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Effects of the active auroral ionosphere on magnetosphere - ionosphere coupling.

机译:活跃的极光电离层对磁层-电离层耦合的影响。

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The thesis is devoted to the effects of electromagnetic coupling between the Earth's magnetosphere and the active auroral ionosphere. The research has been focused, in particular, on the concept of ionospheric feedback instability. The feedback instability arises when localized perturbations in ionospheric conductivity become polarized in the presence of background electric field. Under favorable conditions of low ionospheric conductivity and strong electric convection the development of ionospheric feedback instability leads to the generation of magnetospheric ULF pulsations and precipitation of energetic particles into the auroral ionosphere that produce visible glow in the sky known as aurora. Numerical studies of magnetosphere-ionosphere coupling have been performed using a model that includes active ionospheric feedback and shear Alfvén wave dynamics of the magnetospheric response. Strong parallel inhomogeneities of the magnetospheric parameters included in the numerical model permit the simultaneous development of local ionospheric resonator modes (fast feedback) trapped between the ionosphere and Alfvén speed maximum above it and field line eigenmodes (slow feedback) that stand along the entire magnetic field line between two conjugate ionospheres. Effects of plasma anomalous resistivity in the large field-aligned currents of the feedback-driven Alfvén waves generate fluxes of energetic electrons that precipitate into the ionosphere producing auroral luminosity. The results of these simulations provide insights into the magnetospheric processes that cause the precipitation and allow us to estimate the precipitating electron energy flux for given ambient conditions. Numerical analysis of the effects of seasonal asymmetry in the ionospheric conductivity suggest that the feedback instability can be responsible for higher occurrence of auroral arcs in dark winter hemisphere as demonstrated by satellite observations. Simulations of the heating effects imposed on the auroral ionosphere by powerful radio waves suggest that the feedback instability can be excited artificially by HF radars. The results of numerical modeling demonstrate an agreement with satellite observations of the Alfvén waves and electron fluxes registered during experiments of modulated heating of the auroral electrojet.
机译:本文致力于地球磁层与活跃极光电离层之间的电磁耦合作用。该研究尤其集中在电离层反馈不稳定性的概念上。当电离层电导率中的局部扰动在背景电场存在下被极化时,就会出现反馈不稳定性。在低电离层电导率和强对流的有利条件下,电离层反馈不稳定的发展会导致磁层ULF脉动的产生,以及高能粒子向极光电离层中的沉淀,从而在天空中产生称为“极光”的可见光。已经使用包括主动电离层反馈和磁层响应的切变Alfvén波动力学在内的模型对磁层-电离层耦合进行了数值研究。数值模型中所包含的磁层参数的强平行不均匀性允许同时开发陷于电离层和高于其的Alfvén速度最大值之间的局域电离层谐振器模式(快速反馈)以及沿整个磁场站立的场线本征模式(缓慢反馈)两个共轭电离层之间的直线。在反馈驱动的Alfvén波的大场对准电流中,等离子体异常电阻率的影响会产生高能电子通量,该高能电子通量沉淀到电离层中,产生极光。这些模拟的结果提供了对引起降水的磁层过程的见解,并允许我们在给定的环境条件下估计正在沉淀的电子能通量。季节性不对称对电离层电导率影响的数值分析表明,如卫星观测所示,反馈的不稳定性可能是冬季暗半球极光弧发生率更高的原因。对强无线电波施加到极光电离层上的加热效果的模拟表明,HF雷达可以人为地激发反馈的不稳定性。数值模拟的结果表明,与对极光电喷的调制加热实验期间记录的Alfvén波和电子通量的卫星观测结果一致。

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