Substorm electron injections: Geosynchronous observations and test particle simulations

Birn, J.; Thomsen, M. F.; Borovsky, Joseph E.; Reeves, G. D.; McComas, D. J.; Belian, R. D.; Hesse, M.

doi:10.1029/97ja02635

Cited by 192 publications

(237 citation statements)

References 21 publications

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“…This is similar to the suggestion by Friedel et al (1996) and simulation result by Birn et al (1998). Although their studies did not focus on sawtooth events, our result illustrates that their results can also be applied to sawtooth-time injections.…”

Section: Spatial Extents Of the Injection Regionssupporting

confidence: 79%

“…Furthermore, the similar location of the outer limit around 10-15 R E from the Earth was well reproduced in substorm-injection simulations by Birn et al (1997bBirn et al ( , 1998. Therefore, it can be stated that the radial profile of the sawtooth-time injection is similar to non-sawtooth injections.…”

Section: Particle Signatures and Dipolarisations Observed By Themismentioning

confidence: 53%

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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: Spatial Extents Of the Injection Regionssupporting

confidence: 79%

Section: Particle Signatures and Dipolarisations Observed By Themismentioning

confidence: 53%

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

et al. 2009

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“…Early studies of the energetic electrons' pitch angle distributions during substorms included both modeling work and observational work. Modeling and observation work have shown that substorm induced electric fields accelerate electrons [Moore et al, 1981;Mauk, 1986;Aggson et al, 1983;Quinn and Southwood, 1982;Hesse, 1993, 1996;Birn et al, 1998Birn et al, , 2000.…”

Section: Introductionmentioning

confidence: 99%

Substorm associated magnetotail energetic electrons pitch angle evolutions and flow reversals: Cluster observation

Fritz

Larvaud

et al. 2006

Geophysical Research Letters

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The Cluster satellites observed a distinct pattern in the evolution of energetic electron pitch angle distributions on November 13, 2003, in the mid‐tail (radius >10RE) associated with intensifications of these electron fluxes that accompanied an observed local dipolarization of the magnetic field. The intensity of electrons (20–200 keV) were first observed to increase for perpendicular pitch angles (pancake distribution), then evolve into isotropic distributions, then further evolve into mixed distributions ‐ a combination of perpendicularly peaked distributions and beamlike distributions (cigar distribution), and at the end of each of three episodes always evolved into a beamlike or field‐aligned distribution. This evolution pattern seen at a relative fixed observing (satellite) location usually developed within the locally observed dipolarization time scale. We have interpreted this pattern to indicate that electrons were coming from different regions along the magnetotail and have gotten accelerated differently. This has led us to suggest and present a model in which Fermi acceleration dominates for electrons that are accelerated from the reconnection region, while betatron acceleration dominates for electrons that are accelerated from the mid‐tail region that is very close to the satellite location.

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“…All these studies have been performed for simple electric and magnetic field configurations, with homogeneous electric fields, the investigation of more complex threedimensional configurations has though shown that more realistic simulations are necessary to understand particle acceleration in reconnection regions [19]. Test particle simulations in three-dimensional electric and magnetic fields, obtained by magnetohydrodynamic simulations of magnetic reconnection have shown that idealized analytical two-dimensional treatments are too simplified models, which cannot give a complete understanding of the problem [20,21].…”

mentioning

confidence: 99%

Stochastic Acceleration in Turbulent Electric Fields Generated by 3D Reconnection

2006

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Electron and proton acceleration in three-dimensional electric and magnetic fields is studied through test particle simulations. The fields are obtained by a three-dimensional magnetohydrodynamic simulation of magnetic reconnection in slab geometry. The nonlinear evolution of the system is characterized by the growth of many unstable modes and the initial current sheet is fragmented with formation of small scale structures. We inject at random points inside the evolving current sheet a Maxwellian distribution of particles. In relatively short time (less than a millisecond) the particles develop a power law tail. The acceleration is extremely efficient and the electrons absorb a large percentage of the available energy in a small fraction of the characteristic time of the MHD simulation, suggesting that resistive MHD codes, used extensively in the current literature, are unable to represent the full extent of particle acceleration in 3D reconnection.It is widely accepted that magnetic reconnection plays a significant role in converting magnetic energy to thermal energy and kinetic energy of electrons and protons in laboratory plasmas, the Earth's magnetosphere, the solar corona, and in extragalactic jets [1,2].In resistive magnetohydrodynamic models, resistivity breaks the frozen-in law in a boundary layer, allowing reconnection to occur. A current sheet can be spontaneously unstable to resistive instabilities, like the tearing modes, which lead to magnetic reconnection [3,4]. Many numerical codes have been developed to study the nonlinear evolution of tearing modes in two-dimensional approximations [5]. However, three-dimensional effects may become important in modifying the spatial structure of the current sheets and the reconnection rate [6,7]. Different numerical studies have been performed to investigate collisionless magnetic reconnection using fluid models, where magnetic reconnection is made possible by electron inertia, and kinetic simulations, in two and three dimensional configurations [8,9]. It has been shown that in the three-dimensional kinetic reconnection the characteristic time scale of the instability is much faster than that of the two-dimensional tearing mode instability.The change of the topology of the magnetic field due to magnetic reconnection allows the release of magnetic energy, which can be responsible for the acceleration of particles. In two-dimensional reconnection configurations particle acceleration has been extensively studied both analytically and numerically [10,11]. The acceleration is caused by the motion of particles along the electric field in the current sheet, but the magnetic field plays a significant role since it influences the trajectory and therefore the energy gain of the particles. Recently, it has become clear that it is essential to include in the model the longitudinal component of the magnetic field, which is parallel to the electric field in the current sheet [12]- [14]. Studies of particle acceleration with a longitudinal magnetic field component have also be...

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Substorm electron injections: Geosynchronous observations and test particle simulations

Cited by 192 publications

References 21 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

Substorm associated magnetotail energetic electrons pitch angle evolutions and flow reversals: Cluster observation

Stochastic Acceleration in Turbulent Electric Fields Generated by 3D Reconnection

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