Low-Altitude Observations of Recurrent Short-Lived keV Ion Micro-Injections Inside the Diffuse Auroral Zone

Abstract : The AMBRE experiment onboard the ocean topography mapper JASON‐3 aims at measuring the spacecraft potential as well as auroral particle precipitation using two top‐hat analyzers for electrons and ions in the 20 eV‐28 keV energy range. The JASON‐3 spacecraft has a nearly circular orbit at an altitude of 1336 km with an inclination of 66°, at times probing the equatorward part of the auroral oval in a nearly tangential manner upon leaving the outer radiation belt. In this region of space, during periods of enhanced geomagnetic activity with small or moderate storms, AMBRE detected recurrent “micro‐injections” of ions with energies in the 200 eV‐28 keV range and which exhibit clear time of flight dispersion. Ray tracing using single trajectory computations suggests that these ions are launched from a source located in the 8000‐12000 km altitudinal range and subsequently propagate downward toward the ionosphere. Such observations of quasi‐periodic dispersed downflowing ions are new and we argue that these structures could be produced by ion‐wave interactions at mid‐altitudes.