Wednesday, February 11, 2009

LPSC 2009: Simulated Plumes with Irregular Vents

Next up in our series on Io-abstracts at this year's LPSC is "DSMC Modeling of 3D Vent Geometries for Ionian Plumes" by William McDoniel, D. Goldstein, P. Varghese, L. Trafton, and B. Stewart. This abstract covers part of continuing research to study Io's atmospheric and volcanic plume dynamics using Direct Simulation Monte Carlo (DSMC) modeling. In this abstract, McDoniel et al. take a look at volcanic plumes with irregularly shaped plume vents.

The University of Texas research team led by Dr. David Goldstein have been modeling the plumes and atmosphere of Io for a number of years using a model called the Direct Simulation Monte Carlo method. From the Wikipedia article, "DSMC is a numerical method for modeling rarefied gas flows, in which the mean free path of a molecule is of the same order (or greater) than a representative physical length scale (i.e. the Knudsen number Kn is greater than 1)." I quoted that because, while I understand the individual words in that sentence, I'm not sure I would have summarized that properly. So while I may not have a perfect understanding of the method the group uses, I can't argue with results as they have managed, in prior work, to create a proper looking Pele-type plume in Zhang et al. 2003 and dust plume in Zhang et al. 2004. More recently, they have used the DSMC method to look at Io's atmospheric collapse when the satellite enters Jupiter's shadow.

In the research group's previous work with plumes, they assumed a disk-shaped source vent for the plume. First, assume a spherical cow... :-D Well, in McDoniel et al., Goldstein's group decided to look at the effect of a non-circular source vent. This would better match the source vents observed on Io. Prometheus's plume is thought to be generated as an advancing lava flow front cover over pre-existing sulfur dioxide surface frost, causing the ice to become heated and sent skyward to become part of the plume. Tvashtar's plume is thought to be formed at a somewhat linear lava curtain. In short, neither plume, nor other plumes on Io, seems to have a "disk-shaped" source vent. So the authors performed their DSMC simulation, with a Io temperature and atmospheric conditions, using a half-annular vent and compared the resulting plume with a previous simulation using similar conditions but with a disk-shaped source.

The authors found that even with an asymmetric source vent, the resulting plume shape is very similar to the axisymmetric case. All the differences in particle density that are apparent near the vent become smeared out before the particles even reach the top of the plume, or the shock canopy. The plume fallout zone is roughly axisymmetric around the half-annular source vent. This model is supported by observation. At Prometheus, there appears to be an irregular-shaped source region (rather than a specific vent crater) but the plume fallout pattern is circular around that source. A similar case can be seen at Pele. What is apparent from the simulation is that high-resolution images of a plume would be required to observe differences in the plume's shape (particularly the particle density near the vent) as a result of the vent shape.

It is nice to see that the DSMC model bear out what has been observed at Galileo once again. However, if anyone on the UT research group is reading this, please, please, perform a simulation with two plumes near each other. We have now observed a number of cases of interaction between two volcanic plumes at Io (Pele/Pillan in 1997, the two Masubi plumes in 2007, the two Kanehekili plumes in 1997, and the two Loki plumes in 1979). We have also seen similar interactions between a dominant dust plume and a much smaller sulfur-rich plume based on surface fallout patterns (like at Marduk and Prometheus). It would be interesting to see what these would look like modeled.

Link: DSMC Modeling of 3D Vent Geometries for Ionian Plumes []

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