Analysis of auroral morphology: Substorm precursor and onset on January 10, 1997

Germany, G. A.; Parks, G. K.; Ranganath, H.; Elsen, R.; Richards, P. G.; Swift, Wesley R.; Spann, J. F.; Brittnacher, M.

doi:10.1029/98gl01220

Cited by 33 publications

(13 citation statements)

References 8 publications

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“…Interestingly, this negative bay is not associated with an auroral breakup. Actually, the size of the polar cap started to increase after 0230 UT in response to the sharp southward turning of the IMF at 0220 UT, and Germany et al [1998] interpreted this time period as the growth phase of a substorm that commenced at 0343 UT.…”

Section: Observationsmentioning

confidence: 99%

Investigation of external triggering of substorms with Polar ultraviolet imager observations

et al. 2003

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The triggering mechanism(s) for the substorm expansion phase onset is one of the outstanding issues in magnetospheric physics. Previous studies have shown that an impingement of the high solar wind dynamic pressure may lead to the expansion phase onset of a substorm. These previous studies typically used a negative magnetic bay as the main proxy for a substorm, but we now know that some magnetic bays are associated not with substorms but with the enhancement of convection. Therefore it is reasonable to cast doubts on the compression trigger mechanism. In this study we use classical substorm onsets, “auroral breakups,” which are the most reliable substorm onset indicator when identified with global auroral images, to reinvestigate this issue. We examine 43 interplanetary shock events that occurred between 1996 and 1999 with simultaneous global auroral images from the Polar ultraviolet imager images and the auroral electrojet indices. It is found, indeed, that ∼52% of the shocks produce magnetic bays (AL < −100 nT). While most of the shocks enhance auroral luminosities, only 4 events (∼9%) appear to have an auroral breakup preceded by an SSC/SI by 20 min (two events by 10 min). These results strongly indicate interplanetary shocks can produce negative magnetic bays but not auroral breakups (thus christened “compression bays”). An examination of precisely timed interplanetary magnetic field (IMF) during 11 substorms that occurred near the shock‐induced SSCs/SIs indicates that northward turnings of IMF occurred more than 50% of time. Given such a low probability, it is concluded that shock compression is not likely to trigger substorms but enhances magnetospheric currents and auroral particle precipitation. In line with many previous study results, on the other hand, the northward turnings of IMF can be a plausible substorm triggering mechanism.

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Section: Observationsmentioning

confidence: 99%

Investigation of external triggering of substorms with Polar ultraviolet imager observations

et al. 2003

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“…Furthermore, the configuration of the auroral boundaries is a good indicator of the solar wind‐magnetosphere‐ionosphere coupling, in which the auroral poleward boundary is a good proxy for the open‐close field line separatrix associated with the earthward burst flow from the tail plasma sheet, and the equatorward boundary often relates to the earthward edge of the main plasma sheet. The configuration of auroral poleward and equatorward boundaries is highly dynamic during storms and/or the substorms [ Germany et al , ].…”

Section: Introductionmentioning

confidence: 99%

A new auroral boundary determination algorithm based on observations from TIMED/GUVI and DMSP/SSUSI

Ding

Zhang

et al. 2017

JGR Space Physics

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An automatic auroral boundary determination algorithm is proposed in this study based on the partial auroral oval images from the Global Ultraviolet Imager (GUVI) aboard the Thermosphere–Ionosphere‐Mesosphere Energetics and Dynamics satellite and the Special Sensor Ultraviolet Spectrographic Imager (SSUSI) aboard the Defense Meteorological Satellite Program (DMSP F16). This algorithm based on the fuzzy local information C‐means clustering segmentation can be used to extract the auroral oval poleward and equatorward boundaries from merged images with filled gaps from both GUVI and SSUSI. Both extracted poleward and equatorward boundary locations are used to fit the global shape of the auroral oval with a off‐center quasi‐elliptical fitting technique. Comparison of the extracted auroral oval boundaries with those identified from the DMSP SSJ observations demonstrates that this new proposed algorithm can reliably be used to construct the global configuration of auroral ovals under different geomagnetic activities at different local times. The statistical errors of magnetic latitudes of the fitted auroral oval boundaries were generally less than 3° at 2 sigma and indicate that the the fitted boundaries agree better with b2e and b5e than b1e and b6 boundaries. This proposed algorithm provides us with a useful tool to extract the global shape and position of the auroral oval from the partial auroral images.

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“…In some cases, these boundaries have been identified explicitly with the polar cap boundary [Makita et al, 1985;Troshichev et al, 1996]. Satellite-borne auroral imagers have been used extensively to identify the polar cap boundary with the poleward auroral emission (PAE) boundary [Craven and Frank, 1987;Frank and Craven, 1988;Lassen and Danielson, 1989;Elphinstone et al, 1990;Germany et al, , 1998Kamide et al, 1999;Brittnacher et al, 1999]. The advantages of this method are obvious: a global perspective of the polar cap, at reasonably good temporal and spatial resolution, and from a single data source.…”

Section: Introductionmentioning

confidence: 99%

The nightside poleward boundary of the auroral oval as seen by DMSP and the Ultraviolet Imager

Baker¹,

Clauer²,

Ridley³

et al. 2000

J. Geophys. Res.

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Abstract. A lack of reliable error estimates for poleward auroral emission (PAE) boundaries derived from satellite-borne auroral imagers has hampered the application of these instruments in quantitative magnetospheric energy balance and substorm analysis. In this study, PAE boundaries from Polar Ultraviolet Imager (UVI) images are compared with precipitation boundaries from Defense Meteorological Satellite Program (DMSP) satellite spectrograms. In particular, the study quantifies the accuracy with which UVI images can be used to reproduce the DMSP poleward auroral oval (b5e) boundary. Most of the DMSP b5e boundaries were obtained in the evening sector. It has been determined that a UVI PAE boundary defined by a fixed ratio to the maximum in the auroral oval at each magnetic local time correlates better with the DMSP b5e boundary than one defined by a constant brightness threshold (

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Analysis of auroral morphology: Substorm precursor and onset on January 10, 1997

Cited by 33 publications

References 8 publications

Investigation of external triggering of substorms with Polar ultraviolet imager observations

Investigation of external triggering of substorms with Polar ultraviolet imager observations

A new auroral boundary determination algorithm based on observations from TIMED/GUVI and DMSP/SSUSI

The nightside poleward boundary of the auroral oval as seen by DMSP and the Ultraviolet Imager

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