ELECTROSTATIC BROAD-BAND ELF WAVE EMISSION BY ALFVEN-WAVE BREAKING

The linear and nonlinear kinetic properties of electrostatic oblique w aves below the lower hybrid frequency are investigated. For propagatio n angles l = k(parallel to)/k(perpendicular to) < root m(e)/m(i) the w aves are damped by either parallel electron Landau or ion cyclotron da mping. For T-i/T-e much greater than 1 the waves are only weakly dampe d and can propagate. These waves are called slow ion cyclotron (SIG) a nd slow ion acoustic (SIA) waves. A fluid-kinetic model, comprised of hot linear kinetic ions and cold nonlinear fluid electrons, is propose d to describe a nonlinear wave breaking process of small-scale Alfven waves resulting in broadband extremely low-frequency (ELF) wave emissi on. Numerical solutions of the fluid-kinetic model are compared to the electric and magnetic fields of solitary kinetic Alfven waves and bro adband ELF waves observed by the Freja satellite within a hot ion envi ronment. The agreement in waveform morphology and amplitude between th e fluid-kinetic simulations and the observed waves provides support fo r the theory that observed SIA waves are the result of a nonlinear emi ssion process from SIC waves.