Effects of Polarization Reversal on the Pitch Angle Scattering of Radiation Belt Electrons and Ring Current Protons by EMIC Waves

Abstract

In this study, we investigate the effects of polarization reversal of electromagnetic ion cyclotron (EMIC) waves at the crossover frequencies on computations of bounce‐averaged pitch angle diffusion coefficients of radiation belt electrons and ring current protons. We find that inclusion of polarization reversal can cause significant changes of H+ band‐induced particle diffusion coefficients, while scattering by the He+ band is almost unaffected. Our results show that the pure L‐mode approach, which has been widely implemented in previous studies, tends to underestimate the diffusion coefficients of ultrarelativistic (>4 MeV) electrons and overestimate those of 10–50 and >100 keV protons caused by H+ band EMIC waves. Especially for >100 keV protons, the differences in diffusion coefficients can be larger by an order of magnitude. We confirm that the polarization reversal can contribute importantly to the scattering loss of radiation belt electrons and ring current protons by H+ band EMIC waves.

Global Distribution of Reversed Energy Spectra of Ring Current Protons Based on Van Allen Probes Observations

“…There are also two collisionless scattering mechanisms for the ring current decay: wave‐particle interactions and field line curvature (FLC) scattering. The electromagnetic ion cyclotron (EMIC) waves can effectively scatter several keV to hundreds of keV protons into the loss cone due to pitch angle diffusion with a time scale of a few hours (Cao et al., 2020, 2019; Cornwall, 1977; Jordanova et al., 1997; Summers, 2005; Xiao et al., 2011). The field line curvature scattering is of importance for the ring current decay when the field line configuration is stretching (Chen et al., 2019; Ebihara et al., 2011; Sergeev et al., 1993; Yu et al., 2020).…”

Effects of Hot Protons on the Pitch Angle Scattering of Ring Current Protons by EMIC Waves

“…EMIC waves are known to be generated by the cyclotron instability of anisotropic distribution of ∼10–100 keV ring current protons (e.g., Anderson et al., 1996; Chen et al., 2010; Cornwall, 1965; Meredith et al., 2014; Min et al., 2015; Saikin et al., 2015; Wang et al., 2016; Yue et al., 2019; Zhang et al., 2014). Cyclotron resonant interactions with EMIC waves are recognized to be one of the dominant mechanisms accounting for the rapid precipitation loss of radiation belt electrons (e.g., Aseev et al., 2017; Cao et al., 2020; Kersten et al., 2014; Liu et al., 2012, 2010; Meredith et al., 2003; Ni et al., 2015, 2018; Ni, Zhang, & Gu, 2022; Shprits et al., 2008, 2013, 2016, 2017; Summers et al., 2007; Summers & Thorne, 2003; Thorne & Kennel, 1971; Usanova et al., 2014; Zhang et al., 2016) and ring current protons (e.g., Bortnik et al., 2006; Cao et al., 2013, 2017, 2019; Cornwall et al., 1970; Jordanova et al., 2001; Lyons & Thorne, 1972; Ma et al., 2019; Millan & Thorne, 2007; Ni, Hua, et al., 2022; Usanova, 2021; Usanova et al., 2010; Xiao et al., 2011) into the atmosphere. EMIC waves can also heat thermal electrons and heavy ions (He + and O + ; e.g., Horne & Thorne, 1997; Thorne & Horne, 1997; Zhang et al., 2011; Zhu et al., 2021).…”

“…2 of 9 the EMIC wave induced pitch angle diffusion coefficients of relativistic electrons. In addition, Cao et al (2020) and Ma et al (2021) suggest that inclusion of hot electrons will significantly weaken the scattering efficiency of 𝐴𝐴 ≤ 100 keV electrons due to plasmapsheric hiss.…”

Parametric Dependence of Polarization Reversal Effects on the Particle Pitch Angle Scattering by EMIC Waves

“…However, by including the polarization reversal from left‐hand to right‐hand at the crossover frequency in the calculations of bounce‐averaged pitch angle diffusion coefficients, Cao, Ni, Summers, Shprits et al. (2020) proved that the inclusion of polarization reversal can significantly affect the H + band wave‐induced scattering loss of both radiation belt electrons and ring current protons. Especially for >100 keV protons, the differences in diffusion coefficients can be larger than an order of magnitude.…”