[X] My Assistant

[rlorenz]

Evidence of the diurnal pressure cycle in the radiation detector data, and the suggestion of dust devil encounters in the meteorology package (REMS) data.

http://www.jpl.nasa.gov/news/news.php?rele...elease_2012-361

Suggests 'over 20' events with one or more in-situ signatures of dust devil encounters (e.g. pressure drop, wind direction change etc.)
In 12 weeks that means only ~0.25 events per day, which is pretty low compared with Phoenix and Pathfinder
(more like 1-3 / day, depending on event threshold e.g. see http://www.lpl.arizona.edu/~rlorenz/dustde...ssuredrops.pdf) but we'll need to wait and see this published properly to understand what thresholds were used and what correction factors for observation duty cycle need to be applied.

[Eyesonmars]

Andy, the detector has a 65 degree cone of view normal to the rover body ( upward hopefully( i'm kidding))

Here is a quote from the Nov 15 press conference that is the core of my confusion.

"We see a definite pattern related to the daily thermal tides of the atmosphere," said RAD Principal Investigator Don Hassler of the Southwest Research Institute's Boulder, Colo., branch. "The atmosphere provides a level of shielding, and so charged-particle radiation is less when the atmosphere is thicker. Overall, Mars' atmosphere reduces the radiation dose compared to what we saw during the flight to Mars."

Hence my original question. What is it about the atmosphere that provides the shielding ? The gas or the dust? It should be easy to answer once we get RAD data over a wider range of tau and pressure values

[mcaplinger]

What is it about the atmosphere that provides the shielding ? The gas or the dust?

I think you'll find that the mass of the dust is negligible from a shielding perspective. From http://citeseerx.ist.psu.edu/viewdoc/downl...p1&type=pdf if you precipitated all the dust in the middle of a severe dust storm it would only form a layer 18 microns thick.