Auroral Kilometric Radiation Source Region Observations from ISIS 1

  1. S.-I. Akasofu and
  2. J.R. Kan
  1. Robert F. Benson

Published Online: 26 MAR 2013

DOI: 10.1029/GM025p0369

Physics of Auroral Arc Formation

Physics of Auroral Arc Formation

How to Cite

Benson, R. F. (1981) Auroral Kilometric Radiation Source Region Observations from ISIS 1, in Physics of Auroral Arc Formation (eds S.-I. Akasofu and J.R. Kan), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM025p0369

Author Information

  1. Laboratory for Planetary Atmospheres, Goddard Space Flight Center, Greenbelt, Maryland 20771

Publication History

  1. Published Online: 26 MAR 2013
  2. Published Print: 1 JAN 1981

ISBN Information

Print ISBN: 9780875900506

Online ISBN: 9781118664360



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The ISIS 1 satellite encounters the lower altitude portion of the auroral kilometric radiation (AKR) source region during high latitude apogee (3500 km) passes. The ISIS 1 ionospheric sounder detects AKR while determining both ambient and remote plasma conditions. This paper will review the ISIS 1 observations of the high frequency portion of the AKR spectrum, i.e., from the minimum frequency encountered for the extraordinary mode cut-off (∼450 kHz) to the upper frequency cut-off (∼800 kHz). AKR is found to be generated in the extraordinary mode just above the local cutoff frequency and to emanate nearly perpendicular to the magnetic field. It occurs within local depletions of electron density, where the ratio of plasma frequency to cyclotron frequency is less than 0.2. The density depletion is restricted to altitudes above about 2000 km, and the upper AKR frequency limit corresponds to the extraordinary cutoff frequency at this altitude. AKR is observed from ISIS 1 above the nighttime auroral zone over a wider extent in longitude than in latitude with an intense source region observed most often near 2200 magnetic local time and 70 invariant latitude. It is directly related to inverted V electron precipitation events, and particular features within the electron energy spectra are directly correlated with source region AKR encounters. Simultaneous wave and particle measurements within the source region indicate an electron-to-wave energy conversion efficiency of the order of 0.1 to 1%.