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Journal ArticleDOI

Observational evidence for an inside-out substorm onset scenario

08 May 2009-Annales Geophysicae (Copernicus GmbH)-Vol. 27, Iss: 5, pp 2129-2140
TL;DR: In this paper, the authors present observations which provide strong support for a substorm expansion phase onset scenario in which a localized inner magnetospheric instability developed first and was later followed by the development of a Near Earth Neutral Line (NENL) farther down-tail.
Abstract: . We present observations which provide strong support for a substorm expansion phase onset scenario in which a localized inner magnetospheric instability developed first and was later followed by the development of a Near Earth Neutral Line (NENL) farther down-tail. Specifically, we find that the onset began as a localized brightening of an intensified growth phase arc which developed as a periodic series of arc-aligned (i.e. azimuthally arrayed) bright spots. As the disturbance grew, it evolved into vortical structures that propagated poleward and eventually morphed into an east-west aligned arc system at the poleward edge of the auroral substorm bulge. The evolution of the auroral intensity is consistent with an exponential growth with an e-folding time of around 188 s (corresponding to a linear growth rate, γ of 5.33×10−3 s−1). During the initial breakup, no obvious distortions of auroral forms to the north were observed. However, during the expansion phase, intensifications of the poleward boundary of the expanding bulge were observed together with the equatorward ejection of auroral streamers into the bulge. A strong particle injection was observed at geosynchronous orbit, but was delayed by several minutes relative to onset. Ground magnetometer data also shows a two phase development of mid-latitude positive H-bays, with a quasi-linear increase in H between the onset and the injection. We conclude that this event provides strong evidence in favor of the so-called "inside-out" substorm onset scenario in which the near Earth region activates first followed at a later time by the formation of a near-to-mid tail substorm X-line. The ballooning instability is discussed as a likely mechanism for the initial onset.

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Citations
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Journal ArticleDOI
TL;DR: Two mechanisms for the generation of the pre-onset current sheet are discussed, namely magnetic flux addition to the tail lobes, or other high-latitude perturbations, and magnetic flux evacuation from the near-Earth tail associated with dayside reconnection.
Abstract: Modes and manifestations of the explosive activity in the Earth’s magnetotail, as well as its onset mechanisms and key pre-onset conditions are reviewed. Two mechanisms for the generation of the pre-onset current sheet are discussed, namely magnetic flux addition to the tail lobes, or other high-latitude perturbations, and magnetic flux evacuation from the near-Earth tail associated with dayside reconnection. Reconnection onset may require stretching and thinning of the sheet down to electron scales. It may also start in thicker sheets in regions with a tailward gradient of the equatorial magnetic field $B_{z}$ ; in this case it begins as an ideal-MHD instability followed by the generation of bursty bulk flows and dipolarization fronts. Indeed, remote sensing and global MHD modeling show the formation of tail regions with increased $B_{z}$ , prone to magnetic reconnection, ballooning/interchange and flapping instabilities. While interchange instability may also develop in such thicker sheets, it may grow more slowly compared to tearing and cause secondary reconnection locally in the dawn-dusk direction. Post-onset transients include bursty flows and dipolarization fronts, micro-instabilities of lower-hybrid-drift and whistler waves, as well as damped global flux tube oscillations in the near-Earth region. They convert the stretched tail magnetic field energy into bulk plasma acceleration and collisionless heating, excitation of a broad spectrum of plasma waves, and collisional dissipation in the ionosphere. Collisionless heating involves ion reflection from fronts, Fermi, betatron as well as other, non-adiabatic, mechanisms. Ionospheric manifestations of some of these magnetotail phenomena are discussed. Explosive plasma phenomena observed in the laboratory, the solar corona and solar wind are also discussed.

