Nonlinear VLF effects in the topside ionosphere

The Demeter satellite observed intense broadband lower‐ and upper‐hybrid electrostatic waves and plasma perturbations associated with high‐power whistler‐mode signals from the very‐low frequency (VLF) transmitter NWC. This paper shows that the Demeter observations can be explained by nonlinear interactions driven by VLF pump waves, thereby suggesting that nonlinear effects are responsible for energy losses of high‐power VLF signals in the ionosphere.