Computer Science – Sound
Scientific paper
Sep 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008dps....40.4407m&link_type=abstract
American Astronomical Society, DPS meeting #40, #44.07; Bulletin of the American Astronomical Society, Vol. 40, p.478
Computer Science
Sound
Scientific paper
One dimensional direct simulation Monte Carlo (DSMC) calculations are used to examine the effects of a non-condensable species on the freeze-out dynamics of Io's SO2 sublimation atmosphere during and just after eclipse. Virtually no change to atmospheric properties occurs at altitudes above 100 km during the first 10 minutes of eclipse because of the finite ballistic time and sound speed. Therefore, immediately after ingress the auroral emission morphology above 100 km should resemble that of the immediate pre-eclipse state. In the absence of a non-condensable species the SO2 sublimation atmosphere will freeze-out (collapse) during eclipse as the surface temperature drops. However, rapid collapse is prevented by the presence of even a small amount of non-condensable gas due to the formation of a static diffusion layer of the non-condensable several mean free paths thick near the surface. A higher non-condensable mole fraction correlates with a longer collapse time. Because gas species may not be non-condensable at Io's surface temperatures, the effect of a weakly condensable gas species (non-zero sticking/reaction coefficient) was examined. It is found that even a small sticking coefficient dramatically reduces the effect of the diffusion layer on the dynamics and if the sticking coefficient exceeds 0.25, the collapse dynamics are effectively the same as if there were no "non-condensable” present. The reason for the sensitivity is twofold. First, the loss of "non-condensable” to the surface reduces the diffusion layer size relative to the mean free path. Second, if the surface is a partial sink, then the "non-condensable” layer is no longer stationary and the SO2 convects to the surface. As the surface temperature increases during egress, the sublimating SO2 gas pushes the non-condensable diffusion layer up to higher altitudes once it becomes dense enough to be collisional. This vertical species stratification should alter the aurorae after egress.
Goldstein David B.
Moore Chris H.
Stewart David B.
Trafton Larry M.
Varghese Philip L.
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