Journal Article

Giant Undulations Driven by Pitch‐Angle Scattering of Time Domain Structures Modulated by Plasmapause Surface Wave

Du, Pei‐Heng, Shi, Quan‐Qi, Guo, Meng‐Dan, Zhang, Yong‐Liang, Rong, Zhaojin, Yao, Zhong‐Hua, Wei, Yong, Liu, Jian, Zhong, Jun, Zhang, Xiao‐Xin, Zhou, Yi‐Jia, He, Fei

2025

Overview

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 electron precipitation via modulating the time domain structures rather than the previously predicted chorus or electron cyclotron harmonic waves. Plain Language Summary Boundary surface waves usually act as a kind of special oscillation along the boundary layer and are the widely existing physical phenomena in the universe. In our Earth, there are magnetopause surface wave and plasmapause surface wave. For the latter, the plasmapause surface wave has been confirmed to be a kind of sawtooth‐type auroral structures locating on the equatorial edge of aurora oval, named as giant undulations. But how can the plasmapause surface wave produce the auroral giant undulations is still unknown. Based on this question, we have provided the observational evidence of auroral giant undulations being driven by the periodic pitch‐angle scattering of time domain structures modulated by plasmapause surface waves. Our new results in this research would help us to better understand the energy conversion controlled by boundary dynamics and the crucial effect of boundary dynamics on the near‐surface space environment. Key Points Giant undulations (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 Total fluxes during one plasmapause surface wave (PSW) period and energy of scattered electron and ions determine the size and luminosity of GUs PSWs can cause periodic electron precipitation by modulating time domain structures

• Publisher: John Wiley & Sons, Inc,American Geophysical Union (AGU),Wiley
• Subject: Aerospace environments / Auroras / Boundary layers / Cyclotrons / Diffuse aurora / Earth magnetosphere / Electron oscillations / Electron precipitation / Electrons / Energy / Energy conversion / giant undulations / Ions / Luminosity / Magnetopause / Particle interactions / Physical phenomena / Pitch (inclination) / pitch angle / Plasmapause / plasmapause surface wave / Scattering / Structures / Surface water waves / Surface waves / Time domain analysis / Waves