LAUSR

Second harmonics have been observed in various magnetospheric waves. Although particle simulations are able to produce the similar features as reported in satellite observations, the exact physical mechanism for the generation of second harmonics remains uncovered yet. In this letter, we first give wave equations describing the fundamental and second harmonics via multiscale analysis. Then, we apply a kinetic theory approach to obtain the conductivity tensor, nonlinear current density, and the necessary conditions for the second harmonic generation of electromagnetic emissions in a magnetized plasma. To verify our theoretical results, we also perform hybrid simulations to study the second harmonic generation of electromagnetic ion cyclotron waves for three cases in which the second harmonic deviates from the inherent modes by different degrees. Our results suggest the important role of the linear dispersion relation in the second‐harmonic generation.