96 citations

Journal ArticleDOI
TL;DR: In this paper, the authors used simultaneous ground-based, all-sky camera observations from a geomagnetically conjugate Iceland-Syowa Station pair to demonstrate that the auroral beads, whose wavelength is ∼30-50 km, evolve synchronously in the northern and southern hemispheres and have remarkable interhemispheric similarities.
Abstract: [1] Auroral beads, i.e., azimuthally arrayed bright spots resembling a pearl necklace, have recently drawn attention as a possible precursor of auroral substorms. We used simultaneous, ground-based, all-sky camera observations from a geomagnetically conjugate Iceland-Syowa Station pair to demonstrate that the auroral beads, whose wavelength is ∼30–50 km, evolve synchronously in the northern and southern hemispheres and have remarkable interhemispheric similarities. In both hemispheres: 1) they appeared almost at the same time; 2) their longitudinal wave number was similar ∼300–400, corresponding bead separation being ∼1° in longitude; 3) they started developing into a larger scale spiral form at the same time; 4) their propagation speeds and their temporal evolution were almost identical. These interhemispheric similarities provide strong evidence that there is a common driver in the magnetotail equatorial region that controls the major temporal evolution of the auroral beads; thus, the magnetosphere plays a primary role in structuring the initial brightening arc in this scale size.

82 citations


Cites background from "Observational evidence for an insid..."

  • ...…observations from the ground [Donovan et al., 2006; Liang et al., 2008; Sakaguchi et al., 2009] and from spacecraft [Elphinstone et al., 1995; Henderson, 2009] have shown that in the initial brightening arc, there exists a characteristic small-scale auroral structure, consisting of…...

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Journal ArticleDOI
TL;DR: In a global magnetohydrodynamic (MHD) simulation of the growth phase of a synthetic substorm, it is found that the self‐consistent formation and destabilization of localized magnetic field minima in the near‐Earth magnetotail are found.
Abstract: Explosive magnetotail activity has long been understood in the context of its auroral manifestations. While global models have been used to interpret and understand many magnetospheric processes, the temporal and spatial scales of some auroral forms have been inaccessible to global modeling creating a gulf between observational and theoretical studies of these phenomena. We present here an important step toward bridging this gulf using a newly developed global magnetosphere-ionosphere model with resolution capturing ≲ 30 km azimuthal scales in the auroral zone. In a global magnetohydrodynamic (MHD) simulation of the growth phase of a synthetic substorm, we find the self-consistent formation and destabilization of localized magnetic field minima in the near-Earth magnetotail. We demonstrate that this destabilization is due to ballooning-interchange instability which drives earthward entropy bubbles with embedded magnetic fronts. Finally, we show that these bubbles create localized field-aligned current structures that manifest in the ionosphere with properties matching observed auroral beads.

66 citations


Cites background from "Observational evidence for an insid..."

  • ...These dynamics result in the generation of localized perturbations in ionospheric field‐aligned currents and corresponding auroral signatures commonly referred to as beads (e.g., Henderson, 2009; Motoba et al., 2012; Nishimura et al., 2016)....

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  • ...In observations, auroral beads have also been reported both as onset arc structures (Henderson, 2009; Kalmoni et al., 2015, 2017; Nishimura et al., 2016) and not (Panov et al....

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  • ...In observations, auroral beads have also been reported both as onset arc structures (Henderson, 2009; Kalmoni et al., 2015, 2017; Nishimura et al., 2016) and not (Panov et al., 2019; Uritsky et al., 2009; Xing et al., 2020)....

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Journal ArticleDOI
12 Jun 2009-Science
TL;DR: Evidence is provided that near-Earth current disruption, occurring before the conventional tail reconnection signatures, triggered the onset of a magnetospheric substorm, and the observed auroral intensification and tail reconnections are not causally linked.
Abstract: Angelopoulos et al. (Research Articles, 15 August 2008, p. 931) reported that magnetic reconnection in Earth’s magnetotail triggered the onset of a magnetospheric substorm. We provide evidence that (i) near-Earth current disruption, occurring before the conventional tail reconnection signatures, triggered the onset; (ii) the observed auroral intensification and tail reconnection are not causally linked; and (iii) the onset they identified is a continuation of earlier substorm activities.

