CEDAR Postdoc: Analysis and Modeling of Breaking Short Period Gravity Waves and Their Effects on the Dynamic Mesosphere and Lower Thermosphere

Utah State University, Logan UT

Investigators

Abstract

This project will conduct a modeling and observational study to investigate the breaking of short-period gravity waves and the resulting energy and momentum deposition under realistic wind and thermal conditions in the mesosphere and lower thermosphere region. Short-period (> 5-30 min), small-scale (> 10-100 km) gravity waves provide a significant fraction of wave energy throughout the middle and upper atmosphere. These include waves which propagate horizontally and vertically and, at shorter periods, those which are ducted by large-scale thermal or wind structure to propagate horizontally. Such waves are generated by a broad range of processes, including tropospheric forcing often associated with convective weather systems and thunderstorms, and in situ forcing due primarily to localize convective and shear instabilities, or to nonlinear resonant interactions. Through extensive ground-based observations of mesopause airglow modulation by gravity waves, in conjunction with numerical and theoretical modeling studies, understanding of small-scale gravity wave generation, propagation, and directionality/seasonality has improved significantly over recent decades. However, very little is currently known about the final deposition of energy and momentum via breaking of short-period gravity wave packets, particularly those which are strongly controlled by background atmospheric structure. The project will focus on two particular questions to address this gap in understanding: (1) How does the large-scale dynamic structure of the mid-latitude mesosphere/lower thermosphere dictate the stability and breaking of short-period gravity waves? (2) How does breaking or dissipating short-period gravity waves modify the local mesosphere/lower thermosphere structure through momentum and energy deposition? To answer these questions, a combined numerical and observational study will be carried out. Utilizing recent, two-dimensional, fully-nonlinear models of gravity wave propagation and airglow modulation, the role and effects of atmospheric instability and wave breaking will be explored for short-period gravity waves under quasi-realistic conditions. This will be complemented by airglow image data-sets together with available radar and lidar wind data to determine the role of background dynamics on short-period wave breaking, and overall atmospheric dynamic stability. The broader impact of the project is that it supports the efforts of a new Ph.D. recipient who has developed one of the models to be used. The quantification of energy and momentum deposition by short period gravity waves resulting from this project will benefit mesosphere/lower thermosphere science.