Electron Scattering by Highly Oblique Quasi-Electrostatic Chorus Waves Under Realistic Magnetospheric Conditions

Using Van Allen Probes data (2013–2015), we report that highly oblique chorus waves frequently occur in low-density regions where (Formula presented.). These waves exhibit an electric-to-magnetic energy ratio (Formula presented.), much higher than the typical (Formula presented.) for quasi-parallel chorus, indicating a quasi-electrostatic nature, termed highly oblique quasi-electrostatic (HOQE) chorus. Incorporating realistic wave properties and plasma environments, numerical modeling shows that HOQE lower-band chorus with the central wave normal angle (Formula presented.) can efficiently scatter relativistic electrons up to 2 MeV near (Formula presented.) equatorial pitch angles primarily via higher-order resonance. Additionally, HOQE upper-band chorus (Formula presented.) drives strong diffusion of tens of keV electrons at moderate pitch angles. These findings reveal a previously overlooked pathway for MeV electron loss, advancing our understanding of chorus wave-particle interactions.