Generation of unusually low frequency plasmaspheric hiss

Plasmaspheric hiss is an incoherent, broadband electromagnetic whistler-mode emission, preferentially and steadily observed inside high-density plasmasphere and storm-time plasmaspheric plume [1-2]. The frequency of plasmaspheric hiss typically ranges between ~200 Hz and 2 kHz, with peak wave power in a few 100s Hz. It has been recently proposed [3] that the dominant source of this emission is coherent chorus waves generated outside the plasmasphere. Subsequent ray tracing simulations [4] by tracing million rays of chorus waves reproduced a realistically spatial and spectral distribution of plasmaspheric hiss [Figure 1], showing the spatial confinement of plasmaspheric hiss emission within the plasmapause, and the typical frequency range from 200 Hz and 2 kHz with peak intensity around 500-700 Hz. It is worth pointing out that there is little hiss emission below 200 Hz in the simulation, indicating the chorus-as-embryonic-source mechanism does not work for such low frequency because chorus waves at those frequencies cannot propagate inward into the plasmasphere without substantial attenuations.