Abstract

The Ion Velocity Meter instrument on the Ionospheric Connection Explorer (ICON) satellite measured large depletions in the O+ density (but not H+) in the post-midnight topside ionosphere on December 23, 2019. This phenomenon has been observed previously but has yet to be explained. The authors pr... Show moreThe Ion Velocity Meter instrument on the Ionospheric Connection Explorer (ICON) satellite measured large depletions in the O+ density (but not H+) in the post-midnight topside ionosphere on December 23, 2019. This phenomenon has been observed previously but has yet to be explained. The authors provide for the first time a physical explanation for this observation based on a simulation study using the first-principles, ionosphere/plasmasphere code SAMI3 (Sami3 is also a model of the ionosphere) with neutral atmosphere inputs (neutral wind, density, and temperature) from the whole atmosphere model Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (WACCM-X). The physical processes responsible for these observations are (1) the nighttime O+/H+ transition altitude is below the ICON orbit and (2) a prolonged downward E x B drift in the post-midnight/pre-sunrise time sector. Interestingly, the authors also find that equatorial plasma bubbles develop in the African and Pacific sectors. Show less