Suppression of discrete aurorae by sunlight
Suppression of discrete aurorae by sunlight
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DOI：
10.1038/381766a0
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发表时间：
1996-06-27
期刊：
影响因子：
64.8
通讯作者：
Lyons, KM
中科院分区：
文献类型：
--
作者：
Newell, PT;Meng, CI;Lyons, KM
长期以来，人们一直认为极光就像恒星一样，存在于白天，但被天空表面的高亮度所掩盖，最亮的极光是由地球磁层中加速的电子束产生的离散的光幕。已经提出了许多理论来解释离散极光，但与最近的观测结果最匹配的理论(2)调用了通过注入电子而增强的电离层电导率与这些相同电子携带的电流之间的正反馈机制(3-5)。本文利用气象卫星九年的带电粒子资料对电子降水事件进行了统计研究。我们发现，引起离散极光的加速电子束主要发生在黑暗中：冬半球比夏半球更好，夜间比白天更好。我们还发现，在弥散极光的存在下，离散极光很少发生，扩散极光提供了足够的传导性来支持磁层和电离层之间的电流。综上所述，这些观测结果有力地支持了电离层电导率是控制离散极光发生的关键因素的观点。
IT HAS long been assumed that aurorae, like stars, are present during daylight, but hidden by the high surface brightness of the sky, The brightest aurorae are discrete curtains of light created by beams of electrons accelerated in the Earth's magnetosphere. Many theories' have been proposed to explain discrete aurorae, but the one that provides the best match to recent observations(2) invokes a positive feedback mechanism between the conductivity of the ionosphere, which is enhanced by the injection of electrons, and the current carried by these same electrons(3-5). Here we present a statistical study of electron precipitation events by using nine years of charged-particle data from weather satellites, We find that the beams of accelerated electrons that cause the discrete aurorae occur mainly in darkness: the winter hemisphere is favoured over the summer hemisphere, and night is favoured over day. We also find that discrete aurorae rarely occur in the presence of diffuse aurorae, which provide sufficient conductivity to support the electric currents between the magnetosphere and the ionosphere. Taken together, these observations strongly support the view that ionospheric conductivity is the key factor controlling the occurrence of discrete aurorae.