Whistler mode hiss acts as an important loss mechanism contributing to the radiation belt electron dynamics inside the plasmasphere and plasmaspheric plumes. Based on Van Allen Probes observations from September 2012 to December 2015, we conduct a detailed analysis of hiss properties in plasmaspheric plumes and illustrate that corresponding to the highest occurrence probability of plumes at L = 5.0–6.0 and MLT = 18–21, hiss emissions occur concurrently with a rate of >~80%. Plume hiss can efficiently scatter ~10‐ to 100‐keV electrons at rates up to ~10−4 s−1 near the loss cone, and the resultant electron loss timescales vary largely with energy, that is, from less than an hour for tens of kiloelectron volt electrons to several days for hundreds of kiloelectron volt electrons and to >100 days for >5‐MeV electrons. These newly obtained statistical properties of plume hiss and associated electron scattering effects are useful to future modeling efforts of radiation belt electron dynamics.

Electromagnetic ion cyclotron waves have long been recognized to play a crucial role in the dynamic loss of ring current protons. While the field‐aligned propagation approximation of electromagnetic ion cyclotron waves was widely used to quantify the scattering loss of ring current protons, in this study, we find that the wave normal distribution strongly affects the pitch angle scattering efficiency of protons. Increase of peak normal angle or angular width can considerably reduce the scattering rates of ≤10 keV protons. For >10 keV protons, the field‐aligned propagation approximation results in a pronounced underestimate of the scattering of intermediate equatorial pitch angle protons and overestimates the scattering of high equatorial pitch angle protons by orders of magnitude. Our results suggest that the wave normal distribution of electromagnetic ion cyclotron waves plays an important role in the pitch angle evolution and scattering loss of ring current protons and should be incorporated in future global modeling of ring current dynamics.

In this article, a new technique is proposed which can handle the singularity problem arising in the MoM solution of the electric field integral equation. The method involves MCI technique in evaluation of the moment matrix elements. One major advantage of the MCI technique is that it removes the singularity problem arising in integration of singular integrand without any analytical modification or approximation to the integrand by only employing the "local correction technique," where the uniformly distributed random points are avoided from falling in the vicinity of the observation points. The technique is applied to the problem of scattering from metallic structures for three different test cases showing the local correction for the singular points in each case. It is evident that this new technique is capable of handling the singularity problem very efficiently and easily. ACKNOWLEDGMENT

Scattering by plasmaspheric hiss is responsible for the newly reported reversed energy spectra with abundant high‐energy but fewer low‐energy electrons between hundreds of kiloelectronvolts and ~2 MeV in the inner magnetosphere. To deepen our understanding of the contributions of plasmaspheric hiss to the formation of reversed electron energy spectrum, we conduct a detailed theoretical parametric analysis through numerical simulations to explore the sensitivity of hiss‐induced reversed electron energy spectrum to ambient magnetic field, plasma density, and hiss wave distribution properties. Given L‐shell, variations of ambient plasma density and wave frequency spectrum contribute importantly to the formation of reversed electron energy spectrum, while variations of background magnetic field (which usually shows small changes in the plasmasphere) and wave normal angle distribution play a less effective role. Our study suggests that the reversed electron energy spectrum has important implications for unveiling the sophisticated energy‐dependent nature of wave‐particle interactions and energetic particle dynamics in geospace.

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Strong electrostatic electron cyclotron harmonic (ECH) waves on the dayside magnetosphere have been reported based on observations of the Magnetospheric Multiscale (MMS) spacecraft. In this study, we analyze high‐quality wave data from the four MMS satellites between 1 September 2015 and 30 August 2018 to investigate the statistical properties of dayside ECH emissions. The results show that dayside ECH waves are preferentially observed on the prenoon side in the outer magnetosphere (L = 8–12), with average wave amplitude Ew > 0.1 mV/m. In addition, besides the typical near‐equatorial (|MLAT| ≤ 15°) region, dayside ECH waves exhibit moderate occurrence rate and wave amplitude in higher latitudinal regions (i.e., 15 < |MLAT| ≤ 40°), possibly due to the off‐equatorial geomagnetic field minimum. Our reported double peaks of dayside ECH wave occurrence zone and considerable occurrence rates of prenoonside ECH waves suggest that dayside ECH waves can be a potentially important contributor to the formation of dayside diffuse aurora.

Bounce 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.

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