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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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15 citations


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

  • ...These are often observed to propagate along the onset arc as they form and evolve and also observed to expand and/or move polewards [e.g., Henderson, 2009; Kalmoni et al., 2015]....

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  • ...…to onset (see Figure 2c) in a way are similar in appearance to auroral beads, also referred to as azimuthal auroral forms or spatially periodic auroral spots, reported in the literature [e.g., Elphinstone et al., 1995; Liang et al., 2008; Henderson, 2009; Rae et al., 2009; Kalmoni et al., 2015]....

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Journal ArticleDOI
TL;DR: In this paper, the authors present synoptic observations of the 21 December 2006 substorm event by the THEMIS ground-based All-Sky-Imagers, the ISUAL CCD Imager aboard the FORMOSAT-2 satellite, the geosynchronous satellites and the groundbased magnetometers, and discuss the implication of the observations.
Abstract: . We present synoptic observations of the 21 December 2006 substorm event by the THEMIS ground-based All-Sky-Imagers, the ISUAL CCD Imager aboard the FORMOSAT-2 satellite, the geosynchronous satellites and the ground-based magnetometers, and discuss the implication of the observations. There are three subsequent arc breakups with time separation of

15 citations

Journal ArticleDOI
TL;DR: The Cassini/UVIS, MAG and RPWS data used in this study will be soon available through the Planetary Data System (https://pds.nasa.gov).
Abstract: The Cassini/UVIS, MAG and RPWS data used in this study will be soon available through the Planetary Data System (https://pds.nasa.gov).

14 citations


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

  • ...Birn et al. (2004) and Henderson (2009) suggested that these earthward flows are associated with dipolarized field lines and magnetotail reconnection....

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References
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Journal ArticleDOI
TL;DR: In this paper, a working model of simultaneous auroral activity over the entire polar region is presented in terms of the auroral substorm, which has two characteristic phases, an expansive phase and a recovery phase.

1,460 citations

Journal ArticleDOI
TL;DR: In this paper, the authors present a phenomenological model of the magnetospheric substorm sequence, which can be divided into three main phases: the growth phase, the expansion phase, and the recovery phase.
Abstract: In the eight preceding papers, two magnetospheric substorms on August 15, 1968, were studied with data derived from many sources. In this, the concluding paper, we attempt a synthesis of these observations, presenting a phenomenological model of the magnetospheric substorm. On the basis of our results for August 15, together with previous reports, we believe that the substorm sequence can be divided into three main phases: the growth phase, the expansion phase, and the recovery phase. Observations for each of the first three substorms on this day are organized according to this scheme. We present these observations as three distinct chronologies, which we then summarize as a phenomenological model. This model is consistent with most of our observations on August 15, as well as with most previous reports. In our interpretation we expand our phenomenological model, briefly described in several preceding papers. This model follows closely the theoretical ideas presented more quantitatively in recent papers by Coroniti and Kennel (1972a, b; 1973). A southward turning of the interplanetary magnetic field is accompanied by erosion of the dayside magnetosphere, flux transport to the geomagnetic tail, and thinning and inward motion of the plasma sheet. Our observations indicate, furthermore, that the expansionmore » phase of substorms can originate near the inner edge of thc plasm sheet as a consequence of rapid plasma sheet thinnig. At this time a portion of the inner edge of the tail current is short circuited' through the ionosphere. This process is consistent with the formation of a neutral point in the near-tail region and its subsequent propagation tailward. However, the onset of the expansion phase of substorms is found to be far from a simple process. Expansion phases can be centered at local times far from midnight, can apparently be localized to one meridian, and can have multiple onsets centered at different local times. Such behavior indicates that, in comparing observations occurring in different substorms, careful note should be made of the localization and central meridian of cach substorm. (auth)« less

1,138 citations

Journal Article
TL;DR: In this article, observations made during three substorms on August 15, 1968, are shown to be consistent with current theoretical ideas about the cause of substorm, and the phenomenological model described in several preceding papers is further expanded.
Abstract: Observations made during three substorms on August 15, 1968, are shown to be consistent with current theoretical ideas about the cause of substorms. The phenomenological model described in several preceding papers is further expanded. This model follows closely the theoretical ideas presented more quantitatively in recent papers by Coronti and Kennel (1972 and 1973).

951 citations

Journal ArticleDOI
TL;DR: In this article, a phenomenological or qualitative model of the substorm sequence is presented, where the flux transport is driven by the merging of the magnetospheric and interplanetary magnetic fields.
Abstract: The tail plays a very active and important role in substorms. Magmetic flux eroded from the dayside magnetosphere is stored here. As more and more flux is transported to the magnetotail and stored, the boundary flares more, the field strength in the tail increases, and the currents strengthen and move closer to the earth. Further, the plasma sheet thins and the magnetic flux crossing the neutral sheet lessens. The experimental evidence for these processes is discussed and a phenomenological or qualitative model of the substorm sequence is presented. In this model, the flux transport is driven by the merging of the magnetospheric and interplanetary magnetic fields. During the growth phase of substorms the merging rate on the dayside magnetosphere exceeds the reconnection rate in the neutral sheet.

552 citations


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

  • ...…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,…...

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Journal ArticleDOI
TL;DR: In this paper, the authors studied possible braking mechanisms of high-speed ion flows in the near Earth central plasma sheet for radial distances between 9 and 19 Earth Radii (RE) on the basis of observations made by the AMPTE/IRM satellite.
Abstract: We have studied possible braking mechanisms of high-speed ion flows in the near-Earth central plasma sheet for radial distances between 9 and 19 Earth Radii (RE) on the basis of observations made by the AMPTE/IRM satellite. Flows with velocities in excess of 400 km/s are almost always Earthward for this range, indicating that the source of the flows is beyond 19 RE. Though the occurrence rate of the high-speed flows substantially decreases when the satellite comes closer to the Earth, high-speed flows with velocities higher than 600 km/s are still observed. We suggest that the high-speed flows are stopped at a clear boundary between the regions of dipolar field and tail-like field in the plasma sheet. The boundary corresponds to the inner edge of the neutral sheet. The average jump of the magnetic field at the boundary, which is estimated from the observations by assuming a pressure balance, is 6.7 nT. The inertia current caused by the braking of the flow and the current caused by pileup of the magnetic flux at the stopping point are quantitatively estimated and discussed in relation to the formation of the substorm current wedge.

480 citations


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

  • ...The deceleration or “braking” of these flow bursts in the near-Earth region produces the familiar current wedge, Pi2 pulsations and breakup activity on or near the most equatorward arc (Haerendel, 1992; Shiokawa et al., 1997, 1998)....

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