The Effect of Plasma Heating on Sublimation-Driven Flow in Io's Atmosphere
The Effect of Plasma Heating on Sublimation-Driven Flow in Io's Atmosphere
复制标题
等离子体加热对木卫一大气中升华驱动流的影响
DOI：
10.1006/icar.1995.1082
复制
发表时间：
1995
期刊：
影响因子：
3.2
通讯作者：
Robert E. Johnson
中科院分区：
文献类型：
--
作者：
M. Wong;Robert E. Johnson
摘要：木卫一上的大气流动是在平面二维轴对称几何结构中对后半球上的升华大气进行数值计算的，该大气受到等离子体轰击、紫外线加热和红外线冷却。计算的太阳下蒸气压为～6.5 × 10 3 Pa (～3 × 10 18 SO 2 /cm 2 )和6.8 × 10 -4 Pa (～4 × 10 17 SO 2 /cm 2 )；后者近似于 F. P. Fanale 等人的蒸气压。 （1982 年，《木星卫星》，第 756-781 页，亚利桑那大学出版社，图森）。由于共旋转，沉积在大气中的等离子体能量是等离子体流能量的20％(J.A.Linker等，1988，Geophys，Res.Lett.15，1311-3141)。研究发现，等离子体加热使上层大气显着膨胀，增加了外层高度和被外层气体柱覆盖的表面量。这反过来控制了 Io 等离子体环的供应（M. A. McGrath 和 R. E. Johnson, 1987, Icarus 69, 519-531）。质量和能量的水平流动对于确定外底高度也很重要；结果表明，尽管我们使用纯 SO 2 气体的平衡冷却至空间近似（E. Lellouch 等人，1992，Icarus 98, 271-295）可能会高估这种效应，但红外冷却可能很重要。计算出的外基高度略低于 McGrath 和 Johnson (1987) 提出的提供环面的高度，表明外基附近等离子体能量沉积和溅射喷射速率的细节以及该区域的红外发射需要检查。此外，与分子光解离时间相比，从表面升华（或溅射）的分子被传输到外切碱基的时间短。因此，外切碱基由分子种类主导，并且外切碱基由表面的小区域提供。
Abstract The atmospheric flow on Io is numerically computed in a flat 2-D axisymmetric geometry for a sublimation atmosphere on the trailing hemisphere subjected to plasma bombardment, UV heating, and IR cooling. Calculations are performed for subsolar vapor pressures of ∼6.5 × 10 3 Pa (∼3 × 10 18 SO 2 /cm 2 )and 6.8 × 10 -4 Pa (∼4 × 10 17 SO 2 /cm 2 ); the latter approximates the vapor pressure of F. P. Fanale et al. (1982, Satellites of Jupiter , pp. 756-781, Univ. of Arizona Press, Tucson). The amount of plasma energy deposited in the atmosphere is 20% of the plasma flow energy due to corotation (J. A. Linker et al. , 1988, Geophys, Res. Lett. 15, 1311-3141). It is found that plasma heating significantly inflates the upper atmosphere, increasing both the exobase altitude and the amount of surface covered by more than an exospheric column of gas. This in turn controls the supply of the Io plasma torus (M. A. McGrath and R. E. Johnson, 1987, Icarus 69, 519-531). The horizontal flow of mass and energy is also important in determining the exobase altitude; and it is shown that IR cooling can be important, although our use of the equilibrium, cool-to-space approximation for a pure SO 2 gas (E. Lellouch et al. , 1992, Icarus 98, 271-295) may overestimate this effect. The calculated exobase altitudes are somewhat lower than those suggested by McGrath and Johnson (1987) for supplying the torus, indicating the details of the plasma energy deposition and sputter ejection rate near the exobase, as well as the IR emission from this region need to be examined. In addition, the molecules sublimed (or sputtered) from the surface are transported to the exobase in times short compared to the molecular photodissociation time. Therefore, the exobase is dominated by molecular species and the exobase is supplied by a small region of the surface.