来自重联霍尔区的向下极光流
Downward auroral currents from the reconnection Hall-region
摘要：
我们提出了一个简单的（固定）机制，能够产生极光向下场对齐的电场{这是}需要{加速电离层电子成分进入磁层和限制电离层离子在低纬度（如所需的观测电离层空腔在向下的极光电流区域）。上升的电离层电子携带着向下的极光流。我们的模型基于尾电流片中无碰撞重联的假设。它利用了重联{ \sf X}线周围离子惯性区中电子和离子之间的动力学差异，从而导致霍尔电流流动。我们表明，霍尔磁场和通量的空间约束的离子惯性区域为中心的{ \sf X}-点产生的空间可变电动势，这是积极的离子惯性区域的外流入边界附近和负的中央流入区域。从电离层看，它的功能就像一个局部的中尺度电势。正电动势引起电离层向上的电子流{在亚暴期间（造成`黑色极光'）}。一个类似的正电位被确定在地球一侧的快速重联流出区域，具有相同的效果，解释了观察，极光向上的电流两侧的狭窄向下的电流。关键词{场向极光流，平行场，重联中的霍尔场，亚暴}
英文摘要：
We present a simple (stationary) mechanism capable of generating the auroral downward field-aligned electric field {that is} needed for {accelerating the ionospheric electron component up into the magnetosphere and confining the ionospheric ions at low latitudes (as is required by observation of an ionospheric cavity in the downward auroral current region). The lifted ionospheric electrons carry the downward auroral current. Our model is based on the assumption of collisionless reconnection in the tail current sheet. It makes use of the dynamical difference between electrons and ions in the ion inertial region surrounding the reconnection {\sf X}-line which causes Hall currents to flow. We show that the spatial confinement of the Hall magnetic field and flux to the ion inertial region centred on the {\sf X}-point generates a spatially variable electromotive force which is positive near the outer inflow boundaries of the ion inertial region and negative in the central inflow region. Looked {at} from the ionosphere it functions like a localised meso-scale electric potential.} The positive electromotive force gives rise to upward electron flow from the ionosphere {during substorms (causing `black aurorae')}. A similar positive potential is identified on the earthward side of the fast reconnection outflow region which has the same effect, explaining the observation that auroral upward currents are flanked from both sides by narrow downward currents. keywords{Field-aligned auroral currents, parallel fields, Hall field in reconnection, substorms}
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