Explosive Instabilities and Substorm Intensifications in the Earth's Magnetotail

Samson, J. C.; Dobias, Peter

doi:10.1016/b978-044451881-1/50017-4

Cited by 5 publications

(5 citation statements)

References 32 publications

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“…Dipolarization and substorm injections are commonly observed near the geosynchronous altitude for typical substorms. A substorm model that places the substorm initiation location in the near-Earth region (X GSM > À15 R E ) is the current disruption model indicated by a number of observations and considerations [e.g., Lui, 1991;Kennel, 1992;Pu et al, 1997;Erickson et al, 2000;Friedrich et al, 2001;Samson and Dobias, 2005;Donovan et al, 2008;Liang et al, 2008;Rae et al, 2009;Liu et al, 2012;Hwang et al, 2014;Murphy et al, 2014].…”

Section: Introductionmentioning

confidence: 99%

Dipolarization front and current disruption

Lui

2016

Geophysical Research Letters

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The modification of current density on the dawn‐dusk cross section of the magnetotail with the earthward approach of a dipolarization front (DF) is examined through the recently published results of a three‐dimensional (3‐D) particle‐in‐cell (PIC) simulation. It is found that the current density intensifies by ~37% abruptly within ~1.5 ion gyrotime as the DF approaches and shows localized regions with north‐south extrusions. After reaching its peak value, it undergoes a drastic current reduction (DCR) by ~65% within ~2 ion gyrotime. Breakdown of the frozen‐in condition occurs in the neutral sheet region in association with DCR, demonstrating the non‐MHD behavior of the phenomenon. The evolution of current density from this 3‐D PIC simulation bears several similarities to those observed for the current disruption (CD) phenomenon, such as explosive growth and disruption of the current density leading to a breakdown of the frozen‐in condition. The evolution is also similar to those from a previous two‐dimensional (2‐D) PIC simulation specially designed to investigate the nonlinear evolution of the cross‐field current instability for CD. One interpretation of these findings is that CD and substorm triggering can be associated with earthward intrusion of a DF into the near‐Earth plasma sheet as indicated by previous Cluster and Time History of Events and Macroscale Interactions during Substorms observations. An alternative interpretation is that both DF and CD are consequences of a global evolution from an ion‐tearing‐like instability of the magnetotail.

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Section: Introductionmentioning

confidence: 99%

Dipolarization front and current disruption

Lui

2016

Geophysical Research Letters

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“…A deepening minimum B is consistent with observations of high beta values of 50 just prior to onsets [Lui et al, 1992;Saito et al, 2008] which may importantly influence substorm onset physics. See Samson and Dobias [2005] for a high beta disruption scenario. A similar scenario emphasizing the role of the high beta on closed field lines has also been suggested for solar flares [Shibasaki, 2003].…”

Section: Introductionmentioning

confidence: 99%

Structure, force balance, and evolution of incompressible cross-tail current sheet thinning

Saito

Fairfield

et al. 2011

J. Geophys. Res.

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[1] THEMIS five-point observations on April 8, 2009 were used to study thinning of the current sheet in the near-Earth tail that led to the onset of a small substorm. Taking advantage of a fortuitous alignment of the five spacecraft near 2300 LT and 11 R E and within 1.5 R E of the current sheet center, latitudinal gradients are analyzed. A significant latitudinal pressure gradient is present indicating the necessity of a (J × B) z force to maintain the pre-onset equilibrium state. During thinning the total pressure remained approximately constant at all spacecraft rather than increasing. Within the plasma sheet, magnetic field strength increased while plasma pressure decreased due to decreasing temperature. We present a comprehensive explanation for the relationship between the thinning, the stretched structure, and development of intense current density. Our analysis of this event suggests that (1) the thinning in this event is an MHD force-balanced self-evolving process and is not a forced process due to an increased lobe field; (2) the thinning changes flux tube structure in length and curvature but not significantly in volume; (3) the thinning evolves with a change of the radial plasma pressure profile in the near-Earth tail, which is associated with a locally intensified current sheet. The conclusion is that the increased lobe field strength is not the necessary and the primary cause for cross tail current sheet thinning but rather thinning can occur within the plasma sheet as a result of unknown internal processes.

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“…We assume azimuthal symmetry for our analysis, and performed the stability analysis around 10 R E , in the region where FLRs are likely to occur [12]. This location further corresponds to a possible location of the processes responsible for forming the breakup arc [13].…”

Section: Plasma Displacement For K-h Instabilitymentioning

confidence: 99%

“…In the present work we address a nonlinear stability of the near-Earth plasma sheet during the substorm onset assuming a presence of the Kelvin-Helmholz (KH) instability. [12] outline a possible sequence of events that take place during the substorm expansion phase. This sequence assumes the initiation of the expansion phase near Earth.…”

Section: Introductionmentioning

confidence: 99%

Nonlinear stability of the near-Earth plasma sheet during substorms: 9 February 1995 event

Dobias¹,

Wanliss²,

Samson³

2006

Can. J. Phys.

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It has been previously demonstrated that several minutes prior to an onset of a magnetospheric substorm the near-Earth plasma sheet becomes unstable to resonance-type perturbations. The next logical step, examined here, is an assumption that the velocity shear in the resonance would lead to a development of a Kelvin–Helmholtz (KH) instability. Using a Grad-Shafranov equilibrium constrained by CANOPUS data, we analyze the stability properties of the near-Earth plasma sheet in the presence of a field-line resonance-generated KH instability at around 10 Earth radii. The results of the analysis are in general agreement with observations and computer modeling of substorms. As a part of the analysis, we discuss the importance of the proper distinction between the stability properties of the magnetotail, and the trigger mechanism responsible for the instability. While these two aspects of a substorm may be (and likely are) related, it is possible that they involve different types of processes that work in a complementary fashion. PACS Nos.: 06.54, 27.40, 27.72, 27.88

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Explosive Instabilities and Substorm Intensifications in the Earth's Magnetotail

Cited by 5 publications

References 32 publications

Dipolarization front and current disruption

Dipolarization front and current disruption

Structure, force balance, and evolution of incompressible cross-tail current sheet thinning

Nonlinear stability of the near-Earth plasma sheet during substorms: 9 February 1995 event

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