A comprehensive numerical simulation of Io’s sublimation-driven atmosphere
A comprehensive numerical simulation of Io’s sublimation-driven atmosphere
复制标题
对木卫一升华驱动大气的全面数值模拟
DOI：
10.1016/j.icarus.2010.01.012
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发表时间：
2010
期刊：
影响因子：
3.2
通讯作者：
B. Stewart
中科院分区：
文献类型：
--
作者：
A. Walker;Sergey L. Gratiy;D. Goldstein;C. Moore;P. Varghese;L. Trafton;D. Levin;B. Stewart
木卫一的升华驱动的大气层建模使用直接模拟蒙特卡罗（DSMC）方法。这些稀薄气体动力学模拟通过使用包含并行计算的整个行星的三维域来改进早期模型。等离子体加热，行星旋转，不均匀的表面霜，暴露的（非挥发性）岩石表面上的SO2分子停留时间，和表面温度分布的影响进行了研究。据预测，环行星流动将从温暖的昼侧向较冷的夜侧发展。木卫一的自转导致了霜层表面温度分布的高度不对称（由于霜层的高热惯性），这导致了围绕日下点不对称的环行星流动。大气的非平衡热结构，特别是振动和旋转温度，也进行了研究。等离子体加热被发现显着膨胀的大气在白天和黑夜。等离子体能量通量在高海拔处引起高温，但通过最热的霜上方的致密气柱的等离子体能量消耗允许气体温度低于低海拔处的表面。一张霜冻地图（Douté，S.，施密特，B.，洛佩斯-戈蒂埃河，卡尔森河，Soderblom，L.雪莉，J.，伽利略NIMS团队[2001]。Icarus 149，107-132）用于控制SO2的升华通量，这可能导致不均匀的柱密度，对于相同的表面温度，其变化几乎为四倍。SO2分子在“岩石”组分上的短停留时间被发现平滑由表面霜分布的变化引起的横向大气不均匀性，创造了一种看起来几乎与均匀霜覆盖相同的大气。发现较长的停留时间与中红外观测更一致（Spencer，J.R.，Lellouch，E.，Richter，M.J.，López-Valverde，文学硕士，杰瑟普，K.L，格雷特豪斯，T. K.，Flaud，J. [2005年]。Icarus 176，283-304），并重现了观测到的反木星/亚木星柱密度不对称。假设表面霜温为115 K，计算出的木卫一向阳面柱密度峰值与莱曼-α观测结果（Feaga，L.M.，麦格拉思，M.，费尔德曼警局[2009年]。伊卡洛斯201，570-584）。另一方面，在120 K时的峰昼侧柱密度是观测值的5倍，高于观测值的上限（杰瑟普，K.L.，斯宾塞J.R.巴列斯特，通用电气公司，R. R.豪厄尔，Roesler，F.，Vigel，M.，耶勒河[2004年]第10号一般性意见。Icarus 169，197-215; Spencer等人，2005年）。
Io’s sublimation-driven atmosphere is modeled using the direct simulation Monte Carlo (DSMC) method. These rarefied gas dynamics simulations improve upon earlier models by using a three-dimensional domain encompassing the entire planet computed in parallel. The effects of plasma heating, planetary rotation, inhomogeneous surface frost, molecular residence time of SO2on the exposed (non-volatile) rocky surface, and surface temperature distribution are investigated. Circumplanetary flow is predicted to develop from the warm dayside toward the cooler nightside. Io’s rotation leads to a highly asymmetric frost surface temperature distribution (due to the frost’s high thermal inertia) which results in circumplanetary flow that is not axi-symmetric about the subsolar point. The non-equilibrium thermal structure of the atmosphere, specifically vibrational and rotational temperatures, is also examined. Plasma heating is found to significantly inflate the atmosphere on both the dayside and nightside. The plasma energy flux causes high temperatures at high altitudes but plasma energy depletion through the dense gas column above the warmest frost permits gas temperatures cooler than the surface at low altitudes. A frost map (Douté, S., Schmitt, B., Lopes-Gautier, R., Carlson, R., Soderblom, L., Shirley, J., and the Galileo NIMS Team [2001]. Icarus 149, 107–132) is used to control the sublimated flux of SO2which can result in inhomogeneous column densities that vary by nearly a factor of four for the same surface temperature. A short residence time for SO2molecules on the “rock” component is found to smooth lateral atmospheric inhomogeneities caused by variations in the surface frost distribution, creating an atmosphere that looks nearly identical to one with uniform frost coverage. A longer residence time is found to agree better with mid-infrared observations (Spencer, J.R., Lellouch, E., Richter, M.J., López-Valverde, M.A., Jessup, K.L, Greathouse, T.K., Flaud, J. [2005]. Icarus 176, 283–304) and reproduce the observed anti-jovian/sub-jovian column density asymmetry. The computed peak dayside column density for Io assuming a surface frost temperature of 115K agrees with those suggested by Lyman-α observations (Feaga, L.M., McGrath, M., Feldman, P.D. [2009]. Icarus 201, 570–584). On the other hand, the peak dayside column density at 120K is a factor of five larger and is higher than the upper range of observations (Jessup, K.L., Spencer, J.R., Ballester, G.E., Howell, R.R., Roesler, F., Vigel, M., Yelle, R. [2004]. Icarus 169, 197–215; Spencer et al., 2005).