Understanding and predicting the inner-core structure and intensity change of tropical cyclones (TCs) remains one of the
biggest challenges in tropical meteorology. This study addresses this challenge by investigating the formation, structure, and intensity
changes resulting from localized strong updrafts in TCs known as convective bursts (CBs). The evolution of CBs are analyzed in
high-resolution simulations of two hurricanes (Dean 2007 and Bill 2009) using the Weather Research and Forecasting (WRF) model. The
simulations are able to capture the observed track and peak intensity of the TCs. With Dean, there is a slight lag between the simulated
intensification and actual intensification, and the extreme rate of RI is not fully captured. However, the cycle of intensification,
weakening, and re-intensification observed in both TCs is captured in the simulations, and appears to be due to a combination of internal
dynamics and the surrounding environmental conditions. CBs are identified based on the 99th percentile of eyewall vertical velocity (over
the layer from z = 6-12 km) in each simulation (8.4 m s-1 for Dean, 5.4 m s-1 for Bill). The highest density of CBs is found in the
downshear-left quadrant, consistent with prior studies. The structure of the CBs is analyzed by comparing r-z composites of azimuths with
CBs and azimuths without CBs, using composite figures and statistical comparisons. The CB composites show stronger radial inflow in the
lowest 0-2 km, and stronger radial outflow from the eye to the eyewall in the 2-4 km layer. The CB composites also have stronger low-level
vorticity than the non-CBs, potentially due to eyewall mesovortices. The analysis of individual CBs also confirms the importance of the
eye-eyewall exchange in CB development, potentially by providing buoyancy, as parcel trajectories show that many parcels are flung outward
from the eye and rapidly ascend in the CBs, with as much as 500 J/kg of CAPE along the parcel path. In addition, the location of radial
convergence seems to play a key role in governing the radial location of CBs. Inner-core CBs seem to be associated with local convergence
maxima in the eyewall, while CBs outside the radius of maximum winds (RMW) are associated with convergence maxima due to bands and/or
secondary eyewalls. Analysis of intensity change in the simulations shows that there are more inner-core CBs during times when the TCs are
intensifying, while weakening/steady times appear to be associated with more CBs outside the radius of maximum wind (RMW), consistent with
observational studies and theoretical work. However, times when the TC has already been intensifying and continues to do so have more CBs
than times when the TC has been weakening but then intensifies. This suggests that CB development may not always be predictive, but rather
may sometimes occur as a result of ongoing intensification. On the other hand, rapid intensification (RI) in the simulations is found to
be associated with an even higher density of CBs inside the RMW than slower intensification. Lag correlations between CBs and intensity
are calculated to investigate the time of the intensity response to CB development. These calculations reveal a broad peak in correlation,
with the CBs tending to lead pressure falls by 0-3 hours. These results confirm the notion that convective heating inside the RMW is
favorable for intensification. The findings from this analysis show that eyewall CBs are driven by asymmetric dynamical processes in the
inner-core region