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Optical characterization of the growth and spatial structure of a substorm onset arc

Rae, I. J., Watt, C. E. J., Mann, I. R., Murphy, K. R., Samson, J. C., Kabin, K. and Angelopoulos, V. (2010) Optical characterization of the growth and spatial structure of a substorm onset arc. Journal of Geophysical Research, 115. A10222. ISSN 0148-0227

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To link to this item DOI: 10.1029/2010JA015376

Abstract/Summary

We present a detailed case study of the characteristics of auroral forms that constitute the first ionospheric signatures of substorm expansion phase onset. Analysis of the optical frequency and along-arc (azimuthal) wave number spectra provides the strongest constraint to date on the potential mechanisms and instabilities in the near-Earth magnetosphere that accompany auroral onset and which precede poleward arc expansion and auroral breakup. We evaluate the frequency and growth rates of the auroral forms as a function of azimuthal wave number to determine whether these wave characteristics are consistent with current models of the substorm onset mechanism. We find that the frequency, spatial scales, and growth rates of the auroral forms are most consistent with the cross-field current instability or a ballooning instability, most likely triggered close to the inner edge of the ion plasma sheet. This result is supportive of a near-Earth plasma sheet initiation of the substorm expansion phase. We also present evidence that the frequency and phase characteristics of the auroral undulations may be generated via resonant processes operating along the geomagnetic field. Our observations provide the most powerful constraint to date on the ionospheric manifestation of the physical processes operating during the first few minutes around auroral substorm onset.

Item Type:Article
Refereed:Yes
Divisions:No Reading authors. Back catalogue items
Faculty of Science > School of Mathematical, Physical and Computational Sciences > Department of Meteorology
ID Code:32814
Uncontrolled Keywords:field line resonance; azimuthal structuring; auroral beads
Publisher:American Geophysical Union

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