Excitation of electrostatic nonlinear structures associated with whistler-mode chorus waves

The simultaneous observations of Langmuir waves in association with whistler-mode chorus and its harmonics in both the Earth's inner magnetosphere and magnetopause boundary layer raise the question how these high frequency waves are generated. The observed modulation of Langmuir waves by chorus wave phase suggests that the energy is possibly channeled from chorus into Langmuir waves. Using particle-in-cell simulations, we explore how a spatially modulated beam is formed by the shallowly trapped electrons in the potential well of chorus which excites Langmuir waves. We demonstrate that the harmonics of chorus are a manifestation of the phase bunching of trapped electrons.