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Dust Storm
Tom Dahl
post Jul 12 2018, 04:03 PM
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Wow, an amazing image to have captured yourself!
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JRehling
post Jul 13 2018, 03:42 AM
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Thanks! I wish the dust storm had not been in the way, and I know that many others feel the same. Perhaps it will fade soon.
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marsophile
post Jul 15 2018, 01:28 AM
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Hmm. Although the seasonal upward trend is similar, the pressure during this dust storm, as measured by REMS, is about 20 pascals lower than at a similar period during the last three Martian years.

Pressure (pascals) for LS 198-208:
2018 779-807

2016 798-823
2014 802-829
2012 805-830

Sources:
https://mars.nasa.gov/msl/mission/instrumen...onsensors/rems/
https://github.com/the-pudding/data/blob/ma...ars-weather.csv
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serpens
post Jul 15 2018, 06:33 AM
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I wouldn't read too much into this. The Gale crater temperature/pressure during the course of a sol is governed by the crater topography so that during the day as temperature increases atmosphere flows out of the crater reducing the air pressure while at night colder air settles into the crater from the rim. The drop in upper atmosphere temperatures and increase in lower atmosphere temperatures due to the dust storm has probably had an effect on this cycle.
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marsophile
post Jul 15 2018, 06:08 PM
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The lower pressure this Mars year seems to have preceded the dust storm by several months.
For example at LS 135:

2018 727

2016 747
2014 750
2012 N/A

The 2018 LS 135 was on 02-27. Perhaps an overall lower pressure is predictive of the year in which a major dust storm is likely to occur?
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mcaplinger
post Jul 15 2018, 11:31 PM
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QUOTE (marsophile @ Jul 15 2018, 10:08 AM) *
The lower pressure this Mars year seems to have preceded the dust storm by several months.

According to http://cab.inta-csic.es/rems/wp-content/up...RATION_PLAN.pdf the pressure sensor is only required to be accurate to 10 Pa at beginning of life and 20 Pa at end of life (end of the primary mission, I presume.) It may be doing better than that, but I'd be reluctant to draw any conclusions from absolute pressure measurements over long time scales without taking possible instrument drift into account.


--------------------
Disclaimer: This post is based on public information only. Any opinions are my own.
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marsophile
post Jul 17 2018, 01:44 AM
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QUOTE (mcaplinger @ Jul 15 2018, 03:31 PM) *
I'd be reluctant to draw any conclusions from absolute pressure measurements over long time scales without taking possible instrument drift into account.

Good point! Based on your comment I took a look at when the larger pressure differential occurred.

Earth_date ls month pressure

2017-08-18 048 Month 2 881
2015-10-01 048 Month 2 901

2016-09-12 220 Month 8 859
2014-10-24 220 Month 8 862

The deficit in pressure from the previous year seems to have gradually widened over a period of about a half Martian year, and to have stayed roughly constant since then. This could be consistent with instrument drift. It will be interesting to see where it goes from here. It's a pity there is no ongoing way of calibrating the instrument.
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JRehling
post Jul 17 2018, 01:56 AM
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Can radio occultation measurements from orbiters be used to measure pressure? That was how atmospheric density was measured in many other cases in the past, e.g., Voyager 1 and Titan.
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Deimos
post Jul 17 2018, 04:31 AM
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The interpretation of the pressure differences above might be different if the altitude change were considered: ~225 m in the Ls 48 comparison, but only ~89 m in the Ls 220 comparison. One would expect a more than 2% drop in the first case (little residual), but <1% in the second (residual increases slightly with time between those two specific points). Given the possibility for drift, interpreting any residual variation seems sporty.
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marsophile
post Jul 17 2018, 04:12 PM
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Just saw what looked like a brief downllink from Opportunity on DSN Now:

DOWN SIGNAL

SOURCE
OPPORTUNITY

TYPE
CARRIER

DATA RATE
1.10 Mb/sec

FREQUENCY

8.45 GHz

[EDIT: Now it is showing MAVEN as the source with similar data rate and frequency. Maybe it was some kind of switch-over glitch.]
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djellison
post Jul 17 2018, 05:13 PM
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You will regularly see very brief appearances of Opportunity 'locking up' briefly.

It's usually side bands from MRO, and less frequently MAVEN drifting thru the frequency we're looking at - and the receiver incorrectly locking up on it. We have to manually drop lock and then carry on looking - so briefly, it appears Opportunity is transmitting when it isn't.
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marsophile
post Yesterday, 07:26 PM
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https://mars.nasa.gov/mer/home/

New status report and press release about the dust storm posted at the MER home page.
Misfortune for Opportunity but an opportunity for MAVEN.
QUOTE
Ever since the MAVEN orbiter entered Mars' orbit, "one of the things we've been waiting for is a global dust storm," said Bruce Jakosky, the MAVEN orbiter's princip[al] investigator.


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