Warm plasma effects on electromagnetic ion cyclotron wave MeV electron interactions in the magnetosphere

The full kinetic linear dispersion relation in a warm plasma with He+ and O+ ions is used to estimate the minimum resonant electron energies required for resonant scattering of relativistic electrons by electromagnetic ion cyclotron waves. We find two significant differences from the cold-plasma approximation: (1) waves can be excited inside the stop bands and at ion gyrofrequencies for relatively small wave numbers k < Omega(p)/nu(A) and (2) short wavelengths with k > Omega(p)/nu(A) experience strong cyclotron damping. We show that, in general, minimum resonant energy of electrons E-min depends only on the wave number k, magnetic field strength B, and plasma mass density rho and depends on the wave frequency omega only implicitly, via the dispersion relation. Formulae for E-min as function of omega based on cold-plasma approximation predict the lowest energy loss where w -> Omega(+)(He), since in this approximation k -> infinity at these frequencies. We show this inference is incorrect and that kinetic effects mean that the ion gyrofrequencies are no longer necessarily preferential for low energy loss. The lowest values of E-min are obtained where the dispersion supports the largest wave numbers k and in the regions of the largest mass densities rho and the lowest magnetic fields B. For realistic magnetospheric conditions E-min similar to 2 MeV and can only drop to similar to 500 keV inside dense plasmaspheric plumes, with plasma density of the order of 500 cm(-3), or during plasmaspheric expansions to high L shells (L similar to 7).