Weak electrostatic waves near the upper hybrid frequency: A comparison between theory and experiment

Journal Article · Wed Apr 01 04:00:00 EST 1987 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/JA092iA04p03243· OSTI ID:5510558

Horne, R B ^[1]; Christiansen, P J; Gough, M P ^[2]

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1. Natural Environment Research Council, Cambridge (United Kingdom)
2. Univ. of Sussex, Brighton (United Kingdom)

Two types of generating mechanisms have been proposed to explain the observations of weak electrostatic waves near the local upper hybrid frequency f{sub uh}. In this paper data from the wave and plasma diagnostic experiments on GEOS 1 are presented with simultaneously observed particle data in an attempt to identify the generating mechanism.The electron data contain two sources of free energy: a highly anisotropic pancake' distribution in the warm (20 eV to {approximately}1 keV) plasma and a loss cone type distribution in the hot (>few keV) plasma. This leads the authors to consider a coherent generating mechanism. A model of the plasma distribution, with cold, warm and hot components is constructed and linear instability calculations are presented. It is shown that the relatively large resonant perpendicular velocities in the loss cone distribution generate instabilities at small perpendicular wave numbers preferentially in the upper hybrid band since the wave frequency can lie midway between the gyroharmonics where cyclotron damping is reduced. The calculations are able to reproduce the spectral characteristics observed by previous spacecraft over a range of cold plasma densities. The temporal growth rates are comparable to those obtained previously for strong electrostatic emissions near f{sub uh}, but it is shown that the unstable wave number region is an order of magnitude smaller. Thus it is argued that the waves remain weak since they are quickly refracted out of resonance.

• OSTI ID: 5510558
• Journal Information: Journal of Geophysical Research; (United States), Journal Name: Journal of Geophysical Research; (United States) Vol. 92:A4; ISSN JGREA; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

661320* -- Auroral
Ionospheric
& Magnetospheric Phenomena-- (1992-)
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ANISOTROPY
COLD PLASMA
DISTRIBUTION
EARTH ATMOSPHERE
EARTH MAGNETOSPHERE
ELECTRONS
ELEMENTARY PARTICLES
ENERGY
FERMIONS
FREE ENERGY
GEOS SATELLITES
LEPTONS
LOSS CONE
MATHEMATICAL MODELS
PHYSICAL PROPERTIES
PLASMA
PLASMA DENSITY
PLASMA WAVES
SATELLITES
SCATTERING
SPATIAL DISTRIBUTION
THERMODYNAMIC PROPERTIES