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AKR breakup and auroral particle acceleration at substorm onset

Research output: Contribution to journalJournal article

Published

  • A. Morioka
  • Y. Miyoshi
  • F. Tsuchiya
  • H. Misawa
  • K. Yumoto
  • G.K. Parks
  • R.R. Anderson
  • J.D. Menietti
  • E.F. Donovan
  • Farideh Honary
  • E. Spanswick
<mark>Journal publication date</mark>9/09/2008
<mark>Journal</mark>Journal of Geophysical Research
IssueA9
Volume113
PagesA09213
<mark>Original language</mark>English

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.

Bibliographic note

Copyright (2008) American Geophysical Union. Further reproduction or electronic distribution is not permitted