What are the Fastest Wind Speeds Observed on Mars?

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Kye Goodwin







PostPosted: October 1, 2005 12:53 PM 

I thought that this would be an easy question to answer, but so far I have not found a definitive source. On sol 214 in this list of Viking wind speeds, 25.9 m/sec (93.24 km/hr) was recorded.

[link]

I have seen second hand sources that claim a maximum for the Vikings of 30 m/sec (108 km/hr) achieved during a dust storm. The Pathfinder Lander recorded generally much lower wind speeds and a lower maximum. I have seen second hand sources that claim much higher wind speeds, up to several hundred kilometers per hour, but these have always been unreferenced. Perhaps these higher speeds were observed as the movement of weather systems as seen from orbit, or perhaps they have been calculated. Does anyone have a good reference on this topic?

Marz


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Reply: 1



PostPosted: October 1, 2005 1:51 PM 

Here's some more 2nd-hand references w/o bibliography:

[link]
"Typical wind speeds in the Martian atmosphere exceed 200 km/hr (or 125 miles/hr). Gusts can often reach 500 to 600 km/hr (or 300-375 miles/hr). Typical Wind speeds at the surface during a dust storm, as measured by the Viking landers, are typically about 30 m/sec (or 67.5 miles/hr). "

However, original sources are harder to come by:

Here's a link for Pathfinder data:
http://mpfwww.jpl.nasa.gov/MPF/science/lpsc98/1901.pdf

Max surface windspeed was 12 m/s

Kye Goodwin


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PostPosted: October 1, 2005 9:12 PM 

Thanks Marz, Yes, I have seen those very claims of very high wind speeds in other places. I wonder what the original source was? I can see that one might be able to measure large scale winds by following the movement of dust storms from orbit, but how could the speed of GUSTS be determined? Orbital radar? For the time being I think that wind speeds far higher than those measured by Viking are either theoretical or a rumour, but I am going to keep looking and would appreciate any leads.

Kye Goodwin


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Reply: 3



PostPosted: October 2, 2005 4:24 PM 

Google allowed me this snippet from a source that I cannot further access without subscribing. "The maximum wind speed measured by Viking 1. shortly after the onset of the second storm was 31 m/s."

I did not know until starting to research this topic, just how successful the Viking landers were in recording long-term weather data. They took observations for 3 1/2 Mars years each. Over this time there were 3 global dust storms, and the highest wind speeds were recorded during these events. I think that the maximum was probably 31 m/sec, 111.6 km/hr or about 70 mph. Here is an interesting graph of atmospheric pressure over the entire 3 1/2 years that shows the annual cycle and the timing of the storms.

[link]

I have also come across unreferenced assertions that those very high wind speeds that we have seen in secondary sources are based on out of date calculations that started with an inaccurate estimate of dust particle size.

Now my question is: What happened on the ground during those storms? Were sand-sized paticles moved or not?

Andy G


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Reply: 4



PostPosted: October 3, 2005 4:37 AM 

Hi Kye, re your reply 3.

Yes! Sand particles must move in weather like that. Given that:

Wind energy = 0.5 * density * v^3

A 31m/s wind on Mars (density = 0.02 kg/m3) generates almost 300 Watts per square metre. This is equivalent to 7.9 m/s (18 mph) winds on Earth (density 1.225 kg/m3) where sand would be blown about. Due to the reduced gravity on Mars, it'll be even easier to move sand particles in the Martian environment.

Andy G

Kye Goodwin


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PostPosted: October 3, 2005 11:51 AM 

Great theory Andy, but what was actually observed?

LaVache


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PostPosted: October 3, 2005 2:33 PM 

It's fact, Kye - high-school physics.

LaVache


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PostPosted: October 3, 2005 2:40 PM 

I make it 0.012 kg/m3 for Martian Atmosphere, Andy, although you may be making allowances for entrained solids. The dynamic viscosity is probably a more significant variable on Mars. Entrained solids on Earth are relatively insignificant due to the increased atmospheric density on Earth, however on Mars, they become a significant factor.

