Electrostatic broadband ELF wave emission by Alfven wave breaking

The linear and nonlinear kinetic properties of electrostatic oblique waves below the lower hybrid frequency are investigated. For propagation angles l = k(parallel to)/k(perpendicular to) < root m(e)/m(i) the waves are damped by either parallel electron Landau or ion cyclotron damping. For T-i/T-e much greater than 1 the waves are only weakly damped and can propagate. These waves are called slow ion cyclotron (SIG) and slow ion acoustic (SIA) waves. A fluid-kinetic model, comprised of hot linear kinetic ions and cold nonlinear fluid electrons, is proposed to describe a nonlinear wave breaking process of small-scale Alfven waves resulting in broadband extremely low-frequency (ELF) wave emission. Numerical solutions of the fluid-kinetic model are compared to the electric and magnetic fields of solitary kinetic Alfven waves and broadband ELF waves observed by the Freja satellite within a hot ion environment. The agreement in waveform morphology and amplitude between the fluid-kinetic simulations and the observed waves provides support for the theory that observed SIA waves are the result of a nonlinear emission process from SIC waves.