On the possibility of in situ shear excitation of vortical perturbations and their coupling with short-period gravity waves by airglow and ionosphere observations

Abstract

The essential part of in situ shear excited vortical perturbations (shear waves) at mesosphere–thermosphere heights is considered by use of airglow, from Abastumani (42.8°E, 41.8°N), and ionospheric, from Tbilisi (44.8°E 41.7°N), observations. One of the characteristic processes for excitation of vortical perturbations (shear waves) is a phenomenon of its possible transformation into short-period atmospheric gravity waves (GWs) with a frequency close to the Brunt–Väisälä frequency (BVf). More convenient condition for shear excitation of vortical perturbations and their transformation into short-period GWs at mesosphere–thermosphere heights appears on magnetically disturbed days and during the mid-latitude springtime transition. Nighttime observations of intensities of the hydroxyl OH(8-3) band, the oxygen green 557.7 and red 630.0 nm lines from Abastumani show a possible presence of shear excited vortical perturbations and an accumulation of wave energy by short-period GWs with frequencies close to BVf on magnetically disturbed days and during springtime transition. The amplitude amplification of short-period gravity waves is considered as a possible indicator of regional and planetary scale changes of the horizontal wind in the upper atmosphere.