AKR breakup and auroral particle acceleration at substorm onset

Morioka, A. and Miyoshi, Y. and Tsuchiya, F. and Misawa, H. and Yumoto, K. and Parks, G.K. and Anderson, R.R. and Menietti, J.D. and Donovan, E.F. and Honary, Farideh and Spanswick, E. (2008) AKR breakup and auroral particle acceleration at substorm onset. Journal of Geophysical Research, 113 (A9). A09213. ISSN 0148-0227

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The dynamical behavior of auroral kilometric radiation (AKR) is investigated in connection with auroral particle acceleration at substorm onsets using high-time-resolution wave spectrograms provided by Polar/PWI electric field observations. AKR develops explosively at altitudes above a preexisting low-altitude AKR source at substorm onsets. This “AKR breakup” suggests an abrupt formation of a new field-aligned acceleration region above the preexisting acceleration region. The formation of the new acceleration region is completed in a very short time (amplitude increases 10,000 times in 30 seconds), suggesting that the explosive development is confined to a localized region. AKR breakups are usually preceded (1–3 minutes) by the appearance and/or gradual enhancement of the low-altitude AKR. This means that the explosive formation of the high-altitude electric field takes place in the course of the growing low-altitude acceleration. The development of the low-altitude acceleration region is thus a necessary condition for the ignition of the high-altitude bursty acceleration. The dH/dt component from a search-coil magnetometer at ground shows that a few minutes prior to substorm onsets, the quasi-DC component begins a negative excursion that is nearly synchronized with the start of the gradual enhancement of the low-altitude AKR, indicating a precursor-like behavior for the substorm. This negative variation of dH/dt suggests an exponentially increasing ionospheric current induced by the upward field-aligned current. At substorm onsets, the decrease in the quasi-DC variation of dH/dt further accelerates, indicating a sudden reinforcement of the field-aligned current.

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Journal Article
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Journal of Geophysical Research
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Copyright (2008) American Geophysical Union. Further reproduction or electronic distribution is not permitted
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08 Apr 2009 15:25
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21 Jul 2024 00:15