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Title: Helium cyclotron resonance within the earth's magnetosphere

Abstract

A histogram of electromagnetic Alfven/ion cyclotron wave frequencies, sampled within the geostationary enviroment and normalized by the equatorial proton cyclotron frequency, shows a dramatic gap centered near the helium (He/sup +/) cyclotron frequency. Also, strongly cyclotron phase bunched helium ions (20--200 eV) have been observed directly within the vicinity of wave environments. These observations are interpreted as resulting from the absorption of the waves through cyclotron resonance by cool ambient populations of helium ions.

Authors:
; ;
Publication Date:
Research Org.:
Geophysics AK-50, University of Washington, Seattle, Washington 98195
OSTI Identifier:
6617012
Resource Type:
Journal Article
Resource Relation:
Journal Name: Geophys. Res. Lett.; (United States); Journal Volume: 8:1
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; MAGNETOSPHERE; CYCLOTRON RESONANCE; ALFVEN WAVES; HELIUM IONS; ION WAVES; PROTONS; RADIATION BELTS; BARYONS; CHARGED PARTICLES; EARTH ATMOSPHERE; ELEMENTARY PARTICLES; FERMIONS; HADRONS; HYDROMAGNETIC WAVES; IONS; NUCLEONS; PLASMA WAVES; RESONANCE 640203* -- Atmospheric Physics-- Magnetospheric Phenomena-- (-1987)

Citation Formats

Mauk, B.H., McIlwain, C.E., and McPherron, R.L.. Helium cyclotron resonance within the earth's magnetosphere. United States: N. p., 1981. Web. doi:10.1029/GL008i001p00103.
Mauk, B.H., McIlwain, C.E., & McPherron, R.L.. Helium cyclotron resonance within the earth's magnetosphere. United States. doi:10.1029/GL008i001p00103.
Mauk, B.H., McIlwain, C.E., and McPherron, R.L.. 1981. "Helium cyclotron resonance within the earth's magnetosphere". United States. doi:10.1029/GL008i001p00103.
@article{osti_6617012,
title = {Helium cyclotron resonance within the earth's magnetosphere},
author = {Mauk, B.H. and McIlwain, C.E. and McPherron, R.L.},
abstractNote = {A histogram of electromagnetic Alfven/ion cyclotron wave frequencies, sampled within the geostationary enviroment and normalized by the equatorial proton cyclotron frequency, shows a dramatic gap centered near the helium (He/sup +/) cyclotron frequency. Also, strongly cyclotron phase bunched helium ions (20--200 eV) have been observed directly within the vicinity of wave environments. These observations are interpreted as resulting from the absorption of the waves through cyclotron resonance by cool ambient populations of helium ions.},
doi = {10.1029/GL008i001p00103},
journal = {Geophys. Res. Lett.; (United States)},
number = ,
volume = 8:1,
place = {United States},
year = 1981,
month = 1
}
  • The ATS-6 geostationary satellite has observed many examples of propagating, electromagnetic Alfven/ion cyclotron waves in both plasma particle and magnetic field data. These waves have been viewed predominantly near the afternoon and dusk regions of the earth's magnetosphere with normalized frequencies (..omega../..cap omega../sub H//sup +/) ranging between 0.05 and 0.5. Viewed from an average geomagnetic latitude of +10/sup 0/, the waves have only been observed to propagate northward, suggesting that they are generated within the equatorial or minimum BETA regions. Two wave events have been chosen for detailed analysis. Both events appeared coincidentally with the encounter of cool plasma populationsmore » (5 eV) which joined the hot populations already present (10--40 keV). These coincidences suggest the popular, yet largely untested, electromagnetic ion cyclotron instability as the wave generation mechanism. As a test of this hypothesis, ion cyclotron amplification profiles are obtained by evaluating the linear growth rate integrals under the measured, anisotropic hot ion distributions. The measured frequencies for both of the chosen events are in good agreement with the quite restricted values which correspond to the peaks of the amplification profiles. As a result of magnetic field inhomogeneities, the interactions remain within the linear regime.« less
  • In this report, the authors consider the amplification of electromagnetic ion cyclotron waves along a geomagnetic field line in the multicomponent magnetosphere, assuming that the waves propagate parallel to the background magnetic field. The find it is possible for the ring-current protons (energy {approximately} 10-100 keV), which supply the free energy to stimulate the waves, to resonate with the waves not only in the equatorial region but also off the equator. An instability, caused by a thermal anisotropy, may occur in separated regions on and/or off the equator. The positions of the source regions along the wave path depend onmore » the concentration of cold heavy ion species. The significant off-equator source regions may be located at geomagnetic latitudes where the waves, with frequencies greater than the He{sup +} gyrofrequency on the equator, are in a local He{sup +} pass band.« less