Correlated Discontinuous Energetic and Auroral Electron Precipitations in the Polar Cap

We report coordinated observations of structured, discontinuous energetic electron precipitation (EEP) near the outer radiation belt boundary (oRB), using FY-3E particle measurements together with DMSP/SSUSI auroral imaging and DMSP particle data. These events are characterized by latitudinally separated precipitations with nearly isotropic pitch-angle distributions (PAD) for electrons up to tens–hundreds of keV, and spatial coincidence between EEP and localized auroral structures (double ovals, transpolar arcs, structured diffuse aurora, etc.). Two principal scattering pathways for energetic electron precipitations are identified: (a) field-line curvature scattering (FLCS) in the locally stretched plasma sheet (PS), which produces isotropic precipitations poleward of the oRB; and (b) wave-particle interaction (WPI), where whistler waves scatter electrons across a broad energy range. Furthermore, energetic precipitations are likely confined to closed field lines, indicating the closed field line topology for coexisting auroral structures in polar cap regions. In a discrete arc event, the flux-energy profiles of FY electrons are distinct from the monoenergetic auroral electrons, pointing to a scenario involving different electron precipitating mechanisms: localized structures with shear flows in the equatorial plane create curvature conditions for scattering energetic PS electrons, while the shear flow associated field-aligned currents generate parallel potential in the low-altitude aurora zone, accelerating and precipitating auroral electrons. In an overall diffuse event, the diffuse flux-energy profiles extend from auroral to FY energies, suggesting broadband scattering by waves; additional monoenergetic electrons are superposed on the diffuse spectrum, producing discrete auroral filaments on the diffuse background. The observations of discontinuous correlating energetic and auroral electron precipitations reveals the meso-scale magnetosphere-ionosphere coupling along field lines, and such coordinated examinations can potentially serve as a method to study the coupling processes.