Towards a synthesis of substorm electrodynamics: HF radar and auroral observations

Grocott, Adrian; Lester, M.; Parkinson, M. L.; Yeoman, T. K.; Dyson, P. L.; Devlin, John; Frey, H. U.

doi:10.5194/angeo-24-3365-2006

Cited by 18 publications

(21 citation statements)

References 89 publications

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“…The present results are consistent with the previous results of Kamide et al [1996], Opgenoorth and Pellinen [1998], Borälv et al [2000], Saka et al [2001], Grocott et al [2002, 2006], Liang et al [2004, 2006], and Provan et al [2004] in that ionospheric convection enhances, not reduces, in association with substorm onset. In the present study, we examined the timing of the convection change relative to substorm onset in more detail.…”

Section: Discussionsupporting

confidence: 93%

“… Bristow et al [2001, 2003] and Bristow and Jensen [2007] reported that ionospheric convection enhances during the growth phase but it reduces at onset. In contrast, some other previous studies concluded that ionospheric convection enhances at onset [e.g., Kamide et al , 1996; Opgenoorth and Pellinen , 1998; Grocott et al , 2002, 2006; Liang et al , 2004, 2006; Provan et al , 2004]. Borälv et al [2000] and Saka et al [2001] reported that ionospheric convection may enhance a few minutes before onset.…”

Section: Introductionmentioning

confidence: 74%

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Response of large‐scale ionospheric convection to substorm expansion onsets: A case study

et al. 2008

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[1] We have studied the response of large-scale ionospheric convection to substorm expansion onsets on the basis of two weak substorms of 1 May 2001, during which a large part of the dawn cell of the two-cell ionospheric convection pattern was monitored by the SuperDARN radars. Ionospheric convection began to enhance first in a localized region of the equatorward part of the dawn cell $2 minutes before the expansion onsets of both substorms and then enhanced in the entire dawn cell successively. The enhanced convection persisted throughout their expansion phase, possibly even near the footprint of a plasma sheet region without fast flows observed by Geotail. These observations suggest that ionospheric convection begins to enhance just before substorm expansion onset and then enhances in the entire cell, possibly regardless of the presence of fast earthward flows in the corresponding plasma sheet region of the magnetotail. The global enhancement of ionospheric convection is consistent with that of magnetotail convection, which also begins just before onset.

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Section: Discussionsupporting

confidence: 93%

Section: Introductionmentioning

confidence: 74%

Response of large‐scale ionospheric convection to substorm expansion onsets: A case study

et al. 2008

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“…7) suggests that the relevant current circuit was the downward Region 2 FAC, the poleward Pedersen current, and the upward Region 2 current. Closure via the zonal substorm current wedge and the meridional current system of Kamide et al (1994) (see Grocott et al, 2006) may also have played a role. The current circuit may also have consisted of thin FAC sheets located immediately equatorward and poleward of the AWFC, but neither the Iridium or DMSP satellite observations revealed evidence for their existence.…”

Section: Outstanding Issuesmentioning

confidence: 99%

An auroral westward flow channel (AWFC) and its relationship to field-aligned current, ring current, and plasmapause location determined using multiple spacecraft observations

Parkinson

Wild²,

Waters³

et al. 2007

Ann. Geophys.

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Abstract. An auroral westward flow channel (AWFC) is a latitudinally narrow channel of unstable F-region plasma with intense westward drift in the dusk-to-midnight sector ionosphere. AWFCs tend to overlap the equatorward edge of the auroral oval, and their life cycle is often synchronised to that of substorms: they commence close to substorm expansion phase onset, intensify during the expansion phase, and then decay during the recovery phase. Here we define for the first time the relationship between an AWFC, large-scale field-aligned current (FAC), the ring current, and plasmapause location. The Tasman International Geospace Environment Radar (TIGER), a Southern Hemisphere HF Super-DARN radar, observed a jet-like AWFC during ∼08:35 to 13:28 UT on 7 April 2001. The initiation of the AWFC was preceded by a band of equatorward expanding ionospheric scatter (BEES) which conveyed an intense poleward electric field through the inner plasma sheet. Unlike previous AWFCs, this event was not associated with a distinct substorm surge; rather it occurred during an interval of persistent, moderate magnetic activity characterised by AL∼ −200 nT. The four Cluster spacecraft had perigees within the dusk sector plasmasphere, and their trajectories were magnetically conjugate to the radar observations. The Waves of High frequency and Sounder for Probing Electron density by Relaxation (WHISPER) instruments on board Cluster were used to identify the plasmapause location. The Imager for Magnetopause-to-Aurora Global Exploration (IM-AGE) EUV experiment also provided global-scale observations of the plasmapause. The Cluster fluxgate magnetometers (FGM) provided successive measurements specifying the relative location of the ring current and filamentaryCorrespondence to: M. L. Parkinson (m.parkinson@latrobe.edu.au) plasma sheet current. An analysis of Iridium spacecraft magnetometer measurements provided estimates of large-scale ionospheric FAC in relation to the AWFC evolution. Peak flows in the AWFC were located close to the peak of a Region 2 downward FAC, located just poleward of the plasmapause. DMSP satellite observations confirmed the AWFC was located equatorward of the nightside plasmasheet, sometimes associated with ∼10 keV ion precipitation.

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“…Further studies using SuperDARN have produced mixed results, however, by providing evidence for both the excitation (e.g. Grocott et al, 2006;Provan et al, 2004) and reduction (e.g. Lyons et al, 2001;Bristow and Jensen, 2007) of the flows following substorm onset.…”

Section: Introductionmentioning

confidence: 99%

Superposed epoch analysis of the ionospheric convection evolution during substorms: onset latitude dependence

et al. 2009

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Abstract. Using data from the Super Dual Auroral Radar Network (SuperDARN) we investigate the ionospheric convection response to magnetospheric substorms. Substorms were identified using the Far Ultraviolet (FUV) instrument on board the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) spacecraft, and were then binned according to the magnetic latitude of their onset. A superposed epoch analysis of the ionospheric convection patterns for each onset-latitude bin was then performed using radar data for the interval 60 min before onset to 90 min after. It is found that lower onset-latitude substorms are associated with generally more enhanced convection than the higher latitude substorms, although they suffer from a significant localised reduction of the flow in the midnight sector during the expansion phase. Higher-latitude substorms are associated with a significant and rapid increase in the nightside convection following substorm onset, with all onset-latitude bins showing an enhancement over onset values by ∼60 min into the expansion phase. A rudimentary inspection of the concurrent auroral evolution suggests that the duration of the flow reduction following substorm onset is dependent on the strength and duration of the expansion phase aurora and its associated conductivity enhancement.

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Towards a synthesis of substorm electrodynamics: HF radar and auroral observations

Cited by 18 publications

References 89 publications

Response of large‐scale ionospheric convection to substorm expansion onsets: A case study

Response of large‐scale ionospheric convection to substorm expansion onsets: A case study

An auroral westward flow channel (AWFC) and its relationship to field-aligned current, ring current, and plasmapause location determined using multiple spacecraft observations

Superposed epoch analysis of the ionospheric convection evolution during substorms: onset latitude dependence

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