The Principal Role of Chorus Ducting for Night‐Side Relativistic Electron Precipitation

Abstract Night‐side chorus waves are often observed during plasma sheet injections, typically confined around the equator and thus potentially responsible for precipitation of ≲100 keV electrons. However, recent low‐altitude observations have revealed the critical role of chorus waves in scattering relativistic electrons on the night‐side. This study presents a night‐side relativistic electron precipitation event induced by chorus waves at the strong diffusion regime, as observed by the ELFIN CubeSats. Through event‐based modeling of wave propagation under ducted or unducted regimes, we show that a density duct is essential for guiding chorus waves to high latitudes with minimal damping, thus enabling the strong night‐side relativistic electron precipitation. These findings underline both the existence and the important role of density ducts in facilitating night‐side relativistic electron precipitation.