Abstract

This paper analyzes the role of the outer ionosphere in the occurrence of a large difference in the frequency of accelerated electron fluxes in the auroral region in the premidnight sector for winter and summer conditions, which are associated with discrete auroras. Simulation indicates that the critical value J_EIC of the longitudinal current of the Alfvén wave for the development of electrostatic ion–cyclotron instability at heights around the Earth’s radius (h ~ R_E) for winter almost coincides with the upper limit of average values of the stationary large-scale longitudinal current. Therefore, weak fluctuations of the longitudinal current associated with the Alfvén wave are sufficient in winter for the development of processes leading to accelerated electron fluxes, which are associated with discrete auroras. The summer value of J_EIC is four to five times higher than that for winter, and a stimulated precipitation of auroral electrons is likely to be possible only at high geomagnetic activity. The winter/summer asymmetry in the J_EIC value is mainly associated with specific changes in the parameters of the outer ionosphere along the geomagnetic field. The difference in electron density reaches a maximum at heights h ~ R_E, where the summer values of this density are five to six times higher than the winter ones, which, in turn, is associated with higher summer temperatures of electrons and ions. The important role of these temperatures in the winter/summer asymmetry in the frequency of accelerated electrons has been noted, it would seem, for the first time.

中文翻译：

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外电离层在极光电子降水的冬/夏季不对称中的作用

摘要

本文分析了电离层在冬季和夏季条件下午夜前的极光区域中加速电子通量频率出现较大差异时的作用，这与离散的极光有关。模拟结果表明，临界值Ĵ _EIC在围绕地球的半径（高度阿尔芬波的静电离子回旋不稳定性的发展的纵向电流ħ〜ř _Ë）几乎与固定的大型纵向电流平均值的上限一致。因此，在冬季，与Alfvén波有关的纵向电流的微弱波动足以形成导致加速电子通量的过程，而电子通量的增加与离散的极光有关。J _EIC的夏季值是冬季的四到五倍，只有在高地磁活动下，极光电子的刺激沉淀才有可能。在冬季/夏季不对称Ĵ _EIC值主要与沿地球磁场的外电离层的参数的特定的变化相关联。电子密度的差异在高度处达到最大值ħ〜ř _é，其中该密度的夏季值大于冬天的，这反过来，与电子和离子的夏季气温较高相关联的更高的五到六倍。似乎第一次注意到了这些温度在冬/夏不对称性中对加速电子的频率的重要作用。