Comment on “Tail Reconnection Triggering Substorm Onset”

Lui, A. T. Y.

doi:10.1126/science.1167726

Cited by 64 publications

(60 citation statements)

References 18 publications

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“…Angelopoulos 2008) or via current disruption leading to reconnection subsequently (e.g. Lui 2009). Indeed, these could be independent regions being activated independently (e.g.…”

Section: Discussionmentioning

confidence: 99%

Using ultra-low frequency waves and their characteristics to diagnose key physics of substorm onset

et al. 2017

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Substorm onset is marked in the ionosphere by the sudden brightening of an existing auroral arc or the creation of a new auroral arc. Also present is the formation of auroral beads, proposed to play a key role in the detonation of the substorm, as well as the development of the large-scale substorm current wedge (SCW), invoked to carry the current diversion. Both these phenomena, auroral beads and the SCW, have been intimately related to ultra-low frequency (ULF) waves of specific frequencies as observed by ground-based magnetometers. We present a case study of the absolute and relative timing of Pi1 and Pi2 ULF wave bands with regard to a small substorm expansion phase onset. We find that there is both a location and frequency dependence for the onset of ULF waves. A clear epicentre is observed in specific wave frequencies concurrent with the brightening of the substorm onset arc and the presence of "auroral beads". At higher and lower wave frequencies, different epicentre patterns are revealed, which we conclude demonstrate different characteristics of the onset process; at higher frequencies, this epicentre may demonstrate phase mixing, and at intermediate and lower frequencies these epicentres are characteristic of auroral beads and cold plasma approximation of the "Tamao travel time" from near-earth neutral line reconnection and formation of the SCW.

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“…Angelopoulos 2008) or via current disruption leading to reconnection subsequently (e.g. Lui 2009). Indeed, these could be independent regions being activated independently (e.g.…”

Section: Discussionmentioning

confidence: 99%

Using ultra-low frequency waves and their characteristics to diagnose key physics of substorm onset

et al. 2017

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“…The substorm onset triggering mechanism has been a key question since the beginning of substorm research, but general agreement on the timing sequence leading to substorm onset has yet to reach a conclusive agreement despite over 40 years of debate [e.g., McPherron et al , 1973; Angelopoulos et al , 2008; Lui , 2008]. Recently, Nishimura et al [2010a], Lyons et al [2010], and Xing et al [2010] presented evidence for a new idea of the preonset sequence starting with a poleward boundary intensification (PBI) associated with local reconnection occurring near the magnetic separatrix.…”

Section: Introductionmentioning

confidence: 99%

Near-Earth plasma sheet azimuthal pressure gradient and associated auroral development soon before substorm onset

et al. 2011

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[1] The azimuthal plasma pressure gradient in the near-Earth plasma sheet makes crucial contributions to field-aligned current (FAC) formation. Numerical simulations and statistical observations have shown that a plasma pressure peak tends to build up in the premidnight region of the near-Earth plasma sheet during the substorm growth phase owing to enhanced magnetic drift. This leads to azimuthal pressure gradients in this region. The temporal variation of the azimuthal pressure gradient may provide an indication for the FAC variations associated with the substorm growth phase and may set up a plasma sheet precondition for the substorm onset being triggered near this region. We take advantage of two of the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft separated azimuthally near the orbit apogee and investigate the azimuthal plasma pressure gradient before substorm onset in the R ∼10-12 R E region. Equatorial plasma pressure is estimated by removing the curvature force effect. Five events with the spacecraft footprints mapped very close to the aurora onset region were selected. These events show substantial duskward pressure gradient enhancement 1-5 min before onset. The onset arc, which results from enhanced energetic electron precipitation, was found to intensify simultaneously with the pressure gradient enhancement before onset breakup occurs. Since the energy and energy flux of precipitating electrons reflect the upward FAC strength, these results indicate that the duskward azimuthal pressure gradient enhancement is associated with enhanced upward FAC during the late growth phase and leads to the intensification of the onset auroral arc soon before it breaks up. It is possible that this pressure gradient enhancement may lead to ballooning mode instability and thus substorm onset along the intensifying arc.Citation: Xing, X

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“…Lui (2) further reports that the "conventional" signatures of reconnection, namely southward deflections of the magnetic field (B z < 0, where B z is the Z-directed component of the magnetic field in Geocentric Solar Magnetospheric coordinates) and the increase of the convective flows in the tailward direction, were not observed until after Space Science Center, University of New Hampshire, Durham, NH 03824, USA.…”

Section: W E Used Data From Nasa's Time History Of Events and Macroscmentioning

confidence: 99%

Response to Comment on “Tail Reconnection Triggering Substorm Onset”

Angelopoulos

McFadden

Larson

et al. 2009

Science

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Lui challenges our conclusion that magnetic reconnection triggered the onset of a magnetospheric substorm. However, Lui incorrectly uses the auroral electrojet index instead of ground auroral and magnetic field pulsation signatures to determine substorm onset; single velocity and magnetic field components instead of full vectors and particle distributions to identify reconnection onset; and preliminary auroral electrojet-low index (AL) instead of ground magnometer, auroral, and magnetotail data to claim pre-existing activity. W e used data from NASA's Time History of Events and Macroscale Interactions during Substorms (THEMIS) missionto analyze the development of three magnetospheric substorms and identified reconnection as the trigger mechanism of substorm onset (1). Lui (2) challenges our conclusion for one event on several grounds, which we address here. We stand by our original interpretation of a reconnectioninitiated substorm.To argue that substorm onset took place after the onset of near-Earth current disruption, Lui equates substorm onset with an 04:54:00 UT increase in the THEMIS auroral electrojet (AE) index [see table 1 in (1)] despite the 04:51:39 UT auroral intensification, the 04:52:00 UT onset of Pi2 pulsations (irregular pulsations in the 40-to 150-s range), and the 04:52:21 UT poleward expansion of the aurora. All of these events occurred before the 04:52:27 UT onset of near-Earth activity at probe P3 and are therefore inconsistent with the current disruption model of substorms (3, 4). Although often used as a proxy, the AE index is ill suited to identifying localized onsets.Lui (2) further reports that the "conventional" signatures of reconnection, namely southward deflections of the magnetic field (B z < 0, where B z is the Z-directed component of the magnetic field in Geocentric Solar Magnetospheric coordinates) and the increase of the convective flows in the tailward direction, were not observed until after

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Comment on “Tail Reconnection Triggering Substorm Onset”

Cited by 64 publications

References 18 publications

Using ultra-low frequency waves and their characteristics to diagnose key physics of substorm onset

Using ultra-low frequency waves and their characteristics to diagnose key physics of substorm onset

Near-Earth plasma sheet azimuthal pressure gradient and associated auroral development soon before substorm onset

Response to Comment on “Tail Reconnection Triggering Substorm Onset”

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