Combined Scattering of Radiation Belt Electrons by Low‐Frequency Hiss: Cyclotron, Landau, and Bounce Resonances

Abstract

Low‐frequency hiss is known to play an important role in the precipitation of radiation belt electrons by cyclotron, Landau, and bounce resonances. To investigate the potential combined scattering effect caused by these resonant processes, we analyze the resonant conditions and develop a full relativistic test particle code to quantify the net pitch angle scattering efficiency. It is indicated that the three resonance processes can coexist to scatter electrons at different energies and pitch angles, with the net pitch angle scattering rates up to ~10−3 s−1 for low‐frequency hiss ~175 pT at L = 4.5. Comparisons with the quasi‐linear theory results demonstrate that the cyclotron resonance is mainly responsible for the pitch angle scattering of electrons < ~ 80°, while both Landau and bounce resonances can affect the scattering of near‐equatorially mirroring electrons and their combined diffusion produces smaller scattering coefficients compared to quasi‐linear theory calculations.

Statistical Characteristics of Electron Pitch Angle Distributions Inside the Magnetopasue Based on MMS Observations

“…Substorm injected electrons are almost isotropic (Åsnes et al, 2005). The isotropy distribution could also result from pitch angle scattering by whistler waves at the separatrix (Fu et al, 2012; Z. Wang et al, 2019); (5) cigar distribution (also named as bidirectional PAD) with a maximum flux around α = 0° or/and 180° but a minimum at large α (Fu et al, 2011; Fu, Yi, et al, 2020; Huang et al, 2020; Liu, Fu, Xu, Cao, & Liu, 2017; Ni et al, 2020; Zhou et al, 2019); it is probably a result of Fermi acceleration contributed by the compression of magnetic field line (Angelopoulos & Fu, 2016); (6) rolling‐pin distribution with electron fluxes mainly at α = 0°, 90°, and 180° (Fu, Zhao, et al, 2020; Liu, Fu, Xu, Wang, et al, 2017; M. J. Zhao, Fu, et al, 2019) that is due to both global‐scale Fermi acceleration and local‐scale betatron acceleration (Liu, Fu, Xu, Wang, et al, 2017).…”

Parametric Dependence of the Formation of Electron Butterfly Pitch Angle Distribution Driven by Magnetosonic Waves

“…Following the previous TP simulations (e.g., Fu et al, 2019, 2020; K. Liu et al, 2010, 2012; Tao et al, 2011, 2012), the motion of charged particles impacted by plasma waves in the Earth magnetic field is described by the full relativistic Lorentz equation , where m and q are the rest mass and charge of a relativistic electron, respectively; v is the velocity of the electron; is the Lorentz factor; c is the speed of light in vacuum; B 0 represents the background magnetic field; and B w and E w are the magnetic field and electric field of the MS waves, respectively. Here we adopt the Boris method (Boris, 1970) to numerically solve the relativistic Lorentz equation.…”

Empirical Loss Timescales of Slot Region Electrons due to Plasmaspheric Hiss Based on Van Allen Probes Observations

“…Plasmaspheric hiss plays a crucial role in the dynamics and overall structure of the Earths' radiation belts (e.g., Cao et al., 2017; Claudepierre et al., 2020; Mourenas et al., 2017; Ni et al., 2013; Summers et al., 2007b, 2007a; Thorne, 2010). Plasmaspheric hiss can cause the precipitation loss of energetic and relativistic radiation belt electrons through pitch angle scattering (e.g., Cao et al., 2020; Fu et al., 2020; Hua et al., 2018; Meredith et al., 2009; Ni et al., 2019; Orlova et al., 2016; Summers et al., 2008; Zhao et al., 2019). Hiss wave driven electron loss has been recognized to be primarily responsible for the formation of slot region (∼2 < L < 3) which separates the Earth's inner and outer radiation belts, although losses due to LGWs and Very Low Frequency (VLF) transmitters may be important at lower energies (e.g., Abel & Thorne, 1998; Rodger & Clilverd, 2002; Ross et al., 2019; Voss et al., 1998).…”