Path-integrated gain of whistler-mode chorus in the magnetosphere by a kappa distribution

Abstract

The path-integrated gain of whistler-mode chorus is evaluated by the incorporation of a kappa distribution of energetic electrons and a realistic field-aligned density model of background electrons. Variations of temperature anisotropy and number density of energetic electrons along the magnetic latitude are derived based on the conservation of the first adiabatic invariant. Numerical simulation shows that a lower-band chorus has a much higher path-integrated gain than an upper-band chorus under the same conditions. During propagation towards higher latitudes, chorus waves grow to large amplitudes in the early stage but ultimately attenuate due to wave damping. The path-integrated gain is higher with the initial wave vector pointing toward lower L shells than toward higher L shells. Moreover, the energetic electron population has a significant influence on the path-integrated gain, and the wave gain is larger as the temperature anisotropy or the density of energetic electrons is enhanced. This result provides further understanding of the chorus wave propagation characteristics in space plasmas.