Ionospheric depletion in auroral downward currents
Ionospheric depletion in auroral downward currents
复制标题
极光下行流中的电离层损耗
DOI：
10.1029/2007ja012350
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发表时间：
2007
期刊：
影响因子：
--
通讯作者：
A. Hood
中科院分区：
文献类型：
--
作者：
Alexandra P. Cran;A. Wright;A. Hood
[1]极光向下的场对齐电流主要由源自电离层的电子沿着地球的高纬度场线加速进入磁层。电离层是一个有限的电子来源：因此，如果电流要继续流动，自然会认为电流区必须扩大以获得更多的电流载流子。本文提出了一个磁层-电离层相互作用的Alfven波模型来描述电离层E区数密度在下行电流影响下的演化。系统的行为根据量=j0/αen2h值是大于还是小于1(其中j0是初始电流密度，α是复合系数，Ne是背景E区数密度，h是E区高度)分为两个区域：如果电流密度小于临界电流密度，jc=αen2hh(即1)，那么为了获得足够的电子，电流区被强迫加宽。在白天，典型的E区数密度是∼1011 m−3，只有非常强的电流密度∼10μA m−2才会发生展宽；然而，在黑夜侧，E区数密度可以下降10倍，任何大于∼0.1μA m−2的电流密度都会发生展宽。从这个模型，我们推导出了最终耗尽宽度(通常是原始电流区宽度的∼1-10倍)和特征耗尽时间标度(通常是∼10-100 S)的表达式。
[1] The auroral downward field-aligned current is mainly carried by electrons of ionospheric origin accelerated into the magnetosphere along the Earth's high-latitude field lines. The ionosphere is a finite source of electrons: Thus, if a current is to continue to flow, it is natural to assume that the current region must broaden to access more current carriers. In this paper, we present an Alfven wave model of magnetosphere-ionosphere interaction to describe the evolution of ionospheric E region number density under the influence of a downward current. The behavior of the system falls into two regimes depending upon whether the quantity = j0/αene2h is greater or less than unity (where j0 is initial current density, α is the recombination coefficient, ne is background E region number density, and h is E region height): If the current density is smaller than a critical current density, jc = αene2h (i.e., 1), then the current region is forced to broaden in order to access sufficient electrons. On the dayside, where a typical E region number density is ∼1011 m−3, broadening only occurs for very strong current densities ∼10 μA m−2; on the nightside, however, where E region number densities can fall by a factor of 10, broadening occurs for any current density greater than ∼0.1 μA m−2. From this model, we derive expressions for the final depletion width (generally ∼1–10 times the width of the original current region) and for the characteristic timescale of depletion (typically ∼10–100 s).