Substorm onset and development: The crucial role of flow channels
Substorm onset and development: The crucial role of flow channels
复制标题
DOI：
10.1016/j.jastp.2020.105474
复制
发表时间：
2020-10
影响因子：
1.9
通讯作者：
L. Lyons;Y. Nishimura
中科院分区：
文献类型：
--
作者：
L. Lyons;Y. Nishimura
在本文中，我们描述了我们在过去约 10 年的研究中得出的亚暴扩展阶段情景的基本特征和观测基础。起始点沿着内部质子等离子体片的磁场线发生，并且首先在极光中看到为沿着起始极光弧的串珠，该极光弧位于极光椭圆形的赤道边界附近。这些起始波的增长和大幅度电场振荡表明从稳定状态到不稳定状态的突然转变导致了起始。向不稳定的转变是由于低熵流爆发/通道（即等离子体气泡）侵入内部等离子体片而发生的，并且这种流爆发在极光椭圆形中通过向极地边界增强（PBI）的启动而被标记，并演变成极光流光。与这些和其他 PBI 相关的等离子体流通常与远处尾部中性线处的增强重连接相关，该重连接由来自极帽的传入流通道触发。尽管具体的起始不稳定性尚未确定，但起始不稳定性是由侵入的减熵等离子体突然改变内部等离子体片中的熵分布而引发的，这是合理的。起始不稳定性是方位角对齐并沿方位角扩展，这是因为当气泡向地球移动时，较低能量的离子倾向于跟随电场向黎明一侧漂移，而较高能量的离子磁力向黄昏一侧漂移。因此，沿着质心漂移轨迹，熵不守恒，并且气泡沿经度扩散并加深。不断增长的起始波向非线性的过渡导致了流光。这是如何发生的是另一个主要的悬而未决的问题，但第一个流光可能在血浆片〜20 REdowntail内启动，该区域被推断在发生后不久就会发生重新连接。一旦扩张阶段的极光活动到达极光极向边界，流光及其相关的重新连接很可能在遥远的尾部中性线开始。亚暴流楔由一系列与膨胀相拖缆相关的纵向局部流动爆发区域（楔形）形成，使局部磁场两极化，并在地面上产生传统的地面爆发特征，即极光区 H 湾和中纬度正 H 湾和 Pi2 脉动。
In this paper, we described the basic features and observations bases of the scenario for the substorm expansion phase that we have developed from our research over the past ~10 years. Onset occurs along magnetic field lines of the inner proton plasma sheet, and is first seen in the aurora as beading along the onset aurora arc, which lies near the equatorward boundary of the auroral oval. Growth of these onset waves and large amplitude electric field oscillations indicates that an abrupt transition from a stable to unstable state leads to onset. The transition to instability occurs as a result of an intrusion of a low-entropy flow burst/channel (i.e., a plasma bubble) to the inner plasma sheet, and such flow bursts are marked in the auroral oval by the initiation of a poleward boundary intensification (PBI) that evolves into an auroral streamer. Plasma flows associated with these and other PBIs are generally associated with enhanced reconnection at the distant tail neutral line, the reconnection being triggered by an incoming flow channel from the polar cap. It is reasonable that the onset instability is triggered by the intruding reduced entropy plasma abruptly changing the entropy distribution in the inner plasma sheet, though the specific onset instability has not been identified. The onset instability is azimuthally aligned and expands azimuthally, these occurring because, as a bubble moves earthward, lower energy ions tending to follow the electric field drift towards the dawn side while higher energy ions magnetic drift towards the duskside. Thus entropy is not conserved along center of mass drift trajectories, and the bubble spreads in longitude and deepens. The transition to non-linearity of the growing onset waves leads to streamers. How this occurs is another major outstanding question, but the first streamers could initiate within the plasma sheet ~20 REdowntail, the region where reconnection has been inferred to occur soon after onset. It is likely that streamers and their associated reconnection initiate at the distant tail neutral line once the expansion phase auroral activity reaches the auroral poleward boundary. The substorm current wedge builds up from a sequence of longitudinally localized flow burst regions (wedgelets) that are associated with the expansion-phase streamers, dipolarize the local magnetic field, and give rise to traditional ground onset signatures on the ground, namely auroral zone H bays and mid-latitude positive H bays and Pi2 pulsations.