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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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    Abstract

    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.

    Item Type: Article
    Journal or Publication Title: Journal of Geophysical Research
    Additional Information: Copyright (2008) American Geophysical Union. Further reproduction or electronic distribution is not permitted
    Uncontrolled Keywords: magnetometer DCS-publications-id ; art-945 ; DCS-publications-credits ; iono ; samnet ; DCS-publications-personnel-id ; 5
    Subjects:
    Departments: Faculty of Science and Technology > Engineering
    Faculty of Science and Technology > Physics
    ID Code: 26210
    Deposited By: Dr Steve Marple
    Deposited On: 08 Apr 2009 16:25
    Refereed?: Yes
    Published?: Published
    Last Modified: 24 Apr 2014 09:00
    Identification Number:
    URI: http://eprints.lancs.ac.uk/id/eprint/26210

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