Nightside Auroral Arcs Near the Electron Isotropy Boundary: TRACERS–THEMIS–MetOp Observations

Abstract Particle precipitation is the ultimate driver of aurorae. Monoenergetic (∼keV) electrons accelerated above the ionosphere produce discrete auroral forms and are associated with field‐aligned currents that govern magnetosphere–ionosphere (MI) coupling. These precipitating electrons exhibit complex angular distributions and are often collocated with energetic ( keV) electron precipitation, affecting ionospheric conductance and current closure. Here, we present observations from the recently launched NASA TRACERS mission, resolving the fine energy and angular structure of monoenergetic precipitation. Coordinated observations with MetOp spacecraft and equatorial measurements from the THEMIS mission reveal the associated energetic electron precipitation. The impact of this energetic electron precipitation on current closure is quantified and discussed. We further develop an empirical model for the angular distributions of monoenergetic precipitation, enabling their realistic incorporation into ionospheric models.