Topside F-region O+ and H+ drifts inferred from Arecibo ISR long pulse echoes

Simultaneous measurements of the fluxes of O+ and H+ ions are essential for detailed studies of the morphology of ionospheric-protonospheric coupling. The large mass difference between these ions can cause them to drift with different speeds during periods of rapid temperature change, a difference that can be detected and tracked using sensitive incoherent scatter radars such as Arecibo. Past Arecibo observations indicate that H+ and O+ upward drifts can differ by as large as 80 m/s after sunset, however, these measurements based on inverting the phase variation of the backscattered signal ACF at different lags, have not been used extensively at Arecibo and elsewhere. We describe a three-stage fitting procedure utilizing spectral and ACF phase models for multi ion F-region plasmas and its application to Arecibo uncoded long pulse returns to estimate ionospheric composition, temperatures, and line-of-sight (LOS) velocity for all charged species. In particular, the LOS velocities of H+ and O+ are estimated individually for the altitude region extending from 400 to 1000 km over a 63 hours long observation window including events of substantial counter-streaming of the heavy and light ions during the post-sunset and pre-sunrise periods.