A source for field‐aligned currents at auroral latitudes
A source for field‐aligned currents at auroral latitudes
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DOI：
10.1029/ja074i001p00247
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发表时间：
1969
影响因子：
--
通讯作者：
M. Schield;J. Freeman;A. Dessler
中科院分区：
文献类型：
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作者：
M. Schield;J. Freeman;A. Dessler
高能等离子体从地球磁层尾部的等离子体片向地球漂移，其终端是一个内边界（阿尔芬层）。场向电流（Birkeland电流）从这个等离子体边界向下流到电离层。产生电流的机制基本上是Alfven在1939年最初提出的。在阿尔芬层中产生一定量的电荷分离，因为离子和电子的地心漂移路径在层内不重合。电荷分离产生垂直于B的电场，并沿沿着力线传输到电离层。电流流过电离层中的磁场线，并沿着磁场线流向阿尔芬层。电场被这些电流减小，这些电流流动以中和电荷分离。阿尔芬层的位置是这样的，以产生一个电流片，进入电离层在极光纬度。据计算，中和阿尔芬层所需的伯克兰电流约为106安培，这足以产生约100 γ的横向磁扰动，这些横向磁扰动已被极光纬度的卫星观测到;阿尔芬层的厚度对应于这些横向磁扰动带的宽度。最后，伯克兰电流与包括DS电流系统在内的更大电流系统有关。
Energetic plasma drifting toward the earth from the plasma sheet in the earth's magnetospheric tail is terminated by an inner boundary (the Alfven layer). Sheets of field-aligned current (Birkeland currents) flow down to the ionosphere from this plasma boundary. The mechanism for generating the current is essentially that originally proposed by Alfven in 1939. A certain amount of charge separation develops in the Alfven layer because the geocentric drift paths of ions and electrons are not coincident within the layer. The charge separation produces an electric field that is perpendicular to B and is transmitted along lines of force to the ionosphere. Currents flow across magnetic field lines in the ionosphere and along the magnetic field lines to the Alfven layer. The electric field is reduced by these currents, which flow to neutralize the charge separation. The position of the Alfven layer is such as to produce a current sheet that enters the ionosphere at auroral latitudes. The Birkeland current necessary to neutralize the Alfven layer is calculated to be about 106 amps, which is sufficient to produce the transverse magnetic disturbances of about 100 γ that have been observed by satellites in auroral latitudes; the thickness of the Alfven layer corresponds to the width of the zone of these transverse magnetic disturbances. Finally, the Birkeland current is related to a larger current system that includes the DS current system.