Substorm dynamics revealed by ground observations of two-dimensional auroral structures on 9 October 2000

Liang, J.; Donovan, E.; Sofko, G. J.; Trondsen, T.

doi:10.5194/angeo-23-3599-2005

Cited by 8 publications

(12 citation statements)

References 29 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The onset arc brightens and develops a ray structure or beads with apparent eastward motion. Sudden appearance of such eastward motions has been reported by Dubyagin et al [2003], Liang et al [2005], Rae et al [2009], and Shiokawa et al [2009]. The structures soon grow into brighter and coarser poleward protrusions and finally break into complex, mostly west eastward oriented curtains under rapidly increasing brightness.…”

Section: Current Sheet Avalanchementioning

confidence: 80%

Substorm onset: Current sheet avalanche and stop layer

Haerendel

2015

JGR Space Physics

View full text Add to dashboard Cite

A new scenario is presented for the onset of a substorm and the nature of the breakup arc.There are two main components, current sheet avalanche and stop layer. The first refers to an earthward flow of plasma and magnetic flux from the central current sheet of the tail, triggered spontaneously or by some unknown interaction with an auroral streamer or a suddenly appearing eastward flow at the end of the growth phase. The second offers a mechanism to stop the flow abruptly at the interface between magnetosphere and tail and extract momentum and energy to be partially processed locally and partially transmitted as Poynting flux toward the ionosphere. The stop layer has a width of the order of the ion inertial length. The different dynamics of the ions entering freely and the magnetized electrons create an electric polarization field which stops the ion flow and drives a Hall current by which flow momentum is transferred to the magnetic field. A simple formalism is used to describe the operation of the process and to enable quantitative conclusions. An important conclusion is that by necessity the stop layer is also highly structured in longitude. This offers a natural explanation for the coarse ray structure of the breakup arc as manifestation of elementary paths of energy and momentum transport. The currents aligned with the rays are balanced between upward and downward directions. While the avalanche is invoked for explaining the spontaneous substorm onset at the inner edge of the tail, the expansion of the breakup arc for many minutes is taken as evidence for a continued formation of new stop layers by arrival of flow bursts from the near-Earth neutral line. This is in line with earlier conclusions about the nature of the breakup arc. Small-scale structure, propagation speed, and energy flux are quantitatively consistent with observations. However, the balanced small-scale currents cannot constitute the substorm current wedge. The source of the latter must be located just earthward of the stop layer in the near-dipolar magnetosphere and be powered by the internal energy of the flow bursts. The stop layer mechanism is in some way the inverse of reconnection, as it converts flow into electromagnetic energy, and may have wide applicability in astrophysical plasmas.

show abstract

Section: Current Sheet Avalanchementioning

confidence: 80%

Substorm onset: Current sheet avalanche and stop layer

Haerendel

2015

JGR Space Physics

View full text Add to dashboard Cite

show abstract

“…While we cannot completely exclude the possibility of a ''propagational'' scenario from a point source, a careful examination of the image series makes us more disposed to the view that the initial breakup actually occurs simultaneously over an azimuthally extended segment of the current sheet that is preconditioned (possibly via ballooning mode) and subject to sudden disruptions. The instability growth rate is spatially dependent, such that the brightening of discrete ''spots'' or fragments may exhibit an apparent time-lapsed emergence (thus a ''propagational'' illusion) due to the threshold effect discussed by Liang et al [2005] (see their Figure 13).…”

Section: Discussionmentioning

confidence: 99%

Intensification of preexisting auroral arc at substorm expansion phase onset: Wave‐like disruption during the first tens of seconds

Liang¹,

Donovan²,

Liu³

et al. 2008

Geophysical Research Letters

Self Cite

131

166

View full text Add to dashboard Cite

With the deployment of the all‐sky imager array of the THEMIS mission, we were able to construct a preliminary database of auroral substorm expansion phase onsets, from which we have established a number of common features characterizing the first tens of seconds of the substorm auroral intensification. We find that the intensification occurs within ∼10 sec over an arc segment extending approximately 1 h MLT and featuring wave‐like formations distributed in longitude. The longitudinal wave number ranges between 100 and 300 such that the wavelength is comparable to the ion gyroradius in the central plasma sheet. The scale the intensification is about 10–30 sec. This study casts important observational constraints on substorm onset theories.

show abstract

“…One complication that is of special importance to this paper lies in the possibility that the substorm expansion may not proceed continuously but rather take place as a series of consecutive and discrete activations, particularly around the onset time. The auroral imager observations frequently reveal that substorm auroral activation evolves in an azimuthally discrete manner, exhibiting wave‐like disturbances [ Elphinstone et al , 1995; Liang et al , 2005]. Their propagation can be either eastward or westward, with azimuthal wave number ranging from a few tens to above one hundred.…”

Section: Model Runs For Different Azimuthal Locations Of Scwmentioning

confidence: 99%

Azimuthal structures of substorm electron injection and their signatures in riometer observations

et al. 2007

Self Cite

View full text Add to dashboard Cite

[1] We propose a theoretical model to investigate the effects of the curvature/gradient (c/g) drift and the finite azimuthal extent of the dipolarization region on the electron injection process associated with the substorm dipolarization. We study the azimuthal structure of high-energy (>30 keV) electron precipitation flux and compare the result with riometer observations. We are able to reproduce three basic archetypes of riometer responses to substorms, namely, the spike, dispersionless injection, and dispersed injection events catalogued in previous observations. The electron injection near the duskward edge of the dipolarization region is most subject to azimuthal c/g drift loss, appearing in riometer observations as the ''spike'' feature. The ''dispersionless injection'' response is seen inside the dipolarization region but some distance away from its western border: or, alternatively, when the substorm has a rapid westward expansion, so that the gain and loss of electrons from the duskside and dawnside of a dipolarizing flux tube roughly balance. The ''dispersed injection'' feature is seen east of the dipolarization region. Our theory successfully explains the statistical differences in terms of magnetic local time location and peak intensity between spikes and injection events. Through the substorm event on 23 May 1998 we demonstrate that our theoretical predictions of riometer responses are very consistent with the observations. We highlight the potential of riometers in resolving the azimuthal extent and evolution of the dipolarization region, which provides a new ground-based technique of remote sensing the substorm process.

show abstract

Substorm dynamics revealed by ground observations of two-dimensional auroral structures on 9 October 2000

Cited by 8 publications

References 29 publications

Substorm onset: Current sheet avalanche and stop layer

Substorm onset: Current sheet avalanche and stop layer

Intensification of preexisting auroral arc at substorm expansion phase onset: Wave‐like disruption during the first tens of seconds

Azimuthal structures of substorm electron injection and their signatures in riometer observations

Contact Info

Product

Resources

About