Dawn-Dusk Asymmetry and Spongy Nature of the Jovian Magnetosphere
Dawn-Dusk Asymmetry and Spongy Nature of the Jovian Magnetosphere
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木星磁层的黎明-黄昏不对称性和海绵性质
DOI：
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发表时间：
1985
期刊：
影响因子：
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通讯作者：
H. Oya
中科院分区：
文献类型：
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作者：
T. Aoyama;H. Oya
基于超磁声速木星盘风的局域流动区存在的盘状等离子体，研究了木星磁层在赤道平面内的动力学特征。利用磁层顶内外压强相互平衡的概念，得到了描述木星磁层形状的压强平衡方程，并进行了数值计算。支撑太阳风压的主要气压不是行星磁压，而是木星盘风的动压。因此，木星盘风的性质对木星磁层的形状有很大的影响。压力平衡方程的数值计算结果表明木星磁层具有明显的黎明-黄昏不对称性，即木星在黎明时有一个大尺度的磁层，而在黄昏时有一个相对较小的磁层。我们的计算还表明，木星磁层顶的位置对太阳风压的变化有一个敏感的响应。这一特征与先驱者10号、11号、旅行者1号和旅行者2号的现场观测结果不谋而合，被称为木星磁层的“海绵性”。除了计算超磁声风的解外，我们还得到了亚磁声风情况下的磁层形状。微风情况下的结果表明，稳定的磁层顶只能在白天的有限区域内存在。
Being based on the existence of the disc plasma flowing outward in the localized flow region with the super magnetosonic velocity called Jovian disc wind, a dynamical feature of the Jovian magnetosphere has been studied in the equatorial plane. Using a concept that the pressures inside and outside of the magnetopause are balanced by each other, a pressure balance equation has been obtained and calculated numerically to express the shape of the Jovian magnetosphere. The main pressure supporting the solar wind pressure is not the planetary magnetic pressure but the dynamic pressure of the Jovian disc wind. The nature of the Jovian disc wind with large azimuthal component in its bulk flow, therefore, has a great influence on the shape of the Jovian magnetosphere. The results of our numerical calculation of the pressure balance equation indicate a clear dawn-dusk asymmetry of the Jovian magnetosphere; i. e., Jupiter has a large scale magnetosphere in the dawn side and has a relatively small scale magnetosphere in the dusk side. Our calculation also indicates a sensitive response of the location of the Jovian magnetopause for the variation of the solar wind pressure. This feature coincides with the in-situ observations by Pioneer 10, 11, Voyager 1 and 2, and is called the “spongy nature” of the Jovian magnetosphere. In addition to the calculation for the super magnetosonic wind solution, we have obtained the shape of the magnetosphere for the case of sub-magnetosonic breeze. The results for the breeze case indicate that the stable magnetopause is able to exist only in the limited region in the day side.