Magnetosphere-Atmosphere Coupling at Saturn: 1. Response of Thermosphere and Ionosphere to Steady State Polar Forcing
Magnetosphere-Atmosphere Coupling at Saturn: 1. Response of Thermosphere and Ionosphere to Steady State Polar Forcing
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DOI：
10.1016/j.icarus.2012.08.034
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发表时间：
2012-11
期刊：
影响因子：
3.2
通讯作者：
I. Müller-Wodarg;L. Moore;M. Galand;S. Miller;M. Mendillo
中科院分区：
文献类型：
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作者：
I. Müller-Wodarg;L. Moore;M. Galand;S. Miller;M. Mendillo
本文综合计算了土星热层-电离层耦合对太阳辐射、磁层高能电子沉淀和磁层等离子体亚自转引起的高纬度电场的稳态响应。我们的土星热层电离层环流模型（STIM-GCM）对计算的物理过程进行了重要补充，包括对中性离子动力学耦合的全面和自一致处理，以及使用自一致计算的入射高能电子产生等离子体的速率。我们的模拟成功地再现了观测到的高纬度温度以及由卡西尼无线电科学子系统实验（RSS）观测到的电离层峰值电子密度的纬度变化。我们发现磁层能量沉积强烈地控制着高纬度和中纬度热层的质量和能量流动，热层动力学在驱动这种流动中起着至关重要的作用，突出了在土星和其他气体巨星的任何高纬度能量平衡研究中包括动力学的重要性。通过将观测到的H3+柱发射和温度与从模拟大气剖面推断出的相同数量相关联，我们确定了一种潜在的方法，可以更好地约束振动激发的h2的未知丰度，它强烈影响H3+密度。我们的计算还表明，H3+柱发射通量的局部时间变化可能主要是由H3+密度的局部时间变化而不是温度变化驱动的。通过探索可能的高纬度电场强度和入射高能电子通量的参数空间，我们确定了热层极地温度对一系列磁层强迫参数的响应，表明0.1 - 1.2 mvm−2的10keV电子通量与80-100mVm−1的电场强度相结合产生的H3+发射与观测结果一致。我们的计算强调了考虑热层温度的重要性，当检查土星磁层的状态及其与上层大气的耦合时，热层温度是一个限制因素。
We present comprehensive calculations of the steady state response of Saturn’s coupled thermosphere–ionosphere to forcing by solar radiation, magnetospheric energetic electron precipitation and high latitude electric fields caused by sub-corotation of magnetospheric plasma. Significant additions to the physical processes calculated in our Saturn Thermosphere Ionosphere General Circulation Model (STIM–GCM) include the comprehensive and self-consistent treatment of neutral–ion dynamical coupling and the use of self-consistently calculated rates of plasma production from incident energetic electrons. Our simulations successfully reproduce the observed high latitude temperatures as well as the latitudinal variations of ionospheric peak electron densities that have been observed by the Cassini Radio Science Subsystem experiment (RSS). We find magnetospheric energy deposition to strongly control the flow of mass and energy in the high and mid-latitude thermosphere and thermospheric dynamics to play a crucial role in driving this flow, highlighting the importance of including dynamics in any high latitude energy balance studies on Saturn and other Gas Giants. By relating observed H3+column emissions and temperatures to the same quantities inferred from simulated atmosphere profiles we identify a potential method of better constraining the still unknown abundance of vibrationally excited H2which strongly affects the H3+densities. Our calculations also suggest that local time variability in H3+column emission flux may be largely driven by local time changes of H3+densities rather than temperatures. By exploring the parameter space of possible high latitude electric field strengths and incident energetic electron fluxes, we determine the response of thermospheric polar temperatures to a range of these magnetospheric forcing parameters, illustrating that 10keV electron fluxes of 0.1–1.2mWm−2in combination with electric field strengths of 80–100mVm−1produce H3+emissions consistent with observations. Our calculations highlight the importance of considering thermospheric temperatures as one of the constraints when examining the state of Saturn’s magnetosphere and its coupling to the upper atmosphere.