65 citations

Journal ArticleDOI
TL;DR: In this article, the authors used the Rice Convection Model-Equilibrium (RCM-E) and kinetic instability properties of substorm onsets to characterize the occurrence probabilities and properties of substorm auroral onset waves.
Abstract: Auroral substorms are often associated with optical ray or bead structures during initial brightening (substorm auroral onset waves). Occurrence probabilities and properties of substorm onset waves have been characterized using 112 substorm events identified in THEMIS all-sky imager data, and compared to Rice Convection Model-Equilibrium (RCM-E) and kinetic instability properties. All substorm onsets were found to be associated with optical waves, and thus optical waves are a common feature of substorm onset. Eastward-propagating wave events are more frequent than westward-propagating wave events, and tend to occur during lower-latitude substorms (stronger solar wind driving). The wave propagation directions are organized by orientation of initial brightening arcs. We also identified notable differences in wave propagation speed, wavelength (wavenumber), period and duration between westward and eastward propagating waves. In contrast, the wave growth rate does not depend on the propagation direction or substorm strength but is inversely proportional to the wave duration. This suggests that the waves evolve to poleward expansion at a certain intensity threshold, and that the wave properties do not directly relate to substorm strengths. However, waves are still important for mediating the transition between the substorm growth phase and poleward expansion. The relation to arc orientation can be explained by magnetotail structures in the RCM-E, indicating that substorm onset location relative to the pressure peak determines the wave propagation direction. The measured wave properties agree well with kinetic ballooning interchange instability, while cross-field current instability and electromagnetic ion cyclotron instability give much larger propagation speed and smaller wave period.

64 citations


Cites background from "Observational evidence for an insid..."

  • ...Such ray structures are also called beads and can be characterized as an optical wave-like structure along an initial brightening arc [Donovan et al., 2006; Henderson, 2009; Rae et al., 2010] (hereinafter called substorm auroral onset waves or onset waves for convenience)....

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References
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Journal ArticleDOI
TL;DR: Magnetospheric substorms model modification for growth phase inclusion prior to explosive expansion phase was proposed in this article for the growth phase and the expansion phase, respectively, and the model was modified for the exponential expansion phase.
Abstract: Magnetospheric substorms model modification for growth phase inclusion prior to explosive expansion phase

464 citations


"Observational evidence for an insid..." refers background in this paper

  • ...Note that this phase of the substorm was not originally described byAkasofu(1964) but was added later by McPherron(1970)....

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Journal ArticleDOI
TL;DR: In this article, a detailed analysis of an isolated dispersionless substorm is performed on the basis of field and particle data collected in situ by the geostationary satellite GEOS 2 and of data from ground-based instruments installed close to the GEOS2 magnetic footprint.
Abstract: The detailed analysis of an isolated dispersionless substorm is performed on the basis of field and particle data collected in situ by the geostationary satellite GEOS 2 and of data from ground-based instruments installed close to the GEOS 2 magnetic footprint. These data give evidence for (1) quasi-periodic variations of the magnetic field configuration, which is alternatively taillike and dipolelike, (2) in-phase oscillations of the flux of energetic electrons, which is high when the configuration is dipolelike and vice versa, (3) a gradient in the flux of energetic ions, which is, on the average, earthward but undergoes large fluctuations around this average direction, and (4) large transient fluctuations of the quasi-dc electric field, which reverses its direction from eastward to westward. It is shown that these results are consistent with the development of an instability which leads to a westward propagating “wave”. The source of the instability is the differential drift of energetic electrons and ions in a highly stressed magnetic field configuration (in a high β plasma). Evidence is given for a system of localized field-aligned currents flowing alternately earthward and equatorward at the leading and trailing edges of the westward propagating wave. This current system resulting from the temporal development of the instability produces the so-called Pi 2 pulsations, at the ionospheric level. The closure of this current system in the equatorial region leads to a current antiparallel to the tail current, and therefore to its reduction or cancellation. This reduction/cancellation of the tail current restores the dipole magnetic field (dipolarization) and generates a large westward directed induced electric field (injection). Hence, dipolarization and injection are the consequences of the instability. Finally, it is suggested that the westward traveling surge observed simultaneously by all-sky cameras, close to the magnetic field of GEOS 2, is the image of the instability in the equatorial region transmitted to the upper atmosphere by precipitating electrons.

