A cross‐field current instability for substorm expansions

Lui, A. T. Y.; Chang, Chein‐Chi; Mankofsky, A.; Wong, H. K.; Winske, D.

doi:10.1029/91ja00892

Cited by 245 publications

(245 citation statements)

References 59 publications

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“…These events are referred to as current disruption, and a current-driven instability, known as the crossfield current instability (CCI), has been proposed to account for the observed current disruption features. Linear and quasi-linear calculations of CCI have yielded instability characteristics consistent with observed current disruption and substorm onset characteristics [Lui et al, 1991Yoon and Lui, 1993]. However, the CCI theory has not addressed at length how the instability onset location is tied to field lines threading an auroral arc except for noting that CCI occurs in regions where ions are unmagnetized, which in turn corresponds to a region of isotropic ion precipitation in the ionosphere.…”

Section: Introductionmentioning

confidence: 98%

A substorm model with onset location tied to an auroral arc

Lui¹,

Murphree²

1998

Geophysical Research Letters

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Abstract.Two important observational constraints on substorm onset theories are that (1) substorm onset occurs on field lines of a pre-existing auroral arc, and (2) reduction of the cross-tail current occurs in the near-Earth magnetotail. Recent progress in linking generation of at least some auroral arcs to field line resonances (FLRs) and current disruption to possibly the cross-field current instability (CCI) suggests a synergistic combination of these two theories. We suggest that as the cross-tail current sheet thins to the extent that ions become unmagnetized at the end of substorm growth phase, the equatorial electric field associated with FLRs can amplify significantly the cross-tail current to exceed the instability threshold. This combined theory naturally accounts for the observational constraints of substorm onset starting on a pre-existing auroral arc and linking closely with current reduction in the near-Earth magnetotail. It is compatible with the observation of the most equatorward auroral arc being the most likely one for initial brightening because the cross-tail current is most intense in its near-Earth end and is therefore most likely to exceed the unstable threshold for CCI. It is also consistent with auroral precipitation fading to be a common feature before an auroral breakup.Other predictions yet to be tested are that (1) the onset is more favorable for the phase of the resonance in which the resonance-associated field-aligned current is directed from the ionosphere to the magnetosphere, and (2) the onset is more favorable poleward of the resonance shell or auroral arc.

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Section: Introductionmentioning

confidence: 98%

A substorm model with onset location tied to an auroral arc

Lui¹,

Murphree²

1998

Geophysical Research Letters

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“…Their analysis assumed unmagnetized ions, so that an ion trajectory was treated as a straight line. One of the first applications of this instability was in the study of current disruption during substorm expansions in the geomagnetic tail (Lui et al 1991). Wu et al (1992) subsequently studied the instability more generally, and found that, even when relaxing the condition of unmagnetized ions and small β i , the zero-frequency instability persists, and in contrast to other cross-field drift instabilities (such as the modified two-stream instability), the growth rate remains high even for high β i .…”

Section: Appendix a Ion Weibel Instabilitymentioning

confidence: 99%

Microstructure in two- and three-dimensional hybrid simulations of perpendicular collisionless shocks

et al. 2016

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Supercritical collisionless perpendicular shocks have an average macrostructure determined primarily by the dynamics of ions specularly reflected at the magnetic ramp. Within the overall macrostructure, instabilities, both linear and nonlinear, generate fluctuations and microstructure. To identify the sources of such microstructure, high-resolution two-and three-dimensional simulations have been carried out using the hybrid method, wherein the ions are treated as particles and the electron response is modelled as a massless fluid. We confirm the results of earlier two-dimensional (2-D) simulations showing both field-parallel aligned propagating fluctuations and fluctuations carried by the reflected-gyrating ions. In addition, it is shown that, for 2-D simulations of the shock coplanarity plane, the presence of short-wavelength fluctuations in all magnetic components is associated with the ion Weibel instability driven at the upstream edge of the foot by the reflected-gyrating ions. In 3-D simulations we show for the first time that the dominant microstructure is due to a coupling between field-parallel propagating fluctuations in the ramp and the motion of the reflected ions. This results in a pattern of fluctuations counter-propagating across the surface of the shock at an angle inclined to the magnetic field direction, due to a combination of field-parallel motion at the Alfvén speed of the ramp and motion in the sense of gyration of the reflected ions.

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“…From this viewpoint, the diffusion is due to anomalous resistivity that waxes and wanes in response to the excitation and quenching of a current-driven instability; one that is excited when the current density gets above a critical level [Papadopoulos, 1985;Lui et al, 1991Lui et al, , 1993Yoon and Lui, 1996] and is quenched when the current density is driven below a level that is lower than the critical one.…”

Section: Lu Modelmentioning

confidence: 99%

Self‐organized criticality in the substorm phenomenon and its relation to localized reconnection in the magnetospheric plasma sheet

Klimas¹,

Valdivia²,

Vassiliadis³

et al. 2000

J. Geophys. Res.

144

106

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Abstract. Evidence is presented that suggests that there is a significant self-organized criticality (SOC) component in the dynamics of substorms in the magnetosphere. We assume that observations ofbursty bulk flows, fast flows, localized dipolarizations, plasma turbulence, etc. show that multiple localized reconnection sites provide the basic avalanche phenomenon in the establishment of SOC in the plasma sheet. First results are presented from a study of this avalanche process based on this working assumption. A magnetic field reversal model is discussed. Resistivity, in this model, is self-consistently generated in response to the excitation of an idealized currentdriven instability. When forced by convection of magnetic flux into the field reversal region, the model yields rapid magnetic field annihilation through a dynamic behavior that is shown to exhibit many of the characteristics of SOC. Over a large range of forcing strengths, the annihilation rate is shown to self-adjust to balance the rate at which flux is convected into the reversal region. Several analogies to magnetotail dynamics are discussed: (1) It is shown that the presence of a localized criticality in the model produces a remarkable stability in the global configuration of the field reversal while simultaneously exciting extraordinarily dynamic internal evolution. (2) Under steady forcing it is shown that a loading-unloading cycle may arise that, as a consequence of the global stability, is quasi-periodic and, therefore, predictable despite the presence of internal turbulence in the field distribution. Indeed, it is shown that the global loading-unloading cycle is a consequence of the internal turbulence. (3) It is shown that under steady, strong forcing the loading-unloading cycle vanishes. Instead, a recovery from a single unloading persists indefinitely. The field reversal is globally very steady while internally it is very dynamic as field annihilation goes on at the rate necessary to match the strong forcing. From this result we speculate that steady magnetospheric convection events result when the plasma sheet has been driven close to criticality over an extended spatial domain. During these events we would expect to find localized reconnection sites distributed over the spatial domain of near criticality, and we would expect to find plasma sheet transport in that domain to be closely related to that of BBF and fast flow events.

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A cross‐field current instability for substorm expansions

Cited by 245 publications

References 59 publications

A substorm model with onset location tied to an auroral arc

A substorm model with onset location tied to an auroral arc

Microstructure in two- and three-dimensional hybrid simulations of perpendicular collisionless shocks

Self‐organized criticality in the substorm phenomenon and its relation to localized reconnection in the magnetospheric plasma sheet

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