Respective role of the cold and warm plasma densities on the generation mechanism of ULF waves in the magnetosphere

Abstract

Amplification of ion cyclotron waves is studied for different values of the ratios between the cold and warm plasma densities and between the resonant and parallel thermal velocities. Growth rates are then optimized for any set of magnetospheric parameters. The role of the cold plasma density is examined. It is shown that there exists a preferential value of the cold plasma density which gives the largest maximum growth rate. An increase of the warm plasma density always leads to an increase of the maximum growth rate. The L-value for which particles of a given initial energy are more likely to be precipitated during their inward penetration is also investigated. The model chosen to represent the radial variation of the anisotropy is shown to be of vital importance.