Giant Undulations driven by Pitch-Angle Scattering of Time Domain Structures modulated by Plasmapause Surface Wave

Plasmapause surface waves (PSWs) near the plasmapause boundary are regarded to be the magnetospheric source of ionospheric auroral giant undulations (GUs) located at the equatorward boundary of diffuse aurora. However, the observational evidence of wave-particle interaction connecting PSWs and GUs is absent. In this letter, we demonstrate GUs are driven by pitch-angle scattering of time domain structures modulated by the PSWs, based on the conjugated ionospheric and magnetospheric observations. Specifically, ionospheric GUs are lighted by the pitch-angle scattering of < 1 keV thermal electron and ions and energetic ions with energy up to dozens of keV near the plasmapause. Further, the total fluxes during one PSW period and energy of scattered electron and ions determine the size and luminosity of GUs. Our research provides observational evidence that PSWs cause periodic particle precipitation via modulating the time domain structures rather than the previously predicted chorus or electron cyclotron harmonic (ECH) waves.