General theory of the alkali metals present in the earth's upper atmosphere. III - Diurnal variations

Abstract : As a final test of the flux model described in the first paper and already used to retrieve the meridional and seasonal variations of the different alkalis, the diurnal variation of the sodium layer is simulated and compared to recently obtained lidar data. The relative importance of neutral and ionic processes on short time scales are discussed for various conditions corresponding to daytime, sunset nighttime and sunrise, and for various altitude levels. It is thus shown that the ionic compounds, which play an important role on the long term behavior of the sodium layer, have only a slight influence on its variation during a diurnal cycle. A theoretical explanation of the lack of variation of the sodium total abundance larger than + or - 10 percent is obtained.