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Magnetosphere-Ionosphere Coupling Feedback Instability for Substorm Generation by Dr. Wladislaw Lyatsky 29 June 2001 Although the idea that substorm generation may be a result of a magnetosphere-ionosphere coupling feedback instability was proposed a long ago, a specific mechanism showing how it can work was found only recently. Substorm generation can be described as a strong and fast increase in the magnitude of upward field-aligned currents in the nightside auroral zone, which are responsible for acceleration of precipitating particles that is one of most evident features of substorms. Since field-aligned currents close ionospheric currents, their magnitude is controlled by ionospheric conductivity. Before a substorm, nightside ionospheric conductivity is small and field-aligned currents are weak. Increasing the polar cap electric field leads to an increase in field-aligned currents. When their magnitude becomes sufficiently large to accelerate precipitating electrons, a feedback mechanism becomes possible. Precipitating electrons, associated with upward field-aligned current, increase the ionospheric conductivity, which in turn leads to a further increase in field-aligned currents. This stimulates an explosion-like increase in field-aligned currents that leads to a strong energy release in the nightside ionosphere and substorm onset.
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