The investigators will generate a global climatology of mesosphere inversion layers (MILs) using satellite data. The climatology will be used to explore the source mechanisms for the layers and to establish their contributions to the dynamics of the middle atmosphere. MILs are fairly common occurrences in the mesosphere and lower thermosphere. Their signature is an increase in temperature with respect to altitude between 65 and 75 km or between 85 and 95 km. Satellite observations suggest that MILs can be long-lived and extend over tens of thousands of kilometers. Both ground-based and space-based datasets indicate that MILs are more common at low and middle latitudes than at high latitudes. The interest in MILs is sparked by their important implications for the energetics and composition of the middle atmosphere: they can significantly alter the propagation environment and the characteristics of gravity waves which in turn affects the mean flow and tidal structures. Since MILs appear to be fairly ubiquitous, their effects on gravity wave propagation may have to be considered in the formulation of gravity wave parameterization schemes for general circulation models. The climatology to be assembled will accomplish several goals: it will help establish the source mechanism for MILs which are not well understood; it will enable delineating the contributions of tides and planetary waves to the MILs as well as changes to the mean state caused by the fluxes of dissipating waves; and it will provide information on the MILs in a region where they have been rarely seen, the high northern latitudes. To produce the climatology, the project will utilize temperatures from satellites (the TIMED, NASA Aura, and the NIMBUS 7 missions) and from lidars at Fort Collins, Maui, and Arecibo. Airglow images from Bear Lake, Utah, will also be examined to infer information on gravity waves. The research activities address core CEDAR themes of dynamical coupling between the lower atmosphere and the upper atmosphere as well as coupling between different latitudes. The project is being led by a female scientist and will support the education and training of a science and engineering student. It will also promote collaborative activities between airglow, lidar, and satellite observing teams. The results of this investigation are expected to: (1) clarify the roles of tides and transient waves in MIL theory; (2) augment the knowledge of MIL occurrences in sparsely observed areas such as the high northern latitudes; (3) guide the interpretation of MILs and ducted gravity waves viewed from ground-based platforms; and (4) inform the middle atmosphere modeling community on potential impacts on gravity-wave breaking parameterizations.
