Date of Award

Spring 1-1-2019

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Aerospace Engineering Sciences

First Advisor

Lakshmi Kantha

Second Advisor

David Fritts

Third Advisor

Dale Lawrence

Fourth Advisor

Jeffrey Thayer

Fifth Advisor

Cora Randall

Abstract

Gravity waves are a dominant source of energy transport and coupling throughout the atmosphere. Transient gravity wave propagation effects and locally induced dissipation make significant contributions to the variability of temperature and wind evolutions over a broad range of spatial and temporal scales. Gravity wave impacts are particularly important to the mesosphere and lower thermosphere, where high wave amplitudes promote a range of complex, nonlinear interactions with the background environment at scales that are difficult to model and observe. An improved understanding of small-scale, temporally and spatially intermittent gravity wave interactions with variable local and large-scale environments is essential to improving how gravity wave dynamics are parameterized in mesoscale and global scale models.

This dissertation presents a comprehensive overview and analysis of the complex dynamics of high frequency atmospheric gravity wave and fine structure interactions in the mesosphere and lower thermosphere. Simulation studies are carried out to identify the fundamental dynamics of gravity wave-fine structure interactions in an idealized environment, evaluate the behavior of transient gravity wave propagation in an evolving background where linear assumptions break down, and determine the limitations of modeling gravity wave-fine structure interactions with the constraints of current mesoscale models. These studies utilize high resolution numerical simulations and improve the current understanding of gravity wave dynamics and their impact on the atmosphere.

Findings in these studies indicate that gravity wave-fine structure interactions have predictable dynamics that can be traced to the underlying vorticity characteristics set by the background environment. Gravity wave interactions with fine-structure background variations below gravity wave scales determine the formation of instability and induced wind characteristics, while gravity wave interactions with time evolving fine-structure variations larger than gravity wave scales account for intermittent forcing characteristics observed in the mesosphere and lower thermosphere. The dominant gradient characteristics of these interactions break down with insufficient spatial resolution, and the time dependent characteristics break down when under-resolved models apply viscous damping to constrain small scale motions. With proper consideration of the expected dynamics in a given environment, one can estimate the extent to which gravity wave-fine structure interactions contribute to the variability in under-resolved model simulations, identifying environments for which improved characterization would be beneficial.

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