First simultaneous measurements of Na and K thermospheric layers along with TILs from Arecibo

This work presents the first simultaneous observations of Na and K between 120 and 150 km altitudes along with ionospheric tidal ion layers (TILs) obtained on 30 January 2006 data from Arecibo. The latter displays an average downward phase velocity of ∼14.7 ms^-1. However, the neutral layers descend together at a much slower velocity of about ∼0.69 ms^-1. This indicates that thermospheric atomic metal layers are not necessarily associated with TILs. The ratio of the average Na/K abundances in thermosphere is ∼35.5 as compared to 150 in the main layer (80-105 km). The long lifetimes of ions at ∼140 km implies that neutral layers cannot result from direct neutralization of metal ions in the TILs. We investigate different mechanisms that can deposit neutral atoms at thermospheric altitudes.