Kitharode's comment.
Just checked and it is actually the same area as discussed in the paper you put up on "crater?"
So it is map projected and the slope runs sort of diagonally from the bottom corner to the top corner
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wassock
moderator
in response to Kitharode's comment.
Alternative explanation would be that the fans are mostly caused by the slope. If the plume emits perpendicular to the slope then it will settle to the downslope side maybe? But there are some side fans so wind must be a factor.
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Kitharode
moderator
Well done on putting the image and the "crater" paper together. This 'slope' factor is popping up more and more, don't you think? Undoubtably wind involved, but introducing slope and wind combined is interesting. Cound imagine all sorts of scenarios popping up from that. Hope you crack this one, could be useful all round.
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wassock
moderator
Would appear not to happen every year 2010 November here http://hirise-pds.lpl.arizona.edu/PDS/EXTRAS/RDR/ESP/ORB_020300_020399/ESP_020321_0935/ESP_020321_0935_RED.browse.jpg
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Kitharode
moderator
Curiouser and curiouser .. what will you find next? Somebody else just mentioned 'contours' crossing their mind when they saw this. (As usual can't remember where). I'm following....
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JellyMonster
in response to Kitharode's comment.
Somebody else just mentioned 'contours' crossing their mind when they saw this.
Not this then?... http://talk.planetfour.org/#/collections/CPFL00000b
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wassock
moderator
That one is different JM the sources of the fans follow a curve, in my ones there are lines of fans which when viewed from afar follow a curve. Apols if you knew that
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Kitharode
moderator
in response to JellyMonster's comment.
JM. Only getting a blank page via link, but it must be my end if wassock sees it. I can guess what he's saying though, I've got a few 'curved lines' of fans myself. Definately vents in a curve there, but wind/slope'contour in wassocks image.
Just remembered it was DrTechnician who mentioned contour, in a pm recently. Nice bloke, does ICT, seems interested in 'digital wizardry', say hello if you see him.
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wassock
moderator
Kith the CPF bit of the URL is detached from the rest of it so there are two links in the post. Just click on the end bit
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wassock
moderator
in response to wassock's comment.
6 Oct 12 not much wind and no real variability in direction http://hirise-pds.lpl.arizona.edu/PDS/EXTRAS/RDR/ESP/ORB_029000_029099/ESP_029037_0935/ESP_029037_0935_RED.abrowse.jpg
23 Nov 12 lots of directions http://hirise-pds.lpl.arizona.edu/PDS/EXTRAS/RDR/ESP/ORB_029600_029699/ESP_029657_0935/ESP_029657_0935_RED.abrowse.jpg
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Kitharode
moderator
in response to wassock's comment.
Cheers wassock. Met them before and keep forgetting about it. Techno stuff - does my head in * :-X *
What's CPF?
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wassock
moderator
in response to Kitharode's comment.
As in CPFL00000b
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Kitharode
moderator
"Cannot Picture Find" methinks. (Got it now, thanks).
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Kitharode
moderator
Your original 'cyclonic winds' idea, for your original image, is still open to debate methinks. Wind must play its part if multiple fans are involved (I think). But I'm getting a better understanding now for the importance of slope, even when minimal, to affect fan alignments. This in particular is impressive. Check out the 'river' in the bottom right corner. http://hirise-pds.lpl.arizona.edu/PDS/EXTRAS/RDR/ESP/ORB_011900_011999/ESP_011900_0985/ESP_011900_0985_RED.browse.jpg
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Kitharode
moderator
Also regarding previous image, why are most of the fans in depressed (shaded) areas? Is it because they were warmed earlier in the day before the Sun moved round to current position, perhaps acting as sun traps? Is there any venting involved in this scenario, or is it all 'leakage' creeping downslope?
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wassock
moderator
Now that's a good one. I don't see anything with big directional fans so inclined to go with slope induced for now. The bits with few fans seem to be at the tops of slopes maybe the ice presses closer there?
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mschwamb
scientist, translator
in response to Kitharode's comment.
That's very much what we think is happening. Pommerol et al 2011 have a nice graphic. See below:
It's also been found that fans and spider channels seem to follow local topography which also may be due to the geysers not going very high and the very bottom layer of winds pushing the material brought up from below the ice sheet.
Cheers,
~Meg
Posted
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wassock
moderator
in response to mschwamb's comment.
Meg that's OK for blotches an fans showing one direction, downslope, but what happens when the wind blows. If the terrain influences the shape when no wind it should continue to affect the shape when the wind blows. Hence where there is a terrain effect and we get several separate fans they should all have a different shape. I'm not seeing that in the images.
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mschwamb
scientist, translator
in response to wassock's comment.
I can't comment well on this, so I'm speculating on the top of my head on what I remember reading. By terrain effect, my understanding it's direction pointing so that all the fans point downhill, which you'd also expect from blowing down the sides of a crater or around a raised area. So it's more of a how the wind is blowing around obstacles and such. I'm not sure we could fully separate out a wind from terrain thing completely in terms of shape of the fan. I also believe it's been measured that the spider channels change width going uphill/downhill.
Cheers,
~Meg
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wassock
moderator
in response to mschwamb's comment.
Think the theory is that spider channels are observed to widen as they go uphill which evidences them as product of gas rather than liquid erosion.
The basic model for fan formation seems to be a jet coming out at a reasonable pressure to produce a plume. There's modeling in one of the papers using an angled plume to give a classic fan under still air conditions. If the plume is vertical then the fan will look the same which ever way the wind blows. If a fan is not vertical then the shape of the fan will alter as the wing changes. In a fanfield where each vent shows several fans in different directions but all having pretty much h the same shape then ALL the vents must be producing a vertical plume. Even on flat terrain this would seem unlikely, more so on a slope . Thus the ballistic directional idea of a vent/plume may not hold for these fans, but a low pressure thermally driven venting would work maybe
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mschwamb
scientist, translator
in response to wassock's comment.
My reading was the ballistic model in paper was using average wind estimates for Mars, but they may only be during the discussion of particle size. My understanding was that in still air conditions you'd form a blotch, or at least that's what I've heard from other members of the science team. So I'm not sure if your argument still holds then.
I believe this is something that can be explored further with the classifications of the blotches and fans. So that's why we really do want people to mark and map all the fans and blotches in the image because quantity is going to be needed to assess that.
Cheers,
~Meg
Posted
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wassock
moderator
in response to mschwamb's comment.
The model I am looking at (paper II Thomas et al) has a vent on a 20 degree slope with the plume normal to the surface. Nothing about wind speed. Thus in still air this angled vent gives a fan, a straight up plume would give a round blotch in still air.
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mschwamb
scientist, translator
in response to wassock's comment.
The 2011 Thomas paper (Sub‐surface CO2 gas flow in Mars’ polar regions: Gas transport under constant production rate conditions) has wind included - "Model 508 was an attempt to test extreme conditions by quadrupling the gas production rate, increasing the length of the tube to 1 m, and increasing the wind velocity to 3 m/s." The 2010 ballistic approach does not include wind, but not everything is sloped, so the ballistic approach can't be completely right. On slopes I think you're right this will have some impact and probably produce less blotches (we should be able to test that with the classifications from Planet Four).
My understanding from conversations with Candy and the rest of the science team is that blotches are thought to be produced when there is no wind. Slopes does play a factor as you point out, and will produce fans if the geyser is angled.
Cheers,
~MegPosted
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wassock
moderator
in response to mschwamb's comment.
OK so a ballistic vent will produce a fan if it is non vertical, more angle better defined fan. A ballistic fan straight up on a flat surface gives blotch in still air and a fan if there is a wind and the shape of the fan for different wind directions will be the same ,depending on wind speed, and similar shape to the ballistic angled one.
So for a fan field on a slope in still air we get downhill fans if the plumes are normal to the surface if the wind blows across the plume then the resultant fan will be deformed. If all the plumes come out vertically then slope can play no part and the plumes will look the same which ever way the wind blows.
So what do we observe? We have multi fan fields with large numbers of vents each with several fans in different directions all sowing the same basic shapes. In other areas we have fans which do not all point the same way and this can be explained as the effect of local topography But the same areas also sometimes have fans which do not follow the lie of the land but still have the standard shape. But for the fans to follow the slope they must be angled and a wind in any direction not in line with the fan must deform it. Is there any reason to suppose that vents will always erupt vertically? If not then even on the flat some vents should produce fans in still air and the shape of successive fans will vary according to wind direction.
Seems to me that if plumes are ballistic they must always erupt vertically to explain the patterns of fans we see, except where they form fans following the slope when they erupt at an angle that is directional, but I've not seen anything which I could call such a fan distorted by a cross wind. This is inconsistent and It would seem that the theory cannot have it both ways.
I probably need to draw some pictures to better get this across but it seems to me that the ballistic plume model has no right to always produce a vertical plume, if some plumes are angled then the multidirection fans we see don't make sense.
But low pressure thermal venting would always produce a vertical plume in still air and could explain the fan shapes.Posted
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mschwamb
scientist, translator
in response to wassock's comment.
These are all good questions. I'm not an expert on the physics of the outgassing events, so I can't answer them. Other members of the team who model this would be better suited to chime in here.
I think there are many factors that will contribute to the fans so the ballistic approach is a good starting point but is simplified because it doesn't take into account atmospheric drag and turbulence. Also particle size sorting may be happening as well. In terms of widths, it's been observed in previous HiRISE images that fans have changed direction which indicate changing wind direction, so if there was north east wind in the morning and a north west in the afternoon that would impact fan shape in a particular region.
I think many of things you are saying require the measurements from Planet Four to really answer. There isn't a large number measurement of the fan widths. Planet Four would provide the first from my understanding. Also with so many fans marked, once directions are obtained the science team wants to compare to Mars Global Climate models which simulate the current Martian climate and produce a synthetic wind map to compare to the measured fan directions and blotch locations on the South Pole.
Lot of things that we can look once at we have such a large sample of fan lengths, widths, and directions. That's why it's really to important to map as many fans and blotches as possible that you see in the images.
Cheers,
~Meg
Posted
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wassock
moderator
in response to mschwamb's comment.
And another thing.....
This image shows several 'bunches' of fans each coming from a common source. There are mostly 4 main fans in each bunch and to a casual glance the relative proportions of each bunch seems to be consistent and the individual fans in each bunch are all symmetrical about their own axis.
If the plume producing these fans is ballistic in nature then each one must be vertical with respect to the wind direction which has produced each discrete fan, as all share the same basic shape and symmetry. If the surface is sloped then this means that (all) the vents are non-normal to the surface.The consistency of the relative sizes of the fans in each bunch (if true) must be telling us something about the mechanism producing the plumes. Essentially the properties of each plume, height, velocity, particulate content, duration, must maintain the proportionality as those around it. So if the first eruption at point 1 produces a fan 100 metres long and the fan next to it is 50 meters. Then on the next eruption fan 1 is 50 metres (in a different direction to the first time) the the corresponding fan at the other vent is only 25 meters. And this appears to hold true for a large numbers of vents across a large area of the surface.
I can see two immediate ideas for how this would work. All the vents could be connected to the same under ice resevoir of gas and would take proportionately the same fraction from it at each eruption. Or there is a very simple set of parameters which control how much gas is evolved at each vent, something like amount of sunshine times the area each vent collects gas from, which would mean that the size of the eruption at each vent remained proportionally constant.
Neither of these work too well with the "the vent seals, pressure builds up, and then the vent bursts again" idea, mainly because it seems unlikely that all the vents in a large field could be made to seal and pop in a synchronised manner and so a constant out gassing driven by the sun each day would appear to be a better theory to explain the observed patterns.
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Kitharode
moderator
Don't know if you've already seen it, but "constant outgassing" is mentioned in one of the science papers. Can't remember which one, or whether it is mentioned in detail or in passing.
Posted
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mschwamb
scientist, translator
in response to wassock's comment.
The other question is what is the time frame for the formation of the multiple fans originating from the same source. is it over hours which might suggest it's mainly the wind direction changing. I am not sure that all those geysers are interconnected under the ice sheet, but I agree that the we can test the "very simple set of parameters which control how much gas is evolved at each vent, something like amount of sunshine times the area each vent collects gas from" by looking at the widths, angles, and lengths from year to year and throughout a season.
Also looking at total area covered by the fans and blotches should give some estimate of the total amount of material uplifted which might be able to give an estimate of the total amount of carbon dioxide gas required to entrain the dust.
Cheers,
~MegPosted
