Type of Document Dissertation Author Ryglicki, David Ross Author's Email Address firstname.lastname@example.org URN etd-04152011-140027 Title The Evolution of Barotropically Unstable, High-Rossby Number Vortices in Shear Degree Doctor of Philosophy Department Earth, Ocean & Atmospheric Science, Department of Advisory Committee
Advisor Name Title Robert Hart Committee Chair T. N. Krishnamurti Committee Co-Chair Robert Ellingson Committee Member Vasu Misra Committee Member William Dewar University Representative Keywords
- vortex in shear
Date of Defense 2011-03-22 Availability unrestricted AbstractThe role of mesovortices in the eyewalls of sheared unstable, high-Rossby number vortices is investigated. A high-resolution numerical model is used to simulate dry vortices in an attempt to unite ideas from previous works. The simulations are used to investigate the dynamical, adiabatic interactions between potential vorticity (PV) mixing dynamics and shear forcings of barotropically unstable, high-Rossby number barotropic vortices. Previous work has investigated barotropic vortices in shear, while other previous work has studied barotropically unstable ring vortices. This work will combine those two avenues of research by shearing barotropically unstable barotropic ring vortices because ring vortices are more representative of tropical cyclones.
Quantitative and qualitative analysis of the tilt and of the internal dynamics are presented. Using such as metrics as PV power spectra, PV palinstrophy, and a linear energy equation that incorporates the effects of the shear forcing, it is found that impact of the shear forcing on the initial breakdown of the ring is merely slight; however, the breakdown of the ring of high PV into smaller mesovortices – and the subsequent rearrangement of PV into a monopolar structure – is quite significant when considering the tilt evolution. As the vortex mixes, the storm weakens. This acts as a detriment to the ability of the vortex to keep itself upright and resistant to the shear forcing, as the penetration depth of each layer of the vortex decreases to below the scale height after mixing. In terms of the energetics, it is found that the barotropic energy conversion term is consistently the largest, which is expected. When sheared, the shear forcing acts to generally counteract the effects of mixing and reduce eddy kinetic energy. Additionally, it is found that the shear forcing induces a trochoidal oscillation at levels of highest background flow.
The sensitivity of the results is investigated by comparing and contrasting two different centroid metrics - a pressure-ring centroid and a PV-cubed centroid. PV centroid metrics historically have been used to investigate inner-core tilt while geopotential centroid metrics have been to used to investigate larger-scale tilt. For the first time, these two approaches are being compared and contrasted. It is found that during a dynamical mixing event, the PV centroid is not very resistant to the rapidly changing inner-core PV field, and that this has nontrivial effects on the calculations of center-sensitive fields such as Fourier decompositions in the azimuth and determining radial and tangential wind structures. When using a pressure-ring centroid centeredon a pressure contour that resides far enough outside the core yet radially inward enough not to be impacted by the environment, it is found that this method is much more resistant to inner core processes.
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