Equatorial waves have been studied extensively due to their importance to the tropical climate and weather systems.
Historically, their activity is diagnosed mainly in the wavenumber-frequency domain. Recently, many studies have projected observational
data onto parabolic cylinder functions (PCFs), which represent the meridional structure of individual wave modes, to attain time-dependent
spatial wave structures. The non-orthogonality of wave modes has yet posed a problem when attempting to separate data into wave fields
where the waves project onto the same structure functions. We propose the development and application of a new methodology for equatorial
wave expansion of instantaneous flows using the full equatorial wave spectrum. By creating a mapping from the meridional structure
function amplitudes to the equatorial wave class amplitudes, we are able to diagnose instantaneous wave fields and determine their
evolution. Because all meridional modes are shared by some subset of the wave classes, we require constraints on the wave class amplitudes
to yield a closed system with a unique solution for all waves' spatial structures, including IG waves. A synthetic field is analyzed using
this method to determine its accuracy for data of a single vertical mode. The wave class spectra diagnosed using this method successfully
match the correct dispersion curves even if the incorrect depth is chosen for the spatial decomposition. In the case of more than one
depth scale, waves with varying equivalent depth may be similarly identified using the dispersion curves. The primary vertical mode is the
200 m equivalent depth mode, which is that of the peak projection response. A distinct spectral power peak along the Kelvin wave
dispersion curve for this value validates our choice of equivalent depth, although the possibility of depth varying with time and height
is explored. The wave class spectra diagnosed assuming this depth scale mostly match their expected dispersion curves, showing that this
method successfully partitions the wave spectra by calculating wave amplitudes in physical space. This is particularly striking because
the time evolution, and therefore the frequency characteristics, is determined simply by a timeseries of independently-diagnosed
instantaneous horizontal fields. We use the wave fields diagnosed by this method to study wave evolution in the context of the
stratospheric QBO of zonal wind, confirming the continuous evolution of the selection mechanism for equatorial waves in the middle
atmosphere. The amplitude cycle synchronized with the background zonal wind as predicted by QBO theory is present in the wave class fields
even though the dynamics are not forced by the method itself. We have additionally identified a time-evolution of the zonal wavenumber
spectrum responsible for the amplitude variability in physical space. Similar to the temporal characteristics, the vertical structures are
also the result of a simple height cross-section through multiple independently-diagnosed levels. / A Dissertation submitted to the Geophysical Fluid Dynamics Institute in partial fulfillment of the
requirements for the degree of Doctor of Philosophy. / Spring Semester 2016. / March 23, 2016. / QBO, Tropics, Waves / Includes bibliographical references. / Ming Cai, Professor Directing Dissertation; Xufeng Niu, University Representative; Allan Clarke,
Committee Member; Kevin Speer, Committee Member; Philip Sura, Committee Member.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_360319 |
| Contributors | Barton, Cory (authoraut), Cai, Ming (professor directing dissertation), Niu, Xufeng (university representative), Clarke, Allan J. (committee member), Speer, Kevin G. (Kevin George) (committee member), Sura, Philip (committee member), Florida State University (degree granting institution), College of Arts and Sciences (degree granting college), Program in Geophysical Fluid Dynamics (degree granting department) |
| Publisher | Florida State University |
| Source Sets | Florida State University |
| Language | English, English |
| Detected Language | English |
| Type | Text, text |
| Format | 1 online resource (98 pages), computer, application/pdf |
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