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AGU: Geophysical Research Letters

 

Index Terms

  • Planetology: Comets and Small Bodies: Composition
  • Planetology: Comets and Small Bodies: Interactions with solar wind plasma and fields
  • Planetology: Comets and Small Bodies: Plasma and MHD instabilities
  • Space Plasma Physics: Wave-particle interactions

Abstract

GEOPHYSICAL RESEARCH LETTERS, VOL. 13, NO. 8, PP. 825-828, 1986
doi:10.1029/GL013i008p00825

Hydromagnetic waves near O+ (OR H2O+) ion cyclotron frequency observed by Sakigake at the closest approach to comet Halley

Kiyohumi Yumoto

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

Takao Saito

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

Tomoko Nakagawa

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

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.

Received 2 June 1986; accepted 21 June 1986; .

Citation: Yumoto, K., T. Saito, and T. Nakagawa (1986), Hydromagnetic waves near O+ (OR H2O+) ion cyclotron frequency observed by Sakigake at the closest approach to comet Halley, Geophys. Res. Lett., 13(8), 825–828, doi:10.1029/GL013i008p00825.

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