The Storm, Dust storm of 2007 Options

[Tman]

BTW the red tag continues to confuse me. They just look like a lot of number to me.

This site on the MER homepage explains the whole image code.

[helvick]

That 255 whr figure for Sol 1225 is bugging me (Sorry Astr0 - feel free to object right back )

I calculate that at a Tau of 4.1 on Sol 1225 for Opportunity she should have generated around 310Whr.

All of the other numbers that I've seen recently indicate that the insolation model I'm using underestimates the real values by 10% or so ( e.g. on sol 1221 @ Tau=3.3 the MER team have published a value of 402 Whr when I estimated about 360 Whr ). That would make me expect a real value of about 340 Whr if the Tau value of 4.1 is correct. Furthermore I really suspect that there was at least one small (5% or so) cleaning event sometime between Sol 1211 and 1220 which would put the number closer to 355Whr.

The most likely reason for this is that the diffuse Insolation model I'm using becomes increasingly unreliable as Tau rises past ~3 but it is also possible that the 255 Whr number isn't accurate. I'm also very surprised at Opportunity being able to function at all at that level, my understanding all along has been that 270-280Whr is extremely marginal for her given her stuck heater.

Very much looking forward to published numbers from the team.

[Floyd]

BTW the red tag continues to confuse me. They just look like a lot of number to me.

The code is explained here.

Edit: sorry didn't see Tman's post as was reading the previous page.

[fredk]

That 255 whr figure for Sol 1225 is bugging me

Well, we had that report that began this thread that the direct sun was attenuated by "nearly 99%" (tau = 4.6), with power at 280 Whr. The report was dated the 5th (sol 1225), though the sol is not mentioned in the article. Does that fit your model better?

The more recent data show a peak at 4.1, so 4.6 seems to have been an error. I suppose at times like this with everyone wanting tau values, numbers get out that aren't very accurate. Let's hope the clearing trend continues!

[hendric]

Is it possible that the Tau reading is just a single point on a line, ie the Tau could be 4.6 now, but could be lower or higher before and after that reading. Tau comes from looking at the sun, right? So power produced could be slightly off from what you expect because the dust isn't consistent either across the sky, or from morning to evening.

[edstrick]

high dust opacity drops daytime temperatures, but raises nighttime temperatures.

Local dust storms, if strong, show strongly convecting or at least dynamically churning clouds, often with some mixed-in condensation clouds, as seen from orbit. They can probably be quite opaque, but then the dust spreads out and disperses, like the storm that happened shortly before Beagle and MER's arrived.

Globe-encercling storms have been observed from orbit in development phase 3 times (2 viking orbiter storms and the 2001 storm), and once in the decay phase (the greatest of all, the 1971 global storm: Mariner 9.) Storm heating probably has a massive "ripple" effect on the adjacent atmosphere, as well as strongly boosting global atmospheric thermally-driven tidal oscillations, and can probably cause unusually strong winds even in non-storm-dust affected areas before the dust arrives. Areas near an active storm may plausibly have such strong induced winds that there is strong local dust scouring and lifting, causing a propagation of the main storm, starting solar heating of the newly raised dust in a sort of chain-reaction effect.

We just don't really understand the meteorology of storms and their growth. Vikings got some good photography at intervals, as well as infrared thermal mapper data. The 2001 storm was before Odyssey's arrival, I think but had good coverage by MGS's wide angle cameras and the thermal infrared spectrometer. With the wide angle cam on recon orbiter and the climate sounder, we're getting our first meteorology instrument look at a big storm :-) I hope to hell the've switched the instrument back into scanning mode for the storm.

[Pertinax]

Is it possible that the Tau reading is just a single point on a line, ie the Tau could be 4.6 now, but could be lower or higher before and after that reading. Tau comes from looking at the sun, right? So power produced could be slightly off from what you expect because the dust isn't consistent either across the sky, or from morning to evening.

I would be strongly suspicious of any answer other than 'absolutely'.

