Proton aurora and substorm intensifications

Samson, J. C.; Lyons, L. R.; Newell, P. T.; Creutzberg, F.; Xu, Bo

doi:10.1029/92gl02184

Cited by 198 publications

(215 citation statements)

References 12 publications

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“…3 or alternatively Fig. 1 of Samson et al, 1992), which is very similar to the equatorward expansion of the HF radar backscatter described in this work. Not only does it look the same but we believe it has the same underlying physical cause.…”

Section: Discussionsupporting

confidence: 82%

The electric field response to the growth phase and expansion phase onset of a small isolated substorm

et al. 1997

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Abstract. We capitalise on the very large field of view of the Halley HF radar to provide a comprehensive description of the electric field response to the substorm growth phase and expansion phase onset of a relatively simple isolated substorm ( |AL| < 250 nT) which occurred on 13 June 1988. The substorm phases are identified by their standard ground magnetic and spacecraft energetic particle signatures, which provide a framework for the radar measurements. The substorm is preceded by a prolonged period (>12 h) of magnetic quiescence, such that prior to the start of the growth phase, the apparent latitudinal motion of the radar backscatter returns is consistent with the variation in latitude of the quiet-time auroral oval with magnetic local time. The growth phase is characterised by an increasing, superimposed equatorward motion of the equatorward edge of the radar backscatter as the auroral oval expands. Within this backscatter region, there is a poleward gradient in the Doppler spectral width, which we believe to correspond to latitudinal structure in auroral emissions and magnetospheric precipitation. During the growth phase the ionospheric convection is dominated by a relatively smooth largescale flow pattern consistent with the expanding DP2 (convection) auroral electrojets. Immediately prior to substorm onset the ionospheric convection observed by the radar in the midnight sector has a predominantly equatorward flow component. At substorm onset a dramatic change occurs and a poleward flow component prevails. The timing and location are quite remarkable. The timing of the flow change is within one minute of the dispersionless injection observed at geostationary orbit and the Pi2 magnetic signature on the ground. The location shows that this sudden change in flow is due to the effect of the upward field aligned current of the substorm current wedge imposed directly within the Halley radar field of view.

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Section: Discussionsupporting

confidence: 82%

The electric field response to the growth phase and expansion phase onset of a small isolated substorm

et al. 1997

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“…It has been shown on multiple occasions that the substorm onset arc is embedded within closed field lines in the inner magnetosphere [e.g., Samson et al, 1992;Murphy et al, 2012Murphy et al, , 2014. The open-closed field line boundary is defined by the poleward edge of the electron aurora [Blanchard et al, 1995], which is significantly poleward of the substorm onset arc and conjugate to the tail reconnection site.…”

Section: Discussionmentioning

confidence: 99%

“…The open-closed field line boundary is defined by the poleward edge of the electron aurora [Blanchard et al, 1995], which is significantly poleward of the substorm onset arc and conjugate to the tail reconnection site. Auroral substorm onset occurs near the peak in the proton aurora, which is where the magnetic field topology changes from dipolar to taillike and pressure gradients develop [Samson et al, 1992]. Hence, this is also the region where the magnetotail is most unstable to, for example, shear-flow ballooning instability [Voronkov et al, 1997].…”

Section: Discussionmentioning

confidence: 99%

Statistical azimuthal structuring of the substorm onset arc: Implications for the onset mechanism

Kalmoni

Rae

Murphy

et al. 2017

Geophysical Research Letters

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The onset of an auroral substorm is generally thought to occur on a quiet, homogeneous auroral arc. We present a statistical study of independently selected substorm onset arcs and find that over 90% of the arcs studied have resolvable characteristic spatial scales in the form of auroral beads. We find that the vast majority (~88%) of auroral beads have small amplitudes relative to the background, making them invisible without quantitative analysis. This confirms that auroral beads are highly likely to be ubiquitous to all onset arcs, rather than a special case phenomena as previously thought. Moreover, as these auroral beads grow exponentially through onset, we conclude that a magnetospheric plasma instability is fundamental to substorm onset itself.

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“…We subscribe to the view that, during the growth phase of the substorm, energy is stored in the near-earth magnetotail as evidenced by the development of the weak field region in the vicinity of magnetic midnight. We accept the evidence of Samson et al (1992) that onset occurs close to the inner edge of the midnight sector plasma sheet, where region 2 current is expected to flow. We associate onset with the breakdown of the shielding electric field that has built up during the course of the growth phase (cf.…”

Section: Discussionmentioning

confidence: 99%

Creation of the substorm current wedge through the perturbation of the directly driven current system: a new model for substorm expansion

Rostoker

Friedrich

2005

Ann. Geophys.

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Abstract. The past four decades have seen a considerable amount of research on the study of magnetospheric substorms, and over most of these years the expansive phase of the substorm has been associated with the development of a three dimensional current system that has been termed the substorm current wedge. This current system has been thought to be a consequence of the short-circuiting of crosstail current through the ionosphere, and is viewed as a distinctive current system operating independently from the directly driven current with which it co-exists. The purpose of this paper is to show that the substorm current wedge should be viewed as an equivalent current system rather than a real current system. It will be shown that the magnetic perturbation pattern associated with the current wedge can be modeled as purely a perturbation of the directly driven current system in the midnight sector.

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Proton aurora and substorm intensifications

Cited by 198 publications

References 12 publications

The electric field response to the growth phase and expansion phase onset of a small isolated substorm

The electric field response to the growth phase and expansion phase onset of a small isolated substorm

Statistical azimuthal structuring of the substorm onset arc: Implications for the onset mechanism

Creation of the substorm current wedge through the perturbation of the directly driven current system: a new model for substorm expansion

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