A substorm model with onset location tied to an auroral arc

Lui, A. T. Y.; Murphree, J. S.

doi:10.1029/98gl00758

Cited by 41 publications

(18 citation statements)

References 23 publications

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“… Akasofu [1964] and Lui and Murphree [1998] showed on the basis of ground‐based auroral observations that substorm initial brightening starts at a point in the preexisting auroral arc. On the other hand, Lyons et al [2002] claimed that an auroral breakup does not generally occur along one of the preexisting arcs but instead occurs along a thin breakup arc that forms equatorward of all growth phase arcs a few minutes prior to onset.…”

Section: Discussionmentioning

confidence: 99%

Dual structure of auroral acceleration regions at substorm onsets as derived from auroral kilometric radiation spectra

et al. 2007

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[1] Two sources of auroral kilometric radiation (AKR) and their development prior to and during substorms were identified from high-time-resolution spectrograms provided by Polar/PWI ac electric field observations and were investigated in connection with the auroral acceleration process. One source is a low-altitude source region corresponding to middle-frequency AKR (MF-AKR), and the other is a high-altitude source region corresponding to low-frequency AKR (LF-AKR). The former appears during the substorm growth phase in the altitude range of 4000-5000 km and is active both before and after substorm onset. A few minutes before the onset, the intensity of this source gradually increases, showing precursor-like behavior. It does not change drastically at the onset and is mostly insensitive to it. At Pi 2 onset, in contrast, high-altitude AKR appears abruptly with intense power in a higher and wider altitude range of 6000 to 12,000 km. The increase in its power is explosive (increasing 1000 times within 20 s), suggesting the abrupt growth of the parallel electric fields that cause bursty auroral electron beams. The statistically derived probability of both sources existing at substorm onset is $70%, indicating that this duality of AKR sources is a common feature of substorms. The highaltitude source and related transient acceleration at substorm onset are apparently due to (1) intrinsically local instabilities such as current-driven instabilities or (2) transient short wavelength Alfvén waves coming from the magnetosphere. The low-altitude source, which is fairly stable and insensitive to substorm onset, may belong to the global quasistatic potential distribution over the auroral oval, which involves a large-scale inverted-V structure and a quasi-steady field-aligned current.

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Section: Discussionmentioning

confidence: 99%

Dual structure of auroral acceleration regions at substorm onsets as derived from auroral kilometric radiation spectra

et al. 2007

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“…However, was it actually part of the process of triggering the substorm? For example, Lui and Murphree (1998) recently proposed that cross-tail current disruption occurs via the cross-field current instability (CCI) when the current is driven to a critical value during an appropriate half-cycle of a MHD field-line resonant wave. This occurs at the inner edge of the plasma sheet, near where AWFCs occur.…”

Section: Discussionmentioning

confidence: 99%

On the lifetime and extent of an auroral westward flow channel (AWFC) observed during a magnetospheric substorm

Parkinson

Pinnock

et al. 2003

Ann. Geophys.

