Bounce Resonance Scattering of Radiation Belt Electrons by Low‐Frequency Hiss: Comparison With Cyclotron and Landau Resonances

Abstract

AbstractBounce resonant interactions with magnetospheric waves have been proposed as an important contributing mechanism for scattering near‐equatorially mirroring electrons by violating the second adiabatic invariant associated with the electron bounce motion along a geomagnetic field line. This study demonstrates that low‐frequency plasmaspheric hiss with significant wave power below 100 Hz can bounce resonate efficiently with radiation belt electrons. By performing quantitative calculations of pitch angle scattering rates, we show that low‐frequency hiss‐induced bounce resonant scattering of electrons has a strong dependence on equatorial pitch angle αeq. For electrons with αeq close to 90°, the timescale associated with bounce resonance scattering can be comparable to or even less than 1 h. Cyclotron and Landau resonant interactions between low‐frequency hiss and electrons are also investigated for comparisons. It is found that while the bounce and Landau resonances are responsible for the diffusive transport of near‐equatorially mirroring electrons to lower αeq, pitch angle scattering by cyclotron resonance could take over to further diffuse electrons into the atmosphere. Bounce resonance provides a more efficient pitch angle scattering mechanism of relativistic (≥1 MeV) electrons than Landau resonance due to the stronger scattering rates and broader resonance coverage of αeq, thereby demonstrating that bounce resonance scattering by low‐frequency hiss can contribute importantly to the evolution of the electron pitch angle distribution and the loss of radiation belt electrons.