Earth's mesosphere and lower thermosphere (MLT) contain thermal and wind structures that can support a large population of ducted waves that are confined to localized regions where conditions support their existence and propagation. Often, waves can travel simultaneously in multiple ducts. Distinctive aspects of these waves are that they may grow to large amplitudes, travel large distances horizontally and induce changes far from their sources. Waves ducted in two ducts simultaneously may carry much greater energy over larger distances than waves confined to a single duct. There is a growing body of evidence that large-amplitude ducted waves are associated with frequent occurrences of extensive changes in the MLT. Ducted waves may affect broader regions of the atmosphere than non-ducted waves since the former may transfer energy horizontally over long distances prior to dissipation. Even weak or partial ducting may cause a significant redistribution of wave energy. Ducted waves provide a mechanism for prolific wave sources such as in low-latitude convective zones. The processes by which waves may attain large amplitudes, transfer energy from distant sources and produce effects in the MLT where the waves become untrapped need to be better understood and better characterized to help improve our understanding of the wave control of the MLT. Such a characterization would be the basis for improved parameterization schemes of wave drag for general circulation models. This investigation is a theoretical study supported by data analysis to address outstanding questions concerning the role of ducted waves in the MLT. The specific objectives are to assess the buildup of wave energy in MLT ducts and the propagation and leakage of energy from ducts under realistic MLT conditions. The study will use theory, numerical modeling, and comparisons to observations of ducted waves from an extensive data base of ducted quasi-monochromatic wave events. Data will be obtained from airglow imagers, lidar and radar from diverse locations (Andes Lidar Observatory, Maui, Adelaide, and Alice Springs) and from the SABER instrument on the TIMED satellite. The research focuses on a largely unexplored mechanism for effecting the global redistribution of wave energy in the mesospheric and lower-thermospheric ducting system. The work will establish that ducts populated by prolific wave sources in the lower atmosphere are of considerable geophysical importance far from the source regions. The results will lead to the development of modeling capabilities for investigating ducting as a means of wave growth and the redistribution of wave energy between regions of the atmosphere, both vertically and horizontally. It will support coordinated multi-instrument investigations at existing sites, and provide a continuing research opportunity for a female scientist and a graduate student.
