Hydromagnetic Waves Near O+ (OR H2O+) Ion Cyclotron Frequency Observed by Sakigake at the Closest Approach to Comet Halley

  1. Thomas J. Birmingham and
  2. Alexander J. Dessler
  1. Kiyohumi Yumoto,
  2. Takao Saito and
  3. Tomoko Nakagawa

Published Online: 19 MAR 2013

DOI: 10.1029/SP027p0107

Comet Encounters

Comet Encounters

How to Cite

Yumoto, K., Saito, T. and Nakagawa, T. (1988) Hydromagnetic Waves Near O+ (OR H2O+) Ion Cyclotron Frequency Observed by Sakigake at the Closest Approach to Comet Halley, in Comet Encounters (eds T. J. Birmingham and A. J. Dessler), American Geophysical Union, Washington, D.C.. doi: 10.1029/SP027p0107

Author Information

  1. Onagawa Magnetic Observatory and Geophysical Institute, Tohoku University, Sendai 980, Japan

Publication History

  1. Published Online: 19 MAR 2013
  2. Published Print: 1 JAN 1988

ISBN Information

Print ISBN: 9780875902395

Online ISBN: 9781118668757

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Keywords:

  • Closest approach;
  • Comet Halley;
  • Hydromagnetic (HM) waves;
  • Plasma wave probe (PWP);
  • Solar wind

Summary

Long-period HM waves with 150–380 s periods were observed by Sakigake at 7×106 km upstream from comet Halley. The wave amplitudes were as great as ∼2 nT peak to peak. The long-period waves were of an approximately linearly polarized transverse mode and propagated parallel to the ambient magnetic field. Dominant periods of the waves were found to be consistent with the local O+ (or H2O+) cyclotron period and to change as a function of the ambient magnetic field. The long-period HM waves are believed to be excited by a resonant instability with high-energy cometary heavy ions. The necessary cometary ion density for excitation at a distance of 7×106 km from the comet can be inferred to be of the order of 10−3 - 10−4 cm−3 for 101–102 keV O+ (or H2O+) ions.