Are Io ’ s Alfvén wings filamented ? Galileo observations
Are Io ’ s Alfvén wings filamented ? Galileo observations
复制标题
木卫一的阿尔文翼是伽利略观测的丝状吗？
DOI：
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发表时间：
2005
期刊：
影响因子：
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通讯作者：
K. Khuranac
中科院分区：
文献类型：
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作者：
T. Chusta;A. Rouxa;W. S. Kurthb;D. A. Gurnettb;M. G. Kivelsonc;K. Khuranac
木卫一与木星磁层的相互作用产生极光和射电辐射。潜在的电子加速过程尚不清楚，并且存在很少的观测来约束理论模型。电子加速的能量来源很可能是由从木卫一两极延伸到木星两个半球的阿尔夫萨芬双翼提供的。与阿尔夫萨芬双翼有关的当前系统的形式一直存在争议，一些人认为木卫一附近的水流大大减缓，意味着木卫一与木星电离层之间存在一个稳定的电流环，另一些人认为返回波只出现在木卫一的下游，还有一些人认为两种形式都有发展。考虑到alfv<s:1>马赫数的有限值所暗示的alfv<s:1>机翼的有限倾角，以及发生在木卫一环边界的强反射，我们认为木卫一和木星电离层之间不可能产生稳定的电流环。然而，极光和无线电发射的能量学表明，在高纬度地区，即在木卫一环外，阿尔夫萨芬机翼中的大部分能量转化为电子加速度。那么，难题就在于如何理解大部分能量是如何穿透反射边界的。我们提供了伽利略多次飞越木卫一的数据，表明与木星电离层的耦合是由与从环面传播的电磁波相关的纤丝alfv<s:1>机翼介导的。特别是，我们报告了系统观测，在艾奥的alfvsamn翼的横截面内及其附近，频率高达几倍于质子回旋频率的强烈电磁波。我们将这些“高频/小尺度”波解释为阿尔夫萨芬星云翼在反射出木卫一环的尖锐边界梯度之前的强烈丝化/碎裂的特征。因此，我们认为，大部分初级能量被转换成“高频/小尺度”电磁波，可以从木星的环面传播到木星的电离层。在高纬度地区，这些波能够将电子加速到几乎相对论的速度。2004爱思唯尔有限公司版权所有。
The interaction of Io with the Jovian magnetosphere generates auroral and radio emissions. The underlying electron acceleration process is not understood and few observations exist to constrain the theoretical models. The source of energy for the electron acceleration is in all likelihood supplied from the Alfvén wings that stretch out from both poles of Io into the two Jovian hemispheres. The form of the current system associated with the Alfvén wings has been disputed, some suggesting that the greatly slowed flow near Io implies that a steady current loop links Io to Jupiter’s ionosphere, others arguing that the return waves appear only downstream of Io and others suggesting that both forms develop. Given the finite inclination of the Alfvén wings implied by the finite value of the Alfvén Mach number and the strong reflection that occurs at the boundary of the Io torus, we argue that no steady current loop can be invoked between Io and Jupiter’s ionosphere. However, the energetics of the auroral and radio emissions imply that most of the energy in the Alfvén wings is transformed into electron acceleration at high-latitudes, that is, outside the Io torus. The dilemma then is to understand how a large fraction of the power penetrates the reflecting boundary. We present data from Galileo’s multiple flybys of Io that suggest that the coupling with the Jovian ionosphere is mediated by filamentary Alfvén wings associated with electromagnetic waves propagating out of the torus. In particular, we report on the systematic observation, within the cross-section of Io’s Alfvén wings and in their immediate vicinity, of intense electromagnetic waves at frequencies up to several times the proton gyrofrequency. We interpret these ‘‘high-frequency/small-scale’’ waves as the signature of a strong filamentation/ fragmentation of the Alfvén wings before they reflect off of the sharp boundary gradient of the Io torus. As a consequence, we suggest that most of the primary energy is converted into ‘‘high-frequency/small-scale’’ electromagnetic waves that can propagate out from the torus toward Jupiter’s ionosphere. Reaching high-latitudes, these waves are able to accelerate electrons to almost relativistic speeds. r 2004 Elsevier Ltd. All rights reserved.