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Abstract.A −190-nT negative bay in the geomagnetic X component measured at Macquarie Island (−65 • ) showed that an ionospheric substorm occurred during 09:58 to 11:10 UT on 27 February 2000. Signatures of an auroral westward flow channel (AWFC) were observed nearly simultaneously in the backscatter power, LOS Doppler velocity, and Doppler spectral width measured using the Tasman International Geospace Environment Radar (TIGER), a Southern Hemisphere HF SuperDARN radar. Many of the characteristics of the AWFC were similar to those occurring during a polarisation jet (PJ), or subauroral ion drift (SAID) event, and suggest that it may have been a precursor to a fully developed, intense westward flow channel satisfying all of the criteria defining a PJ/SAID. A beamswinging analysis showed that the westward drifts (poleward electric field) associated with the flow channel were very structured in time and space, but the smoothed velocities grew to ∼800 m s −1 (47 mV m −1 ) during the 22-min substorm onset interval 09:56 to 10:18 UT. Maximum westward drifts of >1.3 km s −1 (>77 mV m −1 ) occurred during a ∼5-min velocity spike, peaking at 10:40 UT during the expansion phase. The drifts decayed rapidly to ∼300 m s −1 (18 mV m −1 ) during the 6-min recovery phase interval, 11:04 to 11:10 UT. Overall, the AWFC had a lifetime of 74 min, and was located near −65 • in the evening sector west of the Harang discontinuity. The large westward drifts were confined to a geographic zonal channel of longitudinal extent >20 • (>1.3 h magnetic local time), and latitudinal width ∼2 • . Using a half-width of ∼100 km in latitude, the peak electric potential was >7.7 kV. However, a transient velocity of >3.1 km s −1 with potential >18.4 kV was observed further poleward at the end of the recovery phase. Auroral oval boundaries determined using DMSP measurements suggestCorrespondence to: M. L. Parkinson (m.parkinson@latrobe.edu.au) the main flow channel overlapped the equatorward boundary of the diffuse auroral oval. During the ∼2-h interval following the flow channel, an ∼3 • wide band of scatter was observed drifting slowly toward the west, with speeds gradually decaying to ∼50 m s −1 (3 mV m −1 ). The scatter was observed extending past the Harang discontinuity, and had Doppler signatures characteristic of the main ionospheric trough, implicating the flow channel in the further depletion of F-region plasma. The character of this scatter was in contrast with the character of the scatter drifting toward the east at higher latitude.Key words. Ionosphere (auroral ionosphere; electric fields and currents; ionosphere-magnetospehere interactions) Magnetospheric physics (storms and substorms)

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“…1 It has been suggested that plasma instabilities are responsible for the perturbations of these field lines, driven by large plasma pressure gradients in the neighborhood of the equatorial plane where the field line curvature is large. 2,3 In fact the suggestion that plasma pressure driven instabilities operate in the geosynchronous substorm region of the magnetosphere goes back much further to an earlier publication by Roux et al 4 At 6-10 Earth radii, the magnetospheric plasma is essentially collisionless and the plasma beta ͑␤͒ at the equatorial plane is typically larger than unity ͑␤ϭ8p/B 2 Ͼ1 where p is the plasma pressure and B the magnetic field magnitude͒. Thus, to test the relevance of the above-given suggestion, it is necessary to establish the conditions required for the onset of plasma instabilities in collisionless high beta magnetic dipole configurations and to determine whether such conditions are met in the Earth's magnetosphere.…”

Section: Introductionmentioning

confidence: 99%

Low frequency stability of geotail plasma

Wong¹,

Horton²,

Dam³

et al. 2001

Physics of Plasmas

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The local flux surface stability of magnetic dipole configurations is investigated in the magnetohydrodynamic (MHD) and drift frequency regimes. Solutions of the plasma equations in the very high beta limit are discussed. A novel procedure is developed for discussing stability in terms of the frequency ratio: the orbit averaged ion drift frequency divided by the ion diamagnetic frequency. This procedure is used to examine the stability of magnetospheric flux surfaces in the neighborhood of the equatorial plane at 6–10 Earth radii (where the plasma beta is ∼5 and where the onset of plasma instabilities may be responsible for triggering magnetic storms) with the following results: (1) MHD ballooning modes are predicted to be stable unless κvxp⩽2/5 where xp is the plasma pressure gradient scale length and κv the vacuum field line curvature at the equatorial plane; (2) drift modes may also be unstable unless η∼2/3, where η is the density gradient scale length divided by the temperature gradient scale length.

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A substorm model with onset location tied to an auroral arc

Cited by 41 publications

References 23 publications

Dual structure of auroral acceleration regions at substorm onsets as derived from auroral kilometric radiation spectra

Dual structure of auroral acceleration regions at substorm onsets as derived from auroral kilometric radiation spectra

On the lifetime and extent of an auroral westward flow channel (AWFC) observed during a magnetospheric substorm

Low frequency stability of geotail plasma

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