Ohtani S, Motoba T, Gjerloev J W, Frey H U, Mann I R, Chi P J, Korth H
Johns Hopkins University Applied Physics Laboratory Laurel MD USA.
Space Sciences Laboratory University of California Berkeley CA USA.
J Geophys Res Space Phys. 2022 Jun;127(6):e2021JA030114. doi: 10.1029/2021JA030114. Epub 2022 Jun 9.
In the present study we examine three substorm events, Events 1-3, focusing on the spatio-temporal development of auroral electrojets (AEJs) before auroral breakup. In Events 1 and 2, auroral breakup was preceded by the equatorward motion of an auroral form, and the ground magnetic field changed northward and southward in the west and east of the expected equatorward flow, respectively. Provided that these magnetic disturbances were caused by local ionospheric Hall currents, this feature suggests that the equatorward flow turned both eastward and westward as it reached the equatorward part of the auroral oval. The auroral breakup took place at the eastward-turning and westward-turning branches in Events 1 and 2, respectively, and after the auroral breakup, the westward AEJ enhanced only on the same side of the flow demarcation meridian. The zonal flow divergence is considered as an ionospheric manifestation of the braking of an earthward flow burst in the near-Earth plasma sheet and subsequent dawnward and duskward turning. Therefore, in Events 1 and 2, the auroral breakup presumably mapped to the dawnward and duskward flow branches, respectively. Moreover, for Event 3, we do not find any pre-onset auroral or magnetic features that can be associated with an equatorward flow. These findings suggest that the braking of a pre-onset earthward flow burst itself is not the direct cause of substorm onset, and therefore, the wedge current system that forms at substorm onset is distinct from the one that is considered to form as a consequence of the flow braking.
在本研究中，我们考察了3次亚暴事件（事件1 - 3），重点关注极光破裂前极光电集流（AEJs）的时空发展。在事件1和事件2中，极光破裂之前有一种极光形态向赤道方向移动，地面磁场在预期赤道向流动的西侧向北变化，在东侧向南变化。假设这些磁扰动是由局部电离层霍尔电流引起的，这一特征表明赤道向流动在到达极光椭圆的赤道部分时既向东也向西转向。在事件1和事件2中，极光破裂分别发生在向东转向和向西转向的分支处，极光破裂之后，向西的AEJ仅在流动分界子午线的同一侧增强。纬向流散度被认为是近地等离子体片中向地球方向流动爆发的制动以及随后向黎明和黄昏方向转向的电离层表现。因此，在事件1和事件2中，极光破裂大概分别对应于向黎明和黄昏方向的流动分支。此外，对于事件3，我们没有发现任何可以与赤道向流动相关联的爆发前极光或磁特征。这些发现表明，爆发前向地球方向流动爆发的制动本身不是亚暴起始的直接原因，因此，在亚暴起始时形成的楔形电流系统与被认为是由流动制动产生的楔形电流系统不同。
