Electron Scattering by Plasmaspheric Hiss in a Nightside Plume

Plasmaspheric hiss is known to play an important role in radiation belt electron dynamics in high plasma density regions. We present observations of two crossings of a plasmaspheric plume by the Van Allen Probes on 26 December 2012, which occurred unusually at the post‐midnight‐to‐dawn sector between L ~ 4–6 during a geomagnetically quiet period. This plume exhibited pronounced electron densities higher than those of the average plume level. Moderate hiss emissions accompanied the two plume crossings with the peak power at about 100 Hz. Quantification of quasi‐linear bounce‐averaged electron scattering rates by hiss in the plume demonstrates that the waves are efficient to pitch angle scatter ~10–100 keV electrons at rates up to ~10−4 s−1 near the loss cone but become gradually insignificant to scatter the higher energy electron population. The resultant timescales of electron loss due to hiss in the nightside plume vary largely with electron kinetic energy over 3 orders of magnitude, that is, from several hours for tens of keV electrons to a few days for hundreds of keV electrons to well above 100 days for >1 MeV electrons. Changing slightly with L‐shell and the multiquartile profile of hiss spectral intensity, these electron loss timescales suggest that hiss emissions in the nightside plume act as a viable candidate for the fast loss of the ≲100 keV electrons and the slow decay of higher energy electrons. Plain Language Summary It is believed that the loss dynamics of radiation belt electrons are coherent with hiss dynamics on spatial scales comparable to the size of the plasmasphere. However, most previous studies focused on the timescale of electron scattering induced by hiss observed in the right plasmasphere. In present work, we first time estimate the electron scattering effect by plasmaspheric hiss in nightside plumes. Key Points Moderately strong hiss emissions can occur to peak at ~100 Hz within the two crossings of a pronounced post‐midnight‐to‐dawn plume Plasmaspheric hiss in the nightside plume is efficient to pitch angle scatter ~10–100 keV electrons With the resultant electron loss timescales varying over 3 orders of magnitude, hiss emissions in the nightside plume can account for the fast loss of ≲100 keV electrons and for the slow decay of higher energy electrons