Observations of ion layer motions during the AIDA campaign

The AIDA-89 campaign has yielded the most comprehensive set of low-latitude incoherent scatter radar power profiles and derived electron concentration results ever made. These results have been used to study the time-height trajectories of 80-150 km ion layers and serve to gauge both the periodicity and variability of ion layer structure throughout the campaign. Features of the AIDA ion layer trajectories point to a dynamics 'zoo' of processes ranging from multiday-period waves, tides and acoustic-gravity waves (AGWs) to geomagnetic storm effects and evidence of coupled neutral sodium and ion layer/plasma processes. The semidiurnal and diurnal tides are evidenced in the almost always present layers, the Tidal Ion Layers (TILs), which are identified by their regular and periodic trajectories that also display regions of variable mixing or confluence of the various tides. The TILs are contrasted with the truly sporadic layers that include sporadic E and sporadic intermediate layers. The sporadic layers may be formed due to interaction of the tidal wind system with AGWs. The formation process may involve horizontal as well as vertical ion convergence mechanisms and/or various non-linear effects. Limits to the study derive from volume undersampling due to use of the single radar beam.