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On the coupling of fast and shear Alfvén wave modes by the ionospheric hall conductance

机译：电离层霍尔电导耦合快和剪切Alfvén波模

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摘要

There are two low frequency,magnetised,cold plasma wave modes that propagate through the Earth's magnetosphere. These are the compressional (fast) and the shear Alfvén modes. The fast mode distributes energy throughout the magnetosphere with the ability to propagate across the magnetic field. Previous studies of coupling between these two modes have often focussed on conditions necessary for mode coupling to occur in the magnetosphere. However,Kato and Tamao (1956) predicted mode coupling would occur for non-zero Hall currents. Recently,the importance of the Hall conductance in the ionosphere for low frequency wave propagation has been studied using one dimensional (1-D) models. In this paper we describe effects of the ionosphere Hall conductance on field line resonance and higher frequency, 0.1-5 Hz waves associated with the Ionospheric Alfvén Resonator (IAR). The Hall conductance reduces the damping time of field line resonances and Joule dissipation into the ionosphere. The Hall conductance also couples shear Alfvén waves trapped in the IAR to fast mode waves that propagate across the ambient magnetic field in an ionospheric waveguide. This coupling leads to the production of low frequency magnetic fields on the ground that can be observed by magnetometers.
机译：有两种低频，磁化的冷等离子体波模式，它们在地球磁层中传播。这些是压缩（快速）和剪切Alfvén模式。快速模式将能量分配到整个磁层，并具有在磁场中传播的能力。先前对这两种模式之间耦合的研究通常集中在磁层中发生模式耦合所需的条件上。但是，Kato和Tamao（1956）预测非零霍尔电流会发生模式耦合。近来，已经使用一维（1-D）模型研究了电离层中霍尔电导对于低频波传播的重要性。在本文中，我们描述了电离层霍尔电导对场线谐振和与电离层Alfvén谐振器（IAR）相关的更高频率的0.1-5 Hz波的影响。霍尔电导减少了场线共振的阻尼时间以及焦耳耗散到电离层中的时间。霍尔电导还将耦合在IAR中的Alfvén剪切波耦合到在电离层波导中传播穿过环境磁场的快速模式波。这种耦合导致在地面上产生低频磁场，可以通过磁力计观察到。

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