Substorm triggering by new plasma intrusion: Incoherent‐scatter radar observations
Substorm triggering by new plasma intrusion: Incoherent‐scatter radar observations
复制标题
DOI：
10.1029/2009ja015168
复制
发表时间：
2010-07
影响因子：
--
通讯作者：
L. Lyons;Y. Nishimura;Y. Shi;S. Zou;Hwajin Kim;V. Angelopoulos;C. Heinselman;M. Nicolls;K. Fornacon
中科院分区：
文献类型：
--
作者：
L. Lyons;Y. Nishimura;Y. Shi;S. Zou;Hwajin Kim;V. Angelopoulos;C. Heinselman;M. Nicolls;K. Fornacon
2009 年 12 月 4 日收到； 2010 年 3 月 16 日修订； 2010 年 3 月 30 日接受； 2010 年 7 月 27 日发表。 [1] 在配套论文中，我们在 THEMIS 全天成像仪观测中确定了导致亚暴爆发的一系列可重复事件：增强的气流将新的等离子体带入等离子体片。然后，新的等离子体作为流动通道向地球移动，将其带到近地等离子体片并在那里产生不稳定。进入黄昏（黎明）对流细胞的新等离子体向赤道和向东漂移，然后围绕哈朗反转，导致午夜前（接近午夜和午夜后）爆发。在这里，我们使用非相干散射雷达（ISR）电离层观测提供支持该序列的证据。使用 Sondrestrom ISR，我们发现增强的新血浆流通常在开始前约 8 分钟从极帽进入血浆片。这些流动与极地边界增强特征有关，与成像仪的推论一致。使用扑克平地ISR（PFISR），我们发现在爆发前不久，增强的西向气流到达哈朗反转赤道方向的亚极光偏振流（SAPS）区域（黄昏单元爆发），或者增强的东向气流从极地方向进入爆发区域（黎明单元爆发）。 PFISR 质子沉淀特征与以下可能性一致：增强的流由熵减的等离子体片状等离子体组成，并且起始点发生在大部分增强的 SAPS 流的极地（黄昏细胞起始点）或增强的向东流的赤道方向（黎明细胞起始点）。与降低熵等离子体的一致性仅在增强流中可见，这使我们认为低熵等离子体的侵入可能会改变熵的径向梯度，从而导致不稳定。
Received 4 December 2009; revised 16 March 2010; accepted 30 March 2010; published 27 July 2010. [1] In the companion paper, we identified a repeatable sequence of events leading to substorm onset in THEMIS all‐sky imager observations: enhanced flows bring new plasma into the plasma sheet. The new plasma then moves earthward as a flow channel, bringing it to the near‐Earth plasma sheet and where it produces onset instability. New plasma entering the dusk (dawn) convection cell drifts equatorward and eastward and then around the Harang reversal, leading to pre‐midnight (near‐ and post‐midnight) onset. Here we present evidence supporting this sequence using incoherent scatter radar (ISR) ionospheric observations. Using the Sondrestrom ISR, we find that enhanced flows of new plasma commonly enter the plasma sheet from the polar cap ∼8 min prior to onset. These flows are related to poleward boundary intensification signatures, consistent with the inferences from the imagers. Using the Poker Flat ISR (PFISR), we find that shortly before onset, enhanced westward flows reach the subauroral polarization streams (SAPS) region equatorward of the Harang reversal (dusk‐cell onsets) or enhanced eastward flows enter the onset region from the poleward direction (dawn‐cell onset). PFISR proton precipitation signatures are consistent with the possibility that the enhanced flows consist of reduced‐entropy plasma sheet plasma, and that onset occurs poleward of much of the enhanced SAPS flow (dusk‐cell onsets) or equatorward of the enhanced eastward flows (dawn‐cell onsets). Consistency with reduced entropy plasma is seen only within the enhanced flows, leading us to suggest that intrusion of low‐entropy plasma may alter the radial gradient of entropy toward onset instability.