Abstract Io’s plasma interaction creates an electromagnetic coupling between Io and Jupiter through Alfven waves triggering the generation of auroral footprints in Jupiter’s southern and northern hemispheres. The brightness of Io’s footprints undergoes periodic variations that are primarily modulated by Io’s local plasma interaction through the Poynting flux radiated away from the moon. The periodic pattern with two maxima near 110∘ and 290∘ Jovian longitude where Io crosses the dense plasma sheet is generally understood. However, some characteristics, like the 2–4 times stronger brightening of the southern footprint near Jovian longitude 110∘ or the lack of response to Io’s eclipse passage, are not fully understood. We systematically study variations in Io’s plasma interaction and the Poynting flux using a 3D magnetohydrodynamic model, performing a series of simulations with different upstream plasma conditions and models of Io’s atmosphere. Our results indicate that the strong Jovian magnetic field near 110∘ plays a more important role than previously estimated for the strong brightening there. We find that the Poynting flux is not fully saturated for a wide range of possible atmospheric densities ( 6 × 10 18 – 6 × 10 21 m−2) and that density changes in the atmosphere by a factor of > 3, as possibly happening during Io’s eclipse passage, lead to a change of the Poynting flux by > 20%. Assuming that these expected changes in Poynting flux also apply to the footprints, the non-detection of a dimming in the footprint during the eclipse by Juno-UVS suggests that Io’s global atmospheric density decreases by a factor of 2.5. We show that for smaller atmospheric scale heights (i.e. a more confined atmosphere), changes in the atmospheric density have less effect on the Poynting flux. The missing response of the footprint to the eclipse hence might also be consistent with a density decrease by a factor of > 3, if the effective atmospheric scale height is small ( 120 km). Finally, we provide new analytical approximations that can be used for analyzing the effect of the local interaction responsible for the footprint variability in future studies.

中文翻译：

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Io 坡印廷通量的可变性：使用 MHD 模拟的参数研究

摘要 艾欧的等离子体相互作用通过阿尔文波在艾欧和木星之间产生电磁耦合，从而触发木星南半球和北半球极光足迹的产生。艾欧脚印的亮度会经历周期性变化，这主要是由艾欧局部等离子体相互作用通过远离月球辐射的坡印廷通量调制的。木星经度 110∘ 和 290∘ 附近有两个最大值的周期性模式通常被理解，在那里 Io 穿过致密的等离子层。然而，一些特征，例如木星经度 110∘ 附近南部足迹的 2-4 倍增亮或对艾奥的日食通道缺乏反应，尚不完全清楚。我们使用 3D 磁流体动力学模型系统地研究了艾欧等离子体相互作用和坡印廷通量的变化，使用不同的上游等离子体条件和艾欧大气模型进行一系列模拟。我们的结果表明，110∘附近的强木星磁场对那里的强增亮起着比先前估计的更重要的作用。我们发现坡印廷通量在各种可能的大气密度 (6 × 10 18 – 6 × 10 21 m−2) 下都没有完全饱和，并且大气中的密度变化大于 3，这可能发生在艾欧的日食通道导致坡印廷通量的变化 > 20%。假设坡印廷通量的这些预期变化也适用于足迹，Juno-UVS 在日食期间未检测到足迹变暗表明艾奥的全球大气密度降低了 2.5 倍。我们表明，对于较小的大气尺度高度（即更封闭的大气），大气密度的变化对坡印廷通量的影响较小。因此，如果有效大气尺度高度较小（120 公里），则足迹对日食的缺失响应也可能与密度降低 3 倍以上一致。最后，我们提供了新的分析近似值，可用于分析导致未来研究中足迹可变性的局部相互作用的影响。