Compression of Jupiter's magnetosphere by the solar wind
Compression of Jupiter's magnetosphere by the solar wind
复制标题
太阳风对木星磁层的压缩
DOI：
10.1029/ja083ia10p04733
复制
发表时间：
1978
影响因子：
--
通讯作者：
J. Wolfe
中科院分区：
文献类型：
--
作者：
E. Smith;R. W. Fillius;J. Wolfe
报告了先驱者10号和11号遭遇期间太阳风的主要变化及其对木星磁层大小的影响的研究。喷气推进实验室矢量氦磁力计、艾姆斯研究中心等离子体分析仪和加州大学圣地亚哥分校捕获辐射探测器同时获得的遭遇数据集已与姐妹航天器在行星际空间同时获得的数据进行了比较。特别令人感兴趣的是，在四个间隔期间，飞船似乎在首次进入磁层接近100 RJ后，又在接近50 RJ的地方重新进入磁鞘。这项研究的主要结果是，在其中三种情况下，当高速太阳风流及其相关的相互作用区域预计将到达木星时，重新进入磁鞘。因此，这项研究支持了先前提出的假设，即木星的磁层经历了大规模的压缩。这一结果与另一种假设相反，即先驱者号穿越了磁层内可能与等离子体流出有关的空间区域。第四个案例是由先锋11号观测到的，似乎发生在安静的行星际条件下。然而，在这段时间内对磁场和等离子体数据的详细重新调查表明，航天器重新进入了磁鞘，而不是磁层内部的区域。重新进入磁鞘和随后返回磁层的间隔为10小时，预计将在航天器处于最高磁纬度时发生。初步得出的结论是，这次再入是木星磁层固有的大规模南北运动的结果。磁层顶内部的磁场是否足够强大，足以承受入射太阳风的压力，这个问题在本研究的背景下得到了重新审视。磁场似乎能够抵挡100 RJ和接近50 RJ的太阳风。木星磁层的可压缩性增强是因为磁层顶内部的磁场不是行星磁场，而主要是由磁层内部的电流引起的，可能是赤道流片。研究了磁层压缩时高能俘获辐射的可能加速。粒子通量的增加与磁场的比较表明回旋加速器的加速度可以忽略不计。根据测量到的粒子增强与到达宇宙飞船磁层顶之间的时间差，导出了磁层内平均等离子体密度为1-10 cm−3的估计值。最后，适合于木星磁层电路模型的特征时间常数估计在15到50小时之间。
A study of the major changes in the solar wind during the Pioneer 10 and 11 encounters and their influence on the size of the Jovian magnetosphere is reported. Simultaneous sets of encounter data acquired by the Jet Propulsion Laboratory vector helium magnetometer, the Ames Research Center plasma analyzer, and the University of California at San Diego trapped radiation detector have been compared with data acquired simultaneously in interplanetary space by the sister spacecraft. Of particular interest were four intervals during which it appeared that the spacecraft had reentered the magnetosheath near 50 RJ after having first entered the magnetosphere near 100 RJ. The principal outcome of the study is that in three of these cases the reentries into the magnetosheath occurred when high-speed solar wind streams and their associated interaction regions were expected to arrive at Jupiter. Thus the study supports the hypothesis advanced previously that the Jovian magnetosphere had undergone a large-scale compression. The results are contrary to an alternative hypothesis that the Pioneers had traversed a spatial region located inside the magnetosphere possibly associated with plasma outflow. The fourth case, which was observed by Pioneer 11 outbound, appears to have occurred during quiet interplanetary conditions. However, a detailed reinvestigation of magnetic field and plasma data during this interval shows that the spacecraft had reentered the magnetosheath and not a region interior to the magnetosphere. The reentry into the magnetosheath and the subsequent return to the magnetosphere were separated by an interval of 10 hours and would have been expected to occur when the spacecraft was at its highest magnetic latitude. It is concluded, tentatively, that this reentry was the result of a large-scale north-south motion intrinsic to the Jovian magnetosphere. The question of whether or not the magnetic field just inside the magnetopause is sufficiently strong to withstand the pressure of the incident solar wind has been reexamined within the context of this present study. The field appears able to hold off the solar wind both at 100 RJ and near 50 RJ. The compressibility of the Jovian magnetosphere is enhanced because the field inside the magnetopause is not the planetary field but is principally caused by currents inside the magnetosphere, presumably the equatorial current sheet. The possible acceleration of energetic trapped radiation when the magnetosphere was compressed has been investigated. Comparison of the increased particle fluxes and the magnetic field shows that gyrobetatron acceleration can be discounted. Based on the measured time difference between the particle enhancement and the arrival of the magnetopause at the spacecraft, an estimate is derived for the average plasma density inside the magnetosphere of 1–10 cm−3. Finally, the characteristic time constants appropriate to an electric circuit model of Jupiter's magnetosphere have been estimated as being in the range between 15 and 50 hours.