April 14, 2017, 1:00 pm - 2:00 pm

April 14, 1:00 pm - 2:00 pm

Nonlinear evolution of oblique whistler waves

Kyunghwan Dokgo (Korea Advanced Institute of Science and Technology)

Whistler waves are ubiquitously observed in space and laboratory plasmas. In particular, they are thought to play a major role in accelerations and losses of relativistic electrons in the terrestrial radiation belts. Recently, in-situ observations show that a significant fraction of large amplitude whistler waves propagate in the direction oblique to the background magnetic field.

Here we present nonlinear evolutions of oblique whistler waves using 1-D Particle-In-Cell (PIC) code. Notable features include the generation of whistler harmonics and their nonlinear evolution via Landau damping. Additionally, using test particles, we demonstrate that the whistler harmonics are generated by the coherence of longitudinal particle motions. Such particle motions lead the longitudinal current and electric field to develop, eventually triggering whistler harmonics. The power of harmonics become larger when particles are trapped by the electric potential. In general, whistler waves are damped by the O'Neil-type damping while the stochastic interaction drives Landau-type damping. The ratio between the frequency associated with particle trapping and the relevant particle's gyro frequency play an important role in determining the coherent vs. incoherent interaction. This study provides detailed microphysical contexts for the generation and evolution of whistler waves observed in geospace.