Electromagnetics of substorm onsets in the near‐geosynchronous plasma sheet

Erickson, G. M.; Maynard, N. C.; Burke, William J.; Wilson, G. R.; Heinemann, Michael

doi:10.1029/1999ja000424

Cited by 97 publications

(127 citation statements)

References 48 publications

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“…12). Erickson et al (2000) also noted similar eastward dips of the electric field ∼1-10 min prior to the initiation of the SCW formation in other CRRES data sets. Furthermore, they showed the significant earthward Poynting fluxes that appeared just after the intensification of the magnetic bays.…”

Section: Electromagnetic Field Fluctuation At Themis-csupporting

confidence: 76%

“…From this point of view, the prior activity in our event, which we call pseudobreakup, can have significant relation with the major onset, rather than the independent activity. In fact, the observed initiation of dipolarisation and shallow magnetic bays during the prior activity (from 09:04:30 UT) are similar to those after the "local onset" in Erickson et al (2000), followed by the explosive onset. Maynard et al (1996) and Erickson et al (2000) showed electric field data predominantly near the substorm onset region in the premidnight sector.…”

Section: Electromagnetic Field Fluctuation At Themis-csupporting

confidence: 57%

“…In fact, the observed initiation of dipolarisation and shallow magnetic bays during the prior activity (from 09:04:30 UT) are similar to those after the "local onset" in Erickson et al (2000), followed by the explosive onset. Maynard et al (1996) and Erickson et al (2000) showed electric field data predominantly near the substorm onset region in the premidnight sector. In fact, for isolated substorms, intense electric field disturbances are expected to be observed only near the onset region.…”

Section: Electromagnetic Field Fluctuation At Themis-csupporting

confidence: 57%

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Spatial distributions of electromagnetic field variations and injection regions during the 20 November 2007 sawtooth event

et al. 2009

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Abstract. We report multi-spacecraft and ground-based observations of a "sawtooth" event on 20 November 2007. For this event, data from three THEMIS, two GOES, and four LANL spacecraft are available as well as those from extensively distributed ground magnetometers and all-sky imagers. In the present paper we focus on the spatial extents of the electromagnetic and particle signatures of the first "tooth". In this event, auroral images and ground magnetic bays showed two activations: a pseudo onset and a major onset (we use the term pseudo onset since the former auroral brightening did not significantly expand poleward). Ground magnetic bay observations indicate that the substorm current wedge (SCW) developed after the major onset in an azimuthally wide region of ∼14-3 h MLT. Similarly, broad magnetic bay distribution was observed also for the pseudo onset prior to the major onset. Furthermore, around the pseudo onset, magnetic dipolarisations were observed from 0.5 to 5 h MLT. These observations illustrate that, during sawtooth events, activities following not only the major onset but also the pseudo onset can extend more widely than those during usual substorms. Remarkable electromagnetic field fluctuations embedded in the dipolarisation trend were seen at 0.5 and 2.5 h MLT. In particular, comprehensive plasma and field data from THEMIS showed the presence of a long-excited weak magnetosonic wave and an impulsive large-amplitude Alfvén wave with an earthward Poynting flux at around the eastward edge of the SCW; the latter was sufficiently strong for powering aurora (140 mW/m 2 Correspondence to: S. Kasahara (kshr@stp.isas.jaxa.jp) when mapped to the ionosphere). These two activations of the electromagnetic wave were identified, corresponding to the pseudo onset and the major onset. On the other hand, the dipolarisation at geosynchronous 0 h MLT was observed only after the major onset, despite its closer location to the centre of the auroral activity in terms of the MLT; this indicates that the inner radial limit of the dipolarisation region at the pseudo onset was tailward of geosynchronous altitude at 0 h MLT. The outer radial limit of the electron injection region was also found at ∼10 R E by conjunction measurements with THEMIS satellites. These radial distributions are not significantly different to those expected for usual substorms.

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Section: Electromagnetic Field Fluctuation At Themis-csupporting

confidence: 76%

Section: Electromagnetic Field Fluctuation At Themis-csupporting

confidence: 57%

Section: Electromagnetic Field Fluctuation At Themis-csupporting

confidence: 57%

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Spatial distributions of electromagnetic field variations and injection regions during the 20 November 2007 sawtooth event

et al. 2009

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“…Several instabilities have been proposed for the onset near geosynchronous orbit (e.g. Erickson et al, 2000;Lui, 1996), while an equally popular theory starts out with an instability further tailward, causing a near-Earth neutral line (Shiokawa et al, 1998). In the framework of this latter theory the pulsations could be due to a localised periodical flow braking (Kepko and Kivelson, 2001).…”

Section: Discussionmentioning

confidence: 99%

Pi2-pulsations observed in energetic electron precipitation and magnetic field in association with a substorm surge

et al. 2004

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Abstract. For a substorm 24 July 1998 PIXIE observes the onset and expansion during a perigee pass of the Polar satellite. This gives an opportunity to follow the evolution of the onset and expansion phase, almost on a global scale with relatively high temporal resolution. The substorm is presented with multiple observations throughout the magnetosphere. Following the onset of the substorm we observe a localised region of modulated energetic electron fluxes following the passage of the westward travelling surge in the pre-midnight region. We count at least six clear pulses with a period of approximately one minute. Concurrent magnetic ground measurements show similar characteristics, almost simultaneously with the pulses in precipitation. We propose several possible mechanism for the pulsations, amongst them the theory of modulated wave particle interaction first proposed by Coroniti and Kennel (1970).

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“…It is emphasized that the initial excitation of the low frequency instability occurs in a localized equatorial area of less than 1 R E in width in the near-Earth plasma sheet region [Ohtani et al, 1991]. The low frequency modes have also been observed by satellites not located at the initiation region during the substorm expansion phase [e.g., Roux et al, 1991;Erickson et al, 2000].…”

Section: Introductionmentioning

confidence: 99%

MHD Ballooning Instability in the Plasma Sheet

Cheng

Zaharia

2003

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Abstract. Based on the ideal MHD model the stability of ballooning modes is investigated by employing realistic 3D magnetospheric equilibria, in particular for the substorm growth phase. Previous MHD ballooning stability calculations making use of approximations on the plasma compressibility can give rise to erroneous conclusions. Our results show that without making approximations on the plasma compressibility the MHD ballooning modes are unstable for the entire plasma sheet where β eq ≥ 1, and the most unstable modes are located in the strong cross-tail current sheet region in the near-Earth plasma sheet, which maps to the initial brightening location of the breakup arc in the ionosphere. However, the MHD β eq threshold is too low in comparison with observations by AMPTE/CCE at X = −(8 − 9) R E , which show that a low frequency instability is excited only when β eq increases over 50. The difficulty is mitigated by considering the kinetic effects of ion gyroradii and trapped electron dynamics, which can greatly increase the stabilizing effects of field line tension and thus enhance the β eq threshold [Cheng and Lui, 1998]. The consequence is to reduce the equatorial region of the unstable ballooning modes to the strong cross-tail current sheet region where the free energy associated with the plasma pressure gradient and magnetic field curvature is maximum.

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Electromagnetics of substorm onsets in the near‐geosynchronous plasma sheet

Abstract: Abstract.A

Cited by 97 publications

References 48 publications

Spatial distributions of electromagnetic field variations and injection regions during the 20 November 2007 sawtooth event

Spatial distributions of electromagnetic field variations and injection regions during the 20 November 2007 sawtooth event

Pi2-pulsations observed in energetic electron precipitation and magnetic field in association with a substorm surge

MHD Ballooning Instability in the Plasma Sheet

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