Dr. Lunjin Chen
University of California Los Angeles
Plasmaspheric hiss (PH) is an incoherent electromagnetic noise in the frequency range between ~ 200 Hz and 2 kHz that naturally occurs inside the plasmasphere, a torus region of relatively dense (~10s-1000s cm-3) and cool (~ 1 eV, equivalent to ~11,000 kelvin) ionized gas from about 1.5 to 7 Earth radii above the Earth's surface. PH has long been known to be responsible for the scattering of energetic electrons into loss cone of the Earth's dipolar magnetic field via wave-particle resonant interaction and thus for the formation of two-zone structures of radiation belts, a population of trapped relativistic electrons (> 100 keV) over spatial region similar to the plasmasphere. Despite its importance, the origin of PH has been debated for decades since its discovery in 1960s. The mechanisms of PH generation will be reviewed. Increasing observational evidence and recent ray tracing simulation have supported that PH emission originates from another electromagnetic emission, chorus emission, which is excited outside the plasmasphere. The chorus as embryonic source is able to reproduce many important characteristics of PH observation, including the observed frequency spectrum, spatial confinement inside the plasmasphere, and modulation of hiss intensity by the ambient plasma density variations. At the end, the future work will be discussed on addressing other unresolved PH-related science questions through the newly launched NASA Radiation Belt Storm Probes mission.
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