Electrostatic broadband ELF wave

The linear and nonlinear kinetic properties of electrostatic oblique waves below the lower hybrid frequency are investigated. For propagation angles # = k k =k ? < q m e =m i the waves are damped by either parallel electron Landau or ion cyclotron damping. For T i =T e 1 the waves are only weakly damped and can propagate. These waves are called slow ion cyclotron (SIC) and slow ion acoustic (SIA) waves. A uid-kinetic model, comprised of hot linear kinetic ions and cold nonlinear uid electrons, is proposed to describe a nonlinear wave breaking process of small-scale Alfv en waves resulting in broadband extremely low-frequency (ELF) wave emission. Numerical solutions of the uid-kinetic model are compared to the electric and magnetic elds of solitary kinetic Alfv en waves and broadband ELF waves observed by the Freja satellite within a hot ion environment. The agreement in waveform morphology and amplitude between the uid-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.