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Geophysical Monograph Series

 

Keywords

  • Plasma waves—Congresses
  • Magnetospheres—Congresses
  • Comets—Congresses

Index Terms

  • 6060 Planetology: Comets and Small Bodies: Radiation and spectra
  • 6050 Planetology: Comets and Small Bodies: Plasma and MHD instabilities
  • 6025 Planetology: Comets and Small Bodies: Interactions with solar wind plasma and fields

Article

GEOPHYSICAL MONOGRAPH SERIES, VOL. 53, PP. 13-29, 1989

Ultra-low frequency waves at comets

Martin A. Lee

Institute for the Study of Earth, Oceans and Space, University of New Hampshire, Durham, NH 03824


This paper is a review of the observations and theory of ultra-low frequency (ULF) waves or turbulence (spacecraft frequencies less than 1 Hz) upstream of comets with an emphasis on the region upstream of the cometary bow wave. It attempts to be comprehensive in its coverage of the literature through Spring, 1988. First the general morphology of the cometary foreshock with its pickup ion and ULF wave distributions is described briefly. The observations of the ULF waves at comet Giacobini-Zinner by the ICE spacecraft and at comet Halley by the Giotto, Vega and Sakigake spacecraft are then reviewed. The major spectral feature at ∼0.01 Hz is shown to arise from cyclotron resonance of the waves with watergroup pickup ions. The stability analysis is presented for hydromagnetic and whistler waves propagating parallel to the ambient magnetic field in the presence of narrow and broad pickup ion ring distributions. The growth rate of the right-hand circularly polarized sunward propagating hydromagnetic wave is sufficient to account for the spectral feature at ∼0.01 Hz. Instabilities which could account for the 0.1–1 Hz wave packets observed at comet Giacobini-Zinner are reviewed but none appears to be promising. The quasilinear theory of the pickup ion-ULF wave interaction is shown to account rather well for ULF wave intensities near the cometary bow waves of the two comets. Finally work on the nonlinear evolution of the ∼0.01 Hz ULF waves is reviewed and found to provide a plausible origin for the 0.1–1 Hz wave packets.

Citation: Lee, M. A. (1989), Ultra-low frequency waves at comets, in Plasma Waves and Instabilities at Comets and in Magnetospheres, Geophys. Monogr. Ser., vol. 53, edited by B. T. Tsurutani and H. Oya, pp. 13–29, AGU, Washington, D. C., doi:10.1029/GM053p0013.

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