Universal time control of AKR: Earth is a spin-modulated variable radio source

Akira Morioka, Yoshizumi Miyoshi, Satoshi Kurita, Yasumasa Kasaba, Vassilis Angelopoulos, Hiroaki Misawa, Hirotsugu Kojima, James P. McFadden

Research output: Contribution to journalArticlepeer-review

7 Citations (Scopus)


Auroral kilometric radiation (AKR) is known to be transient emissions generated by rapidly accelerated electrons together with sudden auroral activation in the polar magnetosphere. In contrast, the characteristics and relationship with the auroral acceleration of rather continuous AKR emissions are not well understood. We examine the emission using long-term data and report that the continuous AKR emission frequency changes with universal time (UT) as the Earth rotates, indicating that the Earth is a spin-modulated variable radio source. The observed UT variation of AKR frequency means that the acceleration altitude changes periodically with planetary rotation. The observations indicate that the diurnal wobble of the tilted geomagnetic field in the solar wind flow alters the magnetosphere-ionosphere (M-I) coupling state in the polar magnetosphere, giving rise to periodic variation of auroral particle acceleration altitude. These observations of planetary radio wave properties provide insight into the physics of planetary particle acceleration. Key Points We found universal time control of AKR frequency. Earth is a spin-modulated variable source. Acceleration altitude changes periodically.

Original languageEnglish
Pages (from-to)1123-1131
Number of pages9
JournalJournal of Geophysical Research: Space Physics
Issue number3
Publication statusPublished - 2013 Mar


  • AKR frequency variation
  • spin modulation
  • UT control
  • Variable radio source


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