Viking investigations of auroral electrodynamical processes
Viking investigations of auroral electrodynamical processes
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维京人对极光电动力学过程的研究
DOI：
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发表时间：
1993
期刊：
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通讯作者：
G. Marklund
中科院分区：
文献类型：
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作者：
G. Marklund
简要回顾了海盗号电场实验的最新结果及其对更好地理解极光和相关电离层-磁层过程的贡献。高分辨率电场数据在许多不同领域提供了新的重要结果，包括弧尺度和全球尺度的极光电动力学、极光加速过程、电流-电压关系、亚暴和极尖动力学。在简要介绍了高空电场资料的一些特征后，本文的其余部分重点讨论了电场在极光电动力学和极光加速过程中的作用。在维京事件研究和数值模型研究的基础上，讨论了极光发射与相关的电场、电流、粒子和电导率分布之间的关系。特别关注电离层对流和与北行星际磁场（IMF）极光分布相关的场向电流特征，例如theta极光或那些以经典极光椭圆的极向扩展的极光活动为特征的极光。数值模型结果说明了当前系统从典型的向南的国际货币基金组织形态转变为可能代表北向国际货币基金组织形态的过程中对流模式的演变，并结合维京号的观测结果进行了讨论。“直流”电场在极光加速过程中的作用得到了进一步的研究和澄清。通过对直接测量的平行电场及其与其他相关参数的关系的统计研究，数据表明可能存在向上和向下的平行电场。强烈的低频电场波动（< 1hz）已被证明在极光加速过程中起重要作用。在这个频率范围内，电场对电子来说是静态的，但对离子来说不是，从而产生选择性加速。这些波动很可能是密切相关的电离层离子逸出的热能的一部分。基于许多不同方法的加速势估计通常显示出良好的一致性，为“直流”电场在极光加速过程中的作用提供了令人信服的证据。
Recent results from the Viking electric field experiment and their contribution to a better understanding of the aurora and of associated ionosphere-magnetosphere processes are briefly reviewed. The high-resolution electric field data have provided new and important results in a number of different areas, including auroral electrodynamics both on the arc scale size and on the global scale, the auroral acceleration process, the current-voltage relationship, substorms, and the dynamics of the polar cusp. After a short introduction presenting some of the characteristic features of the high-altitude electric field data the remainder of this paper focuses on the role of the electric field in auroral electrodynamics and in the auroral acceleration process. The relationships between the auroral emissions and the associated electric field, current, particle, and conductivity distributions are discussed for both small-scale and large-scale auroral distributions on the basis of results from Viking event studies and from numerical model studies. Particular attention is paid to ionospheric convection and field-aligned current signatures associated with northward interplanetary magnetic field (IMF) auroral distributions, such as the theta aurora or those characterized by extended auroral activity poleward of the classical auroral oval. The evolution of the convection pattern as the current system changes from a typical configuration for southward IMF to a configuration that may be representative of northward IMF conditions is illustrated by numerical model results and discussed in the light of Viking observations. The role of “dc” electric fields for the auroral acceleration process has been further investigated and clarified. From a statistical study of the directly measured parallel electric field and its relation to other relevant parameters the data suggest the possible existence of both upward and downward parallel fields. Intense low-frequency electric field fluctuations (<1 Hz) have been shown to play an important role in the auroral acceleration process. In this frequency range the electric field appears static for the electrons but not for the ions, giving rise to a selective acceleration. The fluctuations are likely to contribute to the thermal energy of the closely associated escaping ionospheric ions. Estimates of the acceleration potential based on a number of different methods generally show good agreement, providing convincing evidence of the role of “dc” electric fields in the auroral acceleration process.