Observations and theory of ion gyro-harmonic structures in the stimulated radiation spectrum during second electron gyro-harmonic heating

Recent observations of Stimulated Electromagnetic Emissions SEE for ionospheric heating near the second electron gyro-harmonic frequency at the HAARP facility are provided. These observations show previously unobserved structures ordered by harmonics of the ion gyro-frequency. An analytical model is presented for three-wave coupling between the pump wave, upper hybrid/electron Bernstein waves, and electrostatic ion cyclotron harmonic waves. It is shown that for pump wave frequencies near the second electron gyro-harmonic, a band of upper hybrid/electron Bernstein waves separated by harmonics of the ion gyro-frequency can be destabilized. A new 2-D computational model using the Particle-In-Cell PIC method is used to more thoroughly investigate the nonlinear processes involved in producing these spectral features and provide results reasonably in line with predictions of the simplified analytical model.