Counter equatorial electrojet and overshielding after substorm onset: Global MHD simulation study
Counter equatorial electrojet and overshielding after substorm onset: Global MHD simulation study
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DOI：
10.1002/2014ja020065
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发表时间：
2014-09
期刊：
影响因子：
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通讯作者：
Yusuke Ebihara;T. Tanaka;T. Kikuchi
中科院分区：
文献类型：
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作者：
Yusuke Ebihara;T. Tanaka;T. Kikuchi
通过全球磁流体动力学（MHD）模拟，我们首次证明了在亚暴发生后，在没有行星际磁场向北转向的情况下，日侧磁赤道的电喷流可以逆转，并且可以在内磁层建立过屏蔽条件。在亚暴发生附近，等离子体压力在夜侧的内磁层中高度增强。第2区磁场对准的电流与高压区日侧延伸表面的抗磁电流不同，高压区与电离层相连，电离层位于电离层相对较低的电离层，电离层位于主极光椭圆的赤道方向几度处，主极光椭圆形是等离子体片的投影。极光区赤道边界和第2区电流赤道边界的分离导致黄昏-黎明电场在日侧磁赤道产生反电喷流（CEJ）。在较窄的纬向宽度内，向极电场同时增强，可视为亚极光离子漂移和亚极光极化流。黄昏-黎明电场可能沿场线以剪切alfvsamn波的形式传播到内磁层。然后，内磁层完全受到过屏蔽条件的约束。CEJ的强度和极性在很大程度上至少取决于与等离子体压力相关的电离层电导率（可能与漫射极光有关）。这可以解释过度屏蔽并不总是在发病后发生的观察事实。
By performing a global magnetohydrodynamic (MHD) simulation, we have demonstrated for the first time that an electrojet at the dayside magnetic equator can be reversed and an overshielding condition can be established in the inner magnetosphere after substorm onset without northward turning of the interplanetary magnetic field. Near the substorm onset, the plasma pressure is highly enhanced in the inner magnetosphere on the nightside. The Region 2 field‐aligned current diverges from the diamagnetic current on the surface of the dayside extension of the high‐pressure region, which is connected to the ionosphere in the relatively low‐conductivity region a few degrees equatorward of the main auroral oval that is formed as the projection of the plasma sheet. The separation of the equatorward boundary of the auroral region and the equatorward boundary of the Region 2 current results in dusk‐dawn electric fields that generate a counter electrojet (CEJ) at the dayside magnetic equator. Poleward electric fields in a narrow latitudinal width, which may be regarded as subauroral ion drift and subauroral polarization stream, are simultaneously intensified. The dusk‐dawn electric fields may propagate to the inner magnetosphere along a field line as shear Alfvén waves. Then, the inner magnetosphere is completely constrained by the overshielding condition. The intensity and polarity of the CEJ depend largely on at least the ionospheric conductivity that is related to the plasma pressure (probably associated with diffuse aurora). This may explain the observational fact that overshielding does not always occur after onset.