Observations of ion and sodium layer coupled processes during AIDA

Extended measurements of the neutral sodium layer using lidar and of the lower ionosphere using Incoherent Scatter Radar were conducted at Arecibo during the spring 1989 AIDA campaign. We present results from four nights of these rather extensive, almost common volume, simultaneous observations of the 80-110 km altitude region. Although in each set of results there are unique features that appear to be associated with the diverse dynamics of the atmosphere, the general nocturnal motion of both the sodium and ion layers is controlled by the tidal wind. Additionally, there is often a very strong correlation between the presence of narrow ionization and narrow sodium layers below 100 km altitude. These sporadic E and sporadic sodium layers usually occur at the same heights and with a sometimes striking correspondence in the details of vertical and temporal structure. These details are seen most clearly in a series of time-height plots of sodium concentration over which are overlaid the corresponding time-height trajectories of the ionization layers. Included in this series of plots are the two most spectacular of the layering events observed during AIDA. The most intense of the events occurred on the night of 30-31 March and was characterized by ion and sodium layers, with about 6 km vertical extent, that formed near 95 km altitude. During this event the sodium column content was observed to increase by a factor of about 10, from 1.5-2.0 × 10⁹ to 20 × 10⁹ cm ², in 90 min. The second of the major events occurred on the night of 5-6 April and was characterized by a strong vertical oscillation of the sodium layer with a peak-to-peak amplitude of 2-3 km and a period of 10.4 min. For contrast with the two major events and because of the completeness of the data sets, results from the nights of 4-5 April and 7-8 April are also given.