Didebulidze, G., Gudadze, N., Lomidze, L. and Javakhishvili, G.
Georgian National Astrophysical Observatory (former Abastumani Astrophysical Observatory), Tbilisi, Georgia
The long-term variations in the ionosphere F2 layer peak height (hmF2) for day- and night-time conditions and for different seasons is investigated using Tbilisi (41.65 N, 44.75 E) ionosonde data obtained in 1963-1986. The revealed lowering of hmF2 is compared with the oxygen red 630.0 nm line total nightglow intensity seasonal and night long-term variations at Abastumani (41.75 N; 42.82 E) in 1957-1993. The long-term increase in the 630.0 nm intensity observed after astronomical twilight for most seasons and its decrease during midnight is considered as a result of the lowering of the ionosphere hmF2 peak height. The different values of the red line intensity long-term change (increasing trend after twilight and decreasing at midnight) in different seasons may result from the meridional wind velocity long-term changes. By using a simple Chapman type (damping in time) layer for the ionosphere F2 region electron density height distribution, which takes into account a meridional wind velocity, an estimation of the lowering of the ionosphere peak height for any month and corresponding red line intensity nighttime behaviour is done.