Studies of atmospheric gravity waves in the mesopause region using airglow imaging.

摘要

Atmospheric gravity waves play a significant role in the dynamics and thermal balance in the mesopause region. In this thesis, an automated and robust processing and analysis scheme has been developed to detect and estimate high-frequency quasi-monochromatic wave components from airglow image sequences and associated background wind measurements. The two-dimensional cross-periodogram of two Doppler-shifted time-differenced airglow images is utilized to extract intrinsic wave parameters. The momentum fluxes of observed vertically propagating wave components are estimated using an analytical model relating momentum flux to the extracted wave parameters. This newly developed scheme enables characterization of variations in the propagation direction and strength of gravity waves with high temporal resolution. More significantly, it provides an objective and feasible approach to draw statistical information for investigating seasonal and geographical variations in momentum flux of gravity waves.; Observational investigations of gravity wave momentum flux have been performed at Starfire Optical Range, New Mexico (35°N, 107°W) and Maui, Hawaii (20.7°N, 156.3°W). Using the existing and newly developed techniques, seasonal variations in gravity wave momentum flux at these two locations are estimated from hydroxyl (OH) airglow imaging data together with lidar/radar wind measurements. The average wave propagation directions at both locations have a common seasonal preference, which is southwestward in winter and northeastward in summer. When combined with results from other studies, these results support the notion that the seasonal trend in meridional flux, which is equatorward in winter and poleward in summer, is a widespread phenomenon.; To explore the potential of studying wave propagation through airglow layers using imaging systems, numerical simulations have been carried out to retrieve vertical structures from multisensor imaging measurements. Regularization techniques have been compared in the tomographic reconstruction processes of retrieving synthetic wave structures. Various combinations of number and separation of imagers are considered for showing the effect of system geometry on the reconstruction performance. Further studies on optimal configuration of imaging systems will provide essential guidance to design experiments for investigating vertical properties of gravity waves such as wave damping and breaking phenomena.