Alfven wings and electromagnetic induction in the interiors: Europa and Callisto
Alfven wings and electromagnetic induction in the interiors: Europa and Callisto
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DOI：
10.1029/1999ja900217
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发表时间：
1999-12-01
影响因子：
2.8
通讯作者：
Neubauer, FM
中科院分区：
文献类型：
--
作者：
Neubauer, FM
最近的证据的重要性，由于电磁感应的磁场在卫星欧罗巴和木卫四的内部进行激励阿尔芬翼模型的扩展，包括感应效应。这是由于木星磁层场在卫星位置的时间变化。我们表明，在一个卫星的感应效应的最大强度在木星的会合旋转增加的函数，从木星的距离，因为越来越重要的电流片。对于修正的Alfven机翼，我们得到了下列结果，这些结果也是Galileo最近的结果的顺序：（1）对于很小的Alfven马赫数，诱导效应使最大Alfven机翼气流减小。这种行为是有利的进行卫星内部和外部电离层边界之间的小距离。(2)在木星的会合旋转过去的卫星阿尔芬翼是最强的中央电流片的交叉点，而感应磁场是最显着的最大磁纬度。这一结果可能对卫星足迹观测很重要。(3)如果电离层电导率分布在上游和下游之间是对称的，则第1项中的最大阿尔芬翼电流也适用于稍大的阿尔芬马赫数。对于下游的主导电导率的最大阿尔芬翼电流增强，反之亦然，相反的电导率分布。(4)卫星轨道器的磁场测量可用于探测其导电内部，例如任何含盐海洋。
The recent evidence for the importance of magnetic fields due to electromagnetic induction in the conducting interiors of the satellites Europa and Callisto has motivated this extension of the Alfven wing model to include induction effects. These are due to the temporal variations of the Jovian magnetospheric field at the satellite positions. We show that the maximum strength of the induction effects in a satellite during a Jovian synodic rotation increases as a function of distance from Jupiter because of the increasing significance of the current sheet. For the modified Alfven wings we obtain the following results which also order the recent Galileo results: (1) For very small Alfven Mach numbers the maximum Alfven wing currents are reduced by the induction effects. This behavior is favored by a small distance between the conducting satellite interior and outer ionospheric boundary. (2) During a Jovian synodic rotation past a satellite the Alfven wings are strongest at crossings of the central current sheet, whereas induction magnetic fields are most significant at maximum magnetic latitude. This result may be important for satellite footprint observations. (3) The maximum Alfven wing current in item 1 also applies for somewhat larger Alfven Mach numbers, if the ionospheric conductivity distribution is symmetric between the upstreamside and the downstreamside. For a dominating conductivity on the downstreamside the maximum Alfven wing current is enhanced and vice versa for the opposite conductivity distribution. (4) Magnetic field measurements from satellite orbiters can be used to probe their conducting interiors, for examples any salty oceans.