On the possibility of beat excitation of whistler sidebands in the magnetosphere via ponderomotive force

Abstract

We propose a new mechanism to explain the observed sidebands of whistler waves. The mechanism based on nonlinear interaction has potential application to active experiments in the magnetosphere. The process requires two whistler waves with nearly equal frequency ω1‐ω2 and forward and backward traveling components. They exert a parallel ponderomotive force on the electrons at the difference frequency (ω1‐ω2). The modulation of the plasma density by the nonlinear mixing of these two waves, in conjunction with the oscillatory electron velocity at ω1 and ω2 generates a nonlinear current. This nonlinear current drives the first‐order sidebands. In the presence of low frequency density modulation, the oscillatory velocities at the first‐order sidebands generate second‐order sidebands. The process continues to generate higher order sidebands. The sidebands up to seventh order have been observed in VLF experiment at Siple station. The mechanism is effective for the large amplitude waves.