Abstract Threshold conditions for the ion cyclotron instability, due to a distorted ion velocity distribution in the auroral F-region ionosphere, and the quasilinear evolution of the distribution function, are investigated. It is found that the critical value of the ion drift parameter for the resonant ion species is between 1.3 and 1.4 in most cases, becoming considerably larger only if the fractional concentration of the resonant species is less than about 20 % or if the field-parallel ion temperature for the non-resonant species is low compared with the resonant species. Also, the threshold is independent of the degree of distortion of the non-resonant ion velocity distribution. Velocity space diffusion driven by ion cyclotron waves becomes important if the ratio of the electrostatic energy and the ion thermal energy (the weak turbulence parameter) is of the order of 10−6 Δk | (m−1) or more, where Δk | is the width of the wave spectrum in k |. The steady state velocity distribution function for a given value of parallel velocity lies between two extremes: the Raman et al. -type distribution with a large positive slope in field-perpendicular velocity (ν ⊥) and a distribution function with the positive slope replaced by a plateau of the size , where is the resonant ion (angular) gyrofrequency and k ⊥ the perpendicular wavenumber which dominates the spectrum.
Microinstabilities driven by non-thermal plasma in the high-latitude F-region
Advances in Space Research ; 10 , 6 ; 149-152
1989-01-01
4 pages
Article (Journal)
Electronic Resource
English
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