Kye Goodwin


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Reply: 8



PostPosted: October 3, 2005 6:01 PM 

LaVache, What was the wind speed at ground level when the wind speed at Viking's instrument was 31 m/sec? How tightly bound to the soil crusts are typical surface particles? How does the mix of particles available for movement affect saltation to reptation energy transfer?

I could go on. My point is that there is nothing like an observation. Knowing that coarse sand should in theory roll in Mars' wind, is never completely convincing, because the starting assumptions might turn out to be inaccurate when better observations come in. Seeing the before and after pictures from a dust storm would be a much better grade of "fact" than any theory. Also, I am asking a more complicated question: Does the Mars wind blow with enough energy to have placed the coarse-sand-sized duneform armour particles in their current positions? How about the spherules? This is a question that goes way beyond high-school physics. These systems are so complex that researchers still make regular use of wind-tunnels alongside theory.

Kye Goodwin


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PostPosted: October 3, 2005 6:23 PM 

LaVache, I'm sorry I was argumentative in that last post. If you or Andy understand this math and physics, I would really like to know all about it, with your help. Just what problem is it that you are solving and what starting assumptions are involved?

Kye Goodwin


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Reply: 10



PostPosted: October 3, 2005 7:37 PM 

Andy, LaVache, between your last posts I already have the answers to the questions that I posed in my last post, now that I have finally paid attention. Thanks, I see that because the wind energy is proportional to the cube of the velocity the effect of the low density of the atmosphere becomes less important as the wind speed increases.

I guess what I really want to know is just how close to the line does this come? Is it true, as Andy says, that sand MUST move?

If I correct Andy's calculation for the lower density that LaVache offered, I would have to guess a little less than 18 mph Earth equivalent (because I can't deal with that cube). I do not really know what that wind speed does to sand on Earth, but with the lower gravity I can see that it could well move coarse sand on Mars. Still, I think that with factors like a ground level wind speed possibly much lower than what Viking measured, and the effects of crusting, it is still not clear to me that significant coarse sand movement would take place. I will continue to investigate. Thanks.

Kye Goodwin


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Reply: 11



PostPosted: October 4, 2005 1:44 AM 

Here is a good reference without math on aeolian sand movement on Earth.

http://glamissanddunes.com/modules/sections/index.php?op=printpage&artid=4&PHPSESSID=5c8d1c3a5911e8c4f9455870a6a6781e

It states that the "fluid threshold" wind speed at which saltation begins to happen is about 10 to 20 miles/hour depending on grain size. Also, particles over about 1 mm diameter are saltated only by the strongest winds. There motion is more due to creep and is usually facilitated by smaller saltating particles colliding with them. The bedform armour particles are about 1 mm diameter and therefore would probably not move without in an Earth wind as slow as 18 mph. But with the effect of lower Mars gravity maybe they would move. I think that attempts to determine this theoretically are always going to be equivocal. I am back to trying to find those before and after pictures from Viking.

Andy G


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PostPosted: October 4, 2005 5:33 AM 

Hi LaVache...

I nabbed my density figure from the NASA Mars Fact Sheet, but the value does vary dependent on season and altitude.

With regards to the movement of sand particles, the evidence from the top of Husband Hill (extreme scouring on hard rocks) surely says that the process occurs.

Now, whether that is the result of once-per-year global sandstorms, summed over millenia, or the daily bump 'n' grind of standard aeolian movement is another matter.

Finally, with regards to wind action at the surface (as opposed to the situation up a Viking anemometer mast), wind tunnel experiments are extremely valuable due to their ability to model chaotic flow over irregular surfaces. In these instances, local and transitory wind speeds might well equal or exceed what you measure a few feet up in the air.

Andy G

Henry


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Reply: 13



PostPosted: October 4, 2005 1:01 PM 

Andy ( reply 4 ) :

I think I want to challenge the velocity-cubed relationship you suggest for drag on the Martian sand particles. Check out

[link]

For small particles, a linear dependence on wind velocity, and for larger objects a velocity-squared dependence is suggested.

