Substorms: Fundamental observational features, distinction from other disturbances, and external triggering
Substorms: Fundamental observational features, distinction from other disturbances, and external triggering
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DOI：
10.1029/95ja01987
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发表时间：
1996-06
期刊：
影响因子：
--
通讯作者：
L. Lyons
中科院分区：
文献类型：
--
作者：
L. Lyons
本文综述了亚暴和其他极光带扰动的基本观测特征。结果表明，在极光区至少发现了三种不同类型的主要地磁扰动，并建议在得出有关亚暴的观测结论时，应注意将亚暴与其他类型的扰动区分开来。亚暴可以通过电流楔的形成和相关的西向电喷流以及在膨胀阶段在电离层内向极地移动的活跃极光区域来唯一地识别。已经观察到，只要行星际磁场（IMF）稳定地向南移动，在没有亚暴的情况下，对流增强的周期就会继续存在。它们的AL特征看起来很像强烈的亚暴，但这些特征是由增强的对流驱动的强大的DP 2电离层电流造成的，而不是来自夜间向西的电喷流。第三种扰动的特点是电离层内向赤道方向流动的短间隔增强和极光发射的增强。这些增强从极帽边界附近向赤道移动，并且它们可能与等离子体片内向地球流动的几分钟长的增强有关。本文还回顾了有关国际货币基金组织变化引发次暴扩张的研究。将亚暴与其他扰动区分开来，这些研究表明，大多数，也许是所有的膨胀都是由IMF的变化引发的。这些变化包括向北的转向和y分量的减小。如果大多数亚暴确实是由外部触发的，那么亚暴通常不是由内部磁层不稳定引起的。
Fundamental observational signatures of substorms and other auroral zone disturbances are summarized in this review. It is shown that at least three distinct types of major geomagnetic disturbance have been identified in the auroral zones, and it is suggested that care should be taken in distinguishing substorms from the other types of disturbance when reaching observational conclusions concerning substorms. Substorms can be uniquely identified by the formation of the current wedge and by the associated westward electrojet and region of active aurora that move poleward within the ionosphere during the expansion phase. Periods of enhanced convection have been observed to continue without substorms for as long as the interplanetary magnetic field (IMF) remains stably southward. They can have AL signatures that look very much like intense substorms, but these signatures result from strong DP 2 ionospheric currents driven by enhanced convection rather than from a nightside, westward electrojet. A third type of disturbance is characterized by short intervals of enhanced equatorward flow within the ionosphere and enhanced auroral emissions. These enhancements move equatorward from near the polar cap boundary, and they may be associated with several‐minute‐long enhancements of earthward flow within the plasma sheet. Studies that have examined the triggering of substorm expansions by IMF changes are also reviewed. When considered together, and substorms are distinguished from the other disturbances, these studies imply that most, and perhaps all, expansions are triggered by IMF changes. These changes include both northward turnings and reductions in the magnitude of the y component. If most substorms are indeed externally triggered as suggested here, then substorms must generally not be the result of an internal magnetospheric instability.