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首页> 外文期刊>Space Science Reviews >Electric Fields and Plasma Processes in the Auroral Downward Current Region, Below, Within, and Above the Acceleration Region
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Electric Fields and Plasma Processes in the Auroral Downward Current Region, Below, Within, and Above the Acceleration Region

机译：加速区域以下，内部和上方的极光向下电流区域中的电场和等离子体过程

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The downward field-aligned current region plays an active role in magnetosphere-ionosphere coupling processes associated with aurora. A quasi-static electric field structure with a downward parallel electric field forms at altitudes between 800 km and 5000 km, accelerating ionospheric electrons upward, away from the auroral ionosphere. A wealth of related phenomena, including energetic ion conics, electron solitary waves, low-frequency wave activity, and plasma density cavities occur in this region, which also acts as a source region for VLF saucers. Results are presented from sounding rockets and satellites, such as Freja, FAST, Viking, and Cluster, to illustrate the characteristics of the electric fields and related parameters, at altitudes below, within, and above the acceleration region. Special emphasis will be on the high-altitude characteristics and dynamics of quasi-static electric field structures observed by Cluster. These structures, which extend up to altitudes of at least 4–5 Earth radii, appear commonly as monopolar or bipolar electric fields. The former are found to occur at sharp boundaries, such as the polar cap boundary whereas the bipolar fields occur at soft plasma boundaries within the plasma sheet. The temporal evolution of quasi-static electric field structures, as captured by the pearls-on-a-string configuration of the Cluster spacecraft indicates that the formation of the electric field structures and of ionospheric plasma density cavities are closely coupled processes. A related feature of the downward current often seen is a broadening of the current sheet with time, possibly related to the depletion process. Preliminary studies of the coupling of electric fields in the downward current region, show that small-scale structures appear to be decoupled from the ionosphere, similar to what has been found for the upward current region. However, exceptions are also found where small-scale electric fields couple perfectly between the ionosphere and Cluster altitudes. Recent FAST results indicate that the degree of coupling differs between sheet-like and curved structures, and that it is typically partial. The mapping depends on the current-voltage relationship in the downward current region, which is highly non-linear and still unclear, as to its specific form. Keywords Auroral electric field - Auroral particle acceleration - Auroral processes - Satellite observations - Cluster observations - Auroral downward current - Electric field coupling
机译：向下的磁场对准的电流区域在与极光相关的磁层-电离层耦合过程中起着积极作用。在800 km和5000 km之间的高度形成具有向下平行电场的准静态电场结构，使电离层电子向上加速，远离极光电离层。此区域中发生了许多相关现象，包括高能离子圆锥，电子孤波，低频波活动和等离子体密度腔，这也是VLF碟的源区域。结果来自探测火箭和卫星（例如Freja，FAST，Viking和Cluster），以说明加速区域以下，内部和上方的高度处的电场特性和相关参数。特别强调的是星团观测到的准静态电场结构的高空特征和动力学。这些结构延伸到至少4-5地球半径的高度，通常以单极或双极电场的形式出现。发现前者出现在尖锐的边界处，例如极性帽边界，而双极场发生在等离子片内的软等离子边界处。由簇状航天器的串珠状构造捕获的准静态电场结构的时间演变表明，电场结构的形成和电离层等离子体密度腔是紧密耦合的过程。经常看到的向下电流的一个相关特征是电流表随时间的扩大，可能与耗尽过程有关。对向下电流区域中电场耦合的初步研究表明，小规模结构似乎已与电离层解耦，类似于在向上电流区域中发现的结构。但是，在电离层和星团高度之间完美耦合了小规模电场的情况也被发现。最近的FAST结果表明，片状和弯曲结构之间的耦合程度不同，并且通常是局部的。映射取决于向下电流区域中的电流-电压关系，就其特定形式而言，该关系是高度非线性的并且仍然不清楚。关键词极光电场-极光粒子加速度-极光过程-卫星观测-团簇观测-极光向下电流-电场耦合

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