Adiabatic-drift-loss modification of the electromagnetic loss-cone instability for anisotropic plasma |
| |
Authors: | B Juhl R A Treumann |
| |
Institution: | (1) Institut für Extraterrestrische Physik, Max-Planck-Institut für Physik und Astrophysik, Garching b. München, West Germany;(2) Gruppe für Radioastronomie, Eidgenössische Technische Hochschule Zürich, Switzerland |
| |
Abstract: | Observation of the adiabatic behaviour of energetic particle pitch-angle distributions in the magnetosphere (Lyons, 1977, and others) in the past indicated the development of pronounced minima or drift-loss cones on the pitch-angle distributions centred at 90° in connection with storm-time changes in magnetospheric convection and magnetic field. Using a model of a drift-modified loss-cone distribution (MLCD) of the butterfly type, the linear stability of electromagnetic whistler or ion-cyclotron waves propagating parallel to the magnetic field has been investigated. The instability is shown to be quenched at high frequencies <
m
=A/(A+1), whereA is the thermal anisotropy. This quenching becomes stronger the higher are the respective parallel hot particle thermal velocityA
h and cold plasma densityn
c
. Particles around pitch-angles 90° are identified as generating electromagnetic cyclotron waves near the marginally stable frequency
m
. It is concluded that the absence of electromagnetic VLF and ELF noise during times when MLCD develops is the result of the shift of the unstable spectrum to low frequencies. |
| |
Keywords: | |
本文献已被 SpringerLink 等数据库收录! |
|