Simulation Study of Cusp Neutral Density Structuring

Observations of neutral structuring in the cusp has been reported by several satellite and rocket missions. Observations include altitude dependent neutral density enhancements (CHAMP, GRACE) and slight neutral density depletions at lower altitudes (Streak, RENU2). One theorized driver of the neutral enhancement includes processes associated with soft electron precipitation, ion upwelling, and ion-neutral momentum exchange. We investigate these processes as they relate to neutral structuring using a kilometer-scale, three-fluid, ionosphere-thermosphere numerical model which includes inertial ion and neutral terms. Results are presented which illustrate details of the underlying physics driving the neutral structuring from these processes. Ion-neutral coupling is found to span vertically for hundreds of kilometers for 15-20 minutes, enhancing neural density. New results are presented which suggest a mechanism for the observed neutral density depletions.