Formation and release of the Harang reversal relating with the substorm onset process
Formation and release of the Harang reversal relating with the substorm onset process
复制标题
与亚暴爆发过程相关的哈朗反转的形成和释放
DOI：
10.1029/2020ja028170
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发表时间：
2021
期刊：
影响因子：
--
通讯作者：
R.
中科院分区：
文献类型：
--
作者：
Tanaka;T.;Ebihara;Y.;Watanabe;M.;Den;M.;Fujita;S.;Kikuchi;T.;Hashimoto;K. K. ;and Kataoka;R.
随着行星际磁场（IMF）由北向南转变，全球模拟先后再现了亚暴的生长阶段、起始阶段和扩展阶段。计算的电离层对流生长期重现了观测到的Harang反转（HR）、向上场向电流（FAC）的发展和即将到来的起始点。从夜侧中心向上的磁场线是开放的，而从起始点向上的磁场线是封闭的。这些开放的磁场线映射出在O/C边界外的流动剪切。从磁组态看，生长阶段是零的替换过程。两个新的空区出现在南侧IMF下方的昼侧，而两个旧的空区出现在北侧IMF下方，在黎明和黄昏侧形成两个分叉区域。O/C边界附近的流切变是由磁层对流形成的，磁层对流通过分岔区返回昼侧。膨胀阶段通过近地中性线（NENL）的拓扑变化进行。NENL发生在北向IMF残余物的变薄结构内部，在流动切变的低纬度一侧，并向下投射到向上FAC的低纬度边缘。与NENL相关的是，对流返回路径改变到等离子体片的中心，并在电离层中以HR的释放形式显示出来。在电离层中，由于磁场线的收缩，O/C边界向极地迁移。
With the interplanetary magnetic field (IMF) that turns from northward to southward, the global simulation successively reproduces the growth phase, the onset, and the expansion phase of the substorm. The calculated ionospheric convection for the growth phase reproduces the development of the Harang reversal (HR), the upward field‐aligned current (FAC), and the upcoming onset point as observed. Magnetic field lines traced from the center of the nightside upward FAC are open, while the magnetic field line traced from the onset point is closed. These open magnetic field lines map to flow shear just outside the O/C boundary. Seen from the magnetic configuration, the growth phase proceeds as the replacement process of nulls. Two new nulls appear on the dayside under the southward IMF, while two old nulls under the northward IMF retreat tailward forming two bifurcation regions on the dawn and dusk flanks. Flow shear around the O/C boundary forms by magnetospheric convection that returns to the dayside via bifurcation regions. The expansion phase proceeds through a topological change by the near‐earth neutral line (NENL). The NENL occurs inside the thinned structure of the northward IMF remnant, on the low‐latitude side of the flow shear, and projects down to the low‐latitude edge of the upward FAC. Associated with the NENL, the convection return path changes to the center of the plasma sheet and reveals in the ionosphere as the release of the HR. By the shrinkage of projecting magnetic field line, the O/C boundary migrates poleward in the ionosphere.