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Supersonic Meteorology of Io: Sublimation-Driven Flow of SO_2

Ingersoll, Andrew P. and Summers, Michael E. and Schlipf, Steve G. (1985) Supersonic Meteorology of Io: Sublimation-Driven Flow of SO_2. Icarus, 64 (3). pp. 375-390. ISSN 0019-1035. doi:10.1016/0019-1035(85)90062-4.

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The horizontal flow of SO_2 gas from day side to night side of Io is calculated. The surface is assumed to be covered by a frost whose vapor pressure at the subsolar point is orders of magnitude larger than that on the night side. Temperature of the frost is controlled by radiation. The flow is hydrostatic and turbulent, with velocity and entropy per particle independent of height. The vertically integrated conservation equations for mass, momentum, and energy are solved for atmospheric pressure, temperature, and horizontal velocity as functions of solar zenith angle. Formulas from boundary layer theory govern the interaction between atmosphere and surface. The flow becomes supersonic as it expands away from the subsolar point, as in the theory of rocket nozzles and the solar wind. Within 35° of the subsolar point atmospheric pressure is less than the frost vapor pressure, and the frost sublimes. Elsewhere, atmospheric pressure is greater than the frost vapor pressure, and the frost condenses. The two pressures seldom differ by more than a factor of 2. The sublimation rate at the subsolar point is proportional to the frost vapor pressure, which is a sensitive function of temperature. For a subsolar temperature of 130°K, the sublimation rate is 10^(15) molecules/cm^2/sec. Diurnally averaged sublimation rates at the equator are comparable to the 0.1 cm/year resurfacing rate required for burial of impact craters. At the poles where both the vapor pressures and atmospheric pressures are low, the condensation rates are 100 times smaller. Surface pressures near the terminator are generally too low to account for the ionosphere discovered by Pioneer 10. The possibility of a noncondensable gas in addition to SO_2 must be seriously considered.

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Ingersoll, Andrew P.0000-0002-2035-9198
Additional Information:© 1985 Academic Press, Inc. Received August 19, 1985; revised November 4, 1985. This research was supported by the Planetary Atmospheres Program and the Planetary Astronomy Program of NASA.
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Issue or Number:3
Record Number:CaltechAUTHORS:20121205-141815339
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Official Citation:Andrew P. Ingersoll, Michael E. Summers, Steve G. Schlipf, Supersonic meteorology of Io: Sublimation-driven flow of SO2, Icarus, Volume 64, Issue 3, December 1985, Pages 375-390, ISSN 0019-1035, 10.1016/0019-1035(85)90062-4. (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:35835
Deposited By: Ruth Sustaita
Deposited On:05 Dec 2012 22:36
Last Modified:09 Nov 2021 23:18

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