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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: In this paper, ground-based measurements from the CANOPUS array of meridian scanning photometers and precipitating ion and electron data from the DMSP F9 satellite show that the electron arc which brightens to initiate substorm intensifications is formed within a region of intense proton precipitation that is well equatorward (approximately four to six degrees) of the nightside open-closed field line boundary.
Abstract: Ground based measurements from the CANOPUS array of meridian scanning photometers and precipitating ion and electron data from the DMSP F9 satellite show that the electron arc which brightens to initiate substorm intensifications is formed within a region of intense proton precipitation that is well equatorward (approximately four to six degrees) of the nightside open-closed field line boundary. The precipitating protons are from a population that is energized via earthward convection from the magnetotail into the dipolar region of the magnetosphere and may play an important role in the formation of the electron arcs leading to substorm intensifications on dipole-like field lines.

220 citations


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

  • ...…that (1) the breakup likely maps close to the Earth near the region separating dipole-like field lines from more stretched tail-like field lines (Samson et al., 1992), (2) the breakup disturbance developed as an azimuthally arrayed series of bright spots that distorted poleward as they grew,…...

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  • ...…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…...

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Journal ArticleDOI
TL;DR: In this paper, the authors present observations from the Viking UV imager, and the Los Alamos National Laboratory geosynchronous energetic particle detectors that strongly suggest that the north-south aligned structures formed impulsively and repetitively during the expansion phase of substorms may be an ionospheric manifestation of BBFs.
Abstract: Bursty Bulk Flow (BBF) events are an important means of plasma transport in the Earth's magnetotail during substorms. While several studies have been performed using in-situ plasma and field data to determine the characteristics of BBFs, remarkably little attention has been paid to the question of whether or not these events also manifest themselves in the auroral ionosphere. In this paper, we present observations from the Viking UV imager, and the Los Alamos National Laboratory geosynchronous energetic particle detectors that strongly suggest that the north-south aligned structures formed impulsively and repetitively during the expansion phase of substorms may be an ionospheric manifestation of BBFs.

201 citations


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

  • ...see Hones, 1977) violated the first constraint (onset was not as close to the Earth as required); early versions of the Current Disruption (CD) model (e.g. seeLui, 1978, andLui et al., 1988) and the MIcoupling model ofKan et al.(1988) largely disregarded the second constraint (onset was near-Earth, but X-lines did not play an integral role); the Thermal Catastrophe (TC) model (Smith et al....

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  • ...…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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Journal ArticleDOI
TL;DR: In this paper, the expansion phase of substorms results from a reduction in the large-scale electric field imparted to the magnetosphere from the solar wind, following a ≳ 30-min growth phase due to an enhancement in this electric field.
Abstract: It is proposed here that the expansion phase of substorms results from a reduction in the large-scale electric field imparted to the magnetosphere from the solar wind, following a ≳ 30-min growth phase due to an enhancement in this electric field. The reduction in the electric field is assumed to propagate antisunward within the magnetosphere. Triggering by a reduction in the electric field is suggested by the observation that substorms are often triggered by northward turnings of the interplanetary magnetic field (IMF). However, under the theory presented here, substorms may be triggered by anything that causes an electric field reduction such as a reduction in the magnitude of the y component of the IMF. A reduction in the large-scale electric field disrupts both the inward motion and energization of plasma sheet particles that occurs during the growth phase. It is suggested here that this can lead to formation of the expansion phase current wedge and active aurora. The current wedge results from the magnetic drift of ions, which has a speed proportional to particle energy, and a large azimuthal gradient in mean particle energy that is expected to develop in the vicinity of magnetic midnight during the growth phase. Current wedge formation will most likely be initiated near the radial distance (∼6-10 RE) of the peak in the growth phase plasma pressure distribution, and then propagate tailward from that region. Order-of-magnitude calculations show that the above proposal can account for the rapid development of the expansion phase relative to the growth phase, the magnitude of the reduction in the cross-tail current within the current wedge, the speeds of tailward and westward expansion of the current reduction region, the speeds of poleward and westward motion of active aurora in the ionosphere, and the magnitude of wedge field-aligned currents that connect the ionospheric region of active auroral to the divergent cross-tail current within the magnetosphere.

196 citations

Journal ArticleDOI
TL;DR: In this article, a study of the substorm-related variations of the magnetotail plasma sheet is presented, which is causally related to a rapid poleward shift or "leap" of the principal current of the auroral electrojet evidenced by recovery of magnetic bays at auroral latitudes.
Abstract: We report a study of the substorm-related variations of the magnetotail plasma sheet. The study uses data, much of it previously published, obtained by Vela and Imp satellites in the range −6 RE > XSM > −60 RE, where XSM is geocentric distance measured along the solar magnetospheric x axis. Evidence is presented that the thickening or recovery of the plasma sheet, which has been shown in Vela satellite measurements (at γ ≈ 18 RE) to occur late in substorms, is causally related to a rapid poleward shift or ‘leap’ of the principal current of the auroral electrojet evidenced by recovery of magnetic bays at auroral latitudes (65° ≲ λm ≲ 70°) and their onset at low polar cap latitudes (e.g., λm ≈ 74°). That is, it appears to be inaccurate to regard the thickening of the plasma sheet in the far magnetotail as a process that commences near the earth at the onset of the expansive phase of a substorm and moves more or less uniformly out into the tail as the expansive phase of the substorm evolves. A schematic description of the responses of the plasma sheet to a substorm, based on this study and previous studies, is presented.

177 citations


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

  • ...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…...

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Journal ArticleDOI
TL;DR: In this article, the authors present direct evidence that transient Earthward flow bursts in the magnetotail can produce an observable signature in the optical aurora, which is a north-south aligned auroral structures that are extensions of transient intensifications near the poleward boundary of the auroral oval.
Abstract: We present direct evidence that transient Earthward flow bursts in the magnetotail can produce an observable signature in the optical aurora. This signature is north-south aligned auroral structures that are extensions of transient intensifications near the poleward boundary of the auroral oval. Our study focuses on the period from 0500 to 0700 UT on January 7, 1997, during which five distinct flow bursts are observed in the Geotail data. At that time, the spacecraft was located approximately 30 RE downtail on field lines that project down to the CANOPUS array of ground based instruments. We find that each of the flow bursts seen in the Geotail data is associated with an auroral poleward boundary intensification (PBI) observed in the CANOPUS meridian scanning photometer (MSP) data, which appears as a north-south aligned auroral structure in the CANOPUS all-sky imager (ASI) data. Based on these observations we estimate that the fast flows originated between 50 and 100 RE downtail.

161 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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