397 citations


"Observational evidence for an insid..." refers background in this paper

  • ...…1977; Lui, 1978; Lui et al., 1988; Roux, 1985; Smith et al., 1986; Rostoker and Eastman, 1987; Kan et al., 1988; Goertz and Smith, 1989; Lui, 1991; Roux et al., 1991; Kan, 1993; Hones and McPherron, 1994; Lyons, 1995; Miura, 2001; Zhu et al., 2007), and while some of these models have been…...

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  • ...A hypothetical development of the ballooning instability in the inner magnetosphere is shown schematically in Fig.9 (after Roux et al., 1991)....

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Book
01 Jan 1977
TL;DR: In this article, magnetospheric substorm physics are updated in the monograph and the open magnetosphere and the auroral oval are discussed, including open field lines, field-aligned currents, auroral particles and atmospheric emissions, plasma mantle, plasma sheet, radiation belts, magnetic flux transfer to the magnetotail, polar cap phenomena, substorm parameters and instabilities.
Abstract: Magnetosphere substorm physics are updated in the monograph. Major topics include: (1) open magnetosphere and the auroral oval; (2) auroras and auroral particles; (3) plasma distribution in the magnetosphere; (4) magnetosphere responses to interplanetary disturbances; (5) magnetospheric substorms and magnetotail phenomena; (6) magnetospheric currents, plasma injection, plasmasphere disturbances; and (7) magnetospheric substorms and solar-terrestrial relations. Other topics covered include: open field lines and the open magnetosphere, field-aligned currents, auroral particles and atmospheric emissions, plasma mantle, plasma sheet, radiation belts, magnetic flux transfer to the magnetotail, polar cap phenomena, substorm parameters, thinning of the plasma sheet, auroral electrojets, diurnal variations and dawn-dusk asymmetry of particle distributions, and instabilities.

366 citations


"Observational evidence for an insid..." refers background in this paper

  • ...…well equatorward of the open-closed boundary on or near the most equatorward discrete arc and that this activity maps fairly close to the Earth (Akasofu, 1977; Kaufmann, 1987; Samson et al., 1992; Murphree et al., 1993; Henderson, 1994; Samson, 1994), and (2) That reconnection and plasmoid…...

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  • ...Two key observational constraints that have guided the development of substorm models to date are: (1) That auroral onset (or “auroral breakup”) occurs well equatorward of the open-closed boundary on or near the most equatorward discrete arc and that this activity maps fairly close to the Earth (Akasofu, 1977; Kaufmann, 1987; Samson et al. , 1992; Murphree et al. , 1993; Henderson , 1994; Samson, 1994), and (2) That reconnection and plasmoid releases are typically associated with substorms and that this activity maps...

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Journal ArticleDOI
TL;DR: In this article, the authors construct a coherent description of substorm development by extracting some important components from these existing models, including the ionospheric influence on substorm expansion onset, current disruptions leading to convection surges and tailward propagating rarefaction waves, wave-induced precipitation, local time expansion of the disturbance region via velocity-shear-related instabilities, plasma sheet heating by resonant absorption of hydromagnetic waves, and the formation of magnetic reconnection domains.
Abstract: Three decades of research in magnetospheric substorms has not led to a general consensus view of the substorm process. Several substorm models, mostly phenomenological, are presently under consideration. These competing models, each being justifiable on the basis of certain features of a substorm, have major differences as well as similarities among them. A synthesis substorm model is desirable, as first suggested by Siscoe (1986). In this paper we construct a coherent description of substorm development by extracting some important components from these existing models. The scenario of the synthesis model includes the ionospheric influence on substorm expansion onset, current disruptions leading to convection surges and tailward propagating rarefaction waves, wave-induced precipitation, local time expansion of the disturbance region via velocity-shear-related instabilities, plasma sheet heating by resonant absorption of hydromagnetic waves, and the formation of magnetic reconnection domains. This synthesis represents one possible way to integrate the different existing models coherently.

