Date of Award

Spring 1-1-2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Aerospace Engineering Sciences

First Advisor

David C. Fritts

Second Advisor

Jeffrey Thayer

Third Advisor

Jeffrey M. Forbes

Fourth Advisor

Scott E. Palo

Fifth Advisor

Al Gasiewski

Abstract

Gravity waves (GWs) play an important role in the dynamical processes of Earth’s atmosphere. Momentum transport and deposition accompanying GW propagation and dissipation cause body forces that alter large-scale winds, and induce residual circulations from the troposphere into the mesosphere and lower thermosphere (MLT) and above. While these influences on mean state climatology are understood qualitatively, there remains a need for a more complete understanding of GW dynamics and their effects throughout the atmosphere. Small horizontal-scale GWs, especially those with large vertical wavelengths, account for a significant fraction of the total momentum fluxes (MFs) and the forcing of larger-scale motions. Yet these small-scale GWs are largely unresolved in global models and poorly described by parameterizations at present. Thus, a better understanding of small-scale GW (horizontal wavelengths < 100 km) dynamics and their influences on the momentum budget of the MLT is a major need.

This dissertation addresses small-scale GW dynamics and MFs in the MLT in variable environments using new state-of-the-art instrumentation. Data were provided by sodium resonance lidars, Advanced Mesospheric Temperature Mappers (AMTMs), and correlative instruments at the ALOMAR ground-based observatory in northern Norway, and employed during the Deep Propagating Gravity Wave Experiment (DEEPWAVE) performed in New Zealand in 2014. These data enabled quantification of multi-scale GW environments in which larger-scale motions have strong influences on the propagation, evolution, MFs, and momentum deposition of smaller-scale GWs.

Results from ALOMAR revealed strong influences on small-scale GW propagation and MFs by variable large-scale wind and temperature fields, yielding variable propagation and ducting conditions, and occasional very large, local MFs. GW characterization and MF estimates using DEEPWAVE data likewise revealed a tendency for the largest MFs to be associated with smaller horizontal-scale GWs, often having magnitudes of many times larger than mean values in the MLT. DEEPWAVE measurements above regions of MW breaking also revealed apparent secondary GW generation, indicating more complex GW roles in momentum transport that must have significant, though unknown, implications at much higher altitudes.

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