The dust in the atmosphere certainly varies on short time scales -- they do on earth. Also, as you noted the extinction of sunlight would be greater for lower sun angles than higher for any given tau, as the effective optical depth increases with a lower sun (sun having to shine though a greater volume of air & dust). I have wondered myself how for a constant tau the sky appearance (including of course scattered light) would vary.

FWIW: http://marswatch.astro.cornell.edu/Bell_etal_SkyColor_06.pdf

-- Pertinax

[helvick]

Thanks for the input folks.
The MER team's Tau values into account the solar zenith angle and the resulting increase in air mass as do my calculations for beam insolation. You can see this in the published Tau charts - the air mass numbers and DN's vary as they should with the changes in the local true solar time of the Pancam shots the readings are based on and the resulting Tau values are pretty consistent throughout each sol (on the occassions that multiple readings are taken)

However even though they are consistent there is definitely a daily cycle - Tau (generally) increases slightly over the course of a normal sol and then clears up slightly again overnight. Whether this cycle is more or less pronounced during a storm I can't say but for the vast majority of the year the variation is <0.1 over the course of each sol. To explain the variation I'm puzzled by we would need a variation of about 2.0 for about half the sol.

It is probable that part of the explanation is that very short time scale events (passing higher density dust flurries for example) are causing significant variations in Tau during the day.

[Pertinax]

For fun, a question that I can probably dig for an answer for if there is not a quick one available here.....

Question: Is there engineering data available from the rovers (in the PDS I would presume) which reports the output from the solar arrays? If so, what is the temporal resolution (and averaging period if any) of the data?

It would be fascinating data if available in decent resolution.


-- Pertinax

[climber]

I was wondering if we have, here on Earth, the equivalent of Marsian's dust storms?
For exemple, dusts coming from deserts that goes very high in our atmosphere where the pressure could be comparable to what it is on Mars?

[helvick]

Pertinax wrote: It would be fascinating data if available in decent resolution.

I've been saying that for years.

I don't think we'll see it any time soon unfortunately. It's engineering data that doesn't directly feed into any science data (as far as I know) and since some of the engineering data skirts into ITAR terrain releasing any of it requires that lawyers clear it first. That's just asking too much for data that is only of marginal interest at this stage in the mission. It would be great if someone used the data as part of a paper (say on short time scale variations in atmospheric opacity) and got it published that way,

The temporal resolution was good enough for the team to be able to specify that Spirit's last major cleaning event happened at 13:20 local time (IIRC) so I think it's at least possible to get it down to 10 minute intervals.

[tty]

I was wondering if we have, here on Earth, the equivalent of Marsian's dust storms?
For exemple, dusts coming from deserts that goes very high in our atmosphere where the pressure could be comparable to what it is on Mars?

Desert dust certainly can spread quite far. For example a fair amount of the soil on Bermuda is very fine saharan dust accumulated over hundreds of thousands of years. However terran "weather" in almost all forms very largely happens in the troposphere. For example despite the vast amount of salt spray created continuously over the oceans essentially nothing gets into the stratosphere (otherwise the sky at twilight would be yellow from the Na and the ozone layer would be destroyed by the Cl).

About the only exceptions is material from volcanic eruptions and large impacts which gets injected into the stratosphere with consequent climate effects extending over years (dust in the troposhere is washed out by rain fairly quickly).

[djellison]

Saharan dust landing on cars in the UK isn't uncommon - I remeber two distinct occurances of that in the past decade or so.
Meanwhile - updated to 1230/1250 actual figures

Massive kudos to Mark for putting these on line so quickly.

Attached thumbnail(s)

 

[Guest_Oersted_*]

The Sirocco:

Some nice pics here of the dust blowing from the Sahara up towards Europe.

http://en.wikipedia.org/wiki/Sirocco

[djellison]

Infact -thinking about it - I remember finding comedy in the fact that a Sirocco was dumping sand on my mums VW Sirocco.

Doug