Airglow variations and dynamics in the lower thermosphere and upper mesosphere—1. Diurnal variation and its seasonal dependency

Abstract

An attempt was made to examine the relationship of the diurnal variations of the 5577 Å[OI], NaD and OH-band airglow emissions with the upper atmospheric dynamics. A structure function analysis was made to find predominant periods of the variations of the emission intensities. The results show the presence of a prevailing semidiurnal variation in the 5577 Å intensity at middle latitudes. Characteristics of the seasonal dependency in both amplitude and phase of this semidiurnal oscillation, computed by the method of least square, are extremely in good agreement with those of the solar semidiurnal tidal wind in the meteor region. This suggests that the solar semidiurnal tide may be the main cause for the diurnal variation of the 5577 Å emission at middle latitudes. The diurnal variations of the NaD, OH-band and 5577 Å emissions are discussed, in relation to the dynamical characteristics of the solar tidal waves around the base of the thermosphere.