Abstract 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 RE downtail, 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.

中文翻译：

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亚风暴的发生和发展：流动通道的关键作用

摘要 在本文中，我们描述了我们在过去 10 年的研究中开发的亚暴扩展阶段情景的基本特征和观测基础。起始沿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，沿着起始极光弧呈珠状，该弧位于极光椭圆的赤道边界附近。这些起始波和大振幅电场振荡的增长表明从稳定状态到不稳定状态的突然转变导致了起始。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，导致向不稳定性转变，并且这种流动爆发在极光椭圆形中被标记为极地边界增强（PBI）的开始，它演变成极光流光。与这些和其他 PBI 相关的等离子体流通常与遥远的尾部中线处增强的重新连接有关，重新连接是由来自极冠的进入流动通道触发的。起始不稳定性是由侵入的熵减等离子体突然改变内部等离子体片中的熵分布引发的，尽管尚未确定具体的起始不稳定性。起始不稳定性在方位角上对齐并在方位角上扩展，这是因为当气泡向地球移动时，低能量离子倾向于跟随电场向黎明侧漂移，而高能量离子磁力向黄昏侧漂移。因此，熵沿质心漂移轨迹不守恒，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拖缆。这是如何发生的另一个主要悬而未决的问题，但第一批拖缆可能会在等离子片 ∼20 RE 下端开始，据推测该区域在发生后不久就会发生重新连接。一旦扩展阶段的极光活动到达极光极地边界，拖缆及其相关联的重新连接很可能在遥远的尾部中线处开始。