361 citations


"Observational evidence for an insid..." refers background in this paper

  • ...…Hones, 1977; Lui, 1978; Lui et al., 1988; Roux, 1985; Smith et al., 1986; Rostoker and Eastman, 1987; Kan et al., 1988; Goertz and Smith, 1989; Lui, 1991; Roux et al., 1991; Kan, 1993; Hones and McPherron, 1994; Lyons, 1995; Miura, 2001; Zhu et al., 2007), and while some of these models have…...

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  • ...Lui (1991) proposed a “Synthesis Model” in which the onset first initiates in the near-Earth region due to the growth of an instability there....

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  • ...Numerous models or mechanisms have been introduced over the past 40 years in attempts to explain the observed phenomenology (e.g.Swift, 1967; Hones et al. , 1973; Russell and McPherron , 1973; McPherron et al. , 1973; Hones, 1977; Lui, 1978; Lui et al., 1988; Roux, 1985; Smith et al. , 1986; Rostoker and Eastman, 1987; Kan et al. , 1988; Goertz and Smith , 1989; Lui, 1991; Roux et al. , 1991; Kan, 1993; Hones and McPherron, 1994; Lyons, 1995; Miura, 2001; Zhu et al. , 2007), and while some of these models have been rejected or abandoned over the years, others have been continuously modified and updated....

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Journal ArticleDOI
TL;DR: In this article, the authors present multi-instrument observations from the ISEE1 and ISEE 2 spacecraft to argue that when the plasma sheet becomes thick and close to its equilibrium state, the plasma and magnetic field signatures of high-speed flow events are consistent with the theoretically predicted signatures of plasma-depleted flux tubes or "bubbles".
Abstract: Recent studies have shown that most Earthward transport hi the midtail, high-beta plasma sheet takes place in the form of short-lived, high-speed plasma flow bursts. Bursty bulk flows are observed both when the plasma sheet is thin, such as during substorm expansion, and when it is thick, such as during substorm recovery. We present multi-instrument observations from the ISEE1 and ISEE 2 spacecraft to argue that when the plasma sheet becomes thick and close to its equilibrium state, the plasma and magnetic field signatures of high-speed flow events are consistent with the theoretically predicted signatures of plasma-depleted flux tubes or “bubbles” [Pontius and Wolf, 1990; Chen and Wolf, 1993]. These signatures consist of a decrease in the plasma pressure and an increase in the Bz-component of the magnetic field accompanying the high speed flow. We show that the Earthward moving bubbles are separated from the plasma ahead of them by a sharp tangential discontinuity. The layer ahead of the bubbles exhibits flow and magnetic field shear consistent with flow around an Earthward moving obstacle. The bubble is in approximate total pressure balance with the surrounding medium. We show that there is a systematic difference in the orientation of the discontinuity measured at ISEE 1 and 2, implying a small (about 1–3 RE) cross-tail size of the bubbles.

340 citations


"Observational evidence for an insid..." refers background in this paper

  • ...…or “bubbles” that rapidly propagate Earthward and produce streamers as an ionospheric signature (e.g. seeCh n and Wolf, 1993; Nakamura et al., 1993; Henderson, 1994; Henderson et al., 1994; Henderson et al., 1998; Lyons et al., 1999; Sergeev et al., 1996; Zesta et al., 2000; Nakamura et al., 2005)....

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