Electron Scattering by Plasmaspheric Hiss in a Nightside Plume

Abstract

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.

Quantification of Energetic Electron Precipitation Driven by Plume Whistler Mode Waves, Plasmaspheric Hiss, and Exohiss

“…Plasmaspheric plumes are found to be favorable for enhancing pitch angle scattering of radiation belt electrons, thus leading to electron precipitation into the upper atmosphere (Borovsky et al, 2014;Summers et al, 2008;Zhang et al, 2018). Borovsky and Steinberg (2006) found that relativistic electron dropouts at geosynchronous orbit often coincided with the presence of plasmaspheric plumes, suggesting the potential loss of energetic electrons due to interactions with the enhanced plasma waves in plumes.…”

Statistical Properties of Hiss in Plasmaspheric Plumes and Associated Scattering Losses of Radiation Belt Electrons

“…We further assume that the initial electron PSD follows a sinusoidal function of equatorial pitch angle. We define the electron loss timescale ( τ D ) as the exponential decay timescale after the approach of electron equilibrium state and then follow the studies of Ni et al () and Zhang et al () to calculate τ D as …”

“…Radiation belt electrons can be affected by various magnetospheric wave modes, including whistler mode chorus, plasmaspheric hiss, magnetosonic waves, electromagnetic ion cyclotron waves, and electrostatic electron cyclotron harmonic waves, via wave-particle interaction processes (e.g., Ni et al, 2016;Shprits et al, 2008;Summers et al, 2007;Thorne, 2010), and ultralow frequency wave-driven diffusion (e.g., Su, Zhu, Xiao, Zong, et al, 2015). Among these waves, hiss is typically regarded as a structureless, broadband whistler mode emission naturally occurring inside the plasmasphere (e.g., Meredith et al, 2004;Thorne et al, 1973), high-density plasmaspheric plumes (e.g., Summers et al, 2008;Zhang et al, 2018), and lowdensity plasmatrough (Hua et al, 2018;Su et al, 2018a;Zhu et al, 2015). A few recent studies reported hiss emissions with short-time (tens of milliseconds) rising and falling tones (Summers et al, 2014), long-lasting (~1 s) rising tones, and large amplitude (up to 1.5 nT) hiss waveforms in the plasmaspheric plumes (Su et al, 2018b).…”

Low Frequency (f < 200 Hz) Polar Plasmaspheric Hiss: Coherent and Intense

“…Circulation models cannot be applied for such small regions of space. Recent works on hiss within plumes (Hartley et al, 2019;Li et al, 2019;Nakamura et al, 2018;Shi et al, 2019;Teng et al, 2019;Zhang et al, 2018), although not the main focus of this paper, will be commented on in sections 4 and 5 of this paper in this light.…”