But I’m hardly an expert. Do you have some references on the velocity-cubed as a sand-transport mechanism ?

Kye Goodwin


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Reply: 14



PostPosted: October 4, 2005 1:05 PM 

Andy G, I do not think that sand scour has caused the rough parallel ridges and troughs in the rocks at the summit of Husband Hill, but I do think that the ridges and troughs are aligned with the prevailing wind. The mechanism of their formation is related to wind, but we just do not know what it is. Remember that the formation of rock coatings is a major process at work on Mars.

The daily "bump'n'grind" is what we have been witnessing since the MERs landed, and it sure doesn't look capable of scouring rock, as only fluffy composite dust particles are moving.

While surface wind speeds can exceed those a metre above the surface this is the opposite of the expected and typically observed relationship.

Henry


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Reply: 15



PostPosted: October 4, 2005 1:36 PM 

http://www.magazine.noaa.gov/stories/images/sandstorm.gif

Little bit from NASA on sandstorms and dust storms, at

http://www.magazine.noaa.gov/stories/mag86.htm


Henry


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PostPosted: October 4, 2005 1:45 PM 

Another try at posting the image above:

http://www.magazine.noaa.gov/stories/images/sandstorm.gif

Kye Goodwin


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Reply: 17



PostPosted: October 5, 2005 12:59 PM 

Thanks Henry, I guess I am going to have to get into this math myself eventually if a want a theoretical answer to my question of whether or not sand is ever moved by wind on Mars. Like I have said before, though, I expect the theoretical answer to be too close to call in the end.

Now I have seen some second-hand references to dust-storm related changes to a pile of soil that Viking had excavated. I have read both that there was a lot of change and that there was almost no change over the course of the storm, so my search continues for the pictures or a detailed, reliable account of what they revealed.

Henry


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Reply: 18



PostPosted: October 5, 2005 2:16 PM 

Yes, Kye, the theoretical predictions of wind-driven sand are pretty complicated, as witnessed by this article:

http://www.arl.noaa.gov/ss/transport/dust/duststorm.pdf

Flow, in general, is pretty complicated. The physicist Heisenberg ( of Uncertainty Principle fame ) started his career in hydrodynamics, but soon moved on into Quantum Mechanics, having been heard to say, “There must be an easier way to make a living…”.

hortonheardawho


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Reply: 19



PostPosted: October 5, 2005 4:48 PM 

One of the reasons I have not jumped on the "microchannels are water / brine flowing features" band wagon is the fact that fluid flows with suspended particles are notoriously "non-Neutonian" -- which basicly means non-linear -- which practically means calculationally difficult -- which really means no "intuitive" observational parameters.

Here's a sample question:

Could dust laden wind alone be responsible for lifting a block of etched terrain pavement?

If we saw this bump in the road on a salt flat on Earth, what would be the suspected geological process? Are the microchannels nearby a clue?

Here is the full view.

Beats me.

*** remaining post is personal and may be ignored:

For the curious about how I know something about non-Neutonian flow, I had occasion many decades ago to be involved in creating a 3D, 3 phase model of the flow of bitumen in the Alberta Tar sands. It was the most complex physical modelling program I ever wrote and at the time was one of the few such models in the world.

Ah, those were the good old days...

Why, when I was a boy ... big iron was the only way to solve these problems.

You guys simply don't know what you missed.

LaVache


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Reply: 20



PostPosted: October 5, 2005 8:45 PM 

Henry (Reply 13), Energy and force are two different things. For force, the variation is linear for acceleration or proportional to the square of the velocity, whereas for energy, Wind energy = 0.5 * density * v^3 as Andy pointed out, although strictly speaking this refers to specific wind turbine energy transfers. Kinetic energy is generally proportional to the 0.5mv^2. - Also momentum is linear.

Effectively the power of abrasion is related to the mass and the square of the velocity of flying sand particles. The sand particle velocity should approach the wind velocity, even on Mars, so that the energy transfer with the higher wind velocity may result in higher abrasional power than for Earth based sandstorms.

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