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Ann. Geophys., 17, 623-630, 1999
www.ann-geophys.net/17/623/1999/
© European Geosciences Union 1999
Stability of stationary and time-varying nongyrotropic particle distributions
A. L. Brinca
Centro de F. de Plasmas, Instituto Superior Técnico, P-1096 Lisboa Codex, Portugal
Correspondence to: ebrinca@beta.ist.utl.pt
Abstract. The ubiquity of nongyrotropic particle
populations in space plasmas warrants the study of their characteristics, in
particular their stability. The unperturbed nongyrotropic distribution functions
in homogeneous media without sources and sinks (closed phase space) must be
rotating and time-varying (TNG), whereas consideration of open phase spaces
allows for the occurrence of homogeneous and stationary distributions (SNG). The
free energy brought about by the introduction of gyrophase organization in a
particle population can destabilize otherwise thoroughly stable magnetoplasmas
(or, a fortiori, enhance pre-existing gyrotropic instabilities) and feed
intense wave growth both in TNG and SNG environments: The nongyrotropic
(electron or ion) species can originate unstable coupling among the gyrotropic
characteristic waves. The stability properties of these two types of homogeneous
nongyrotropy shall be contrasted for parallel (with respect to the ambient
magnetic field) and perpendicular propagation, and their potential role as wave
activity sources shall be illustrated resorting to solutions of the appropriate
dispersion equations and numerical simulations.
Key words. Space plasma physics (waves and
instabilities) · Magnetospheric physics (plasma waves and instabilities) ·
Interplanetary physics (plasma waves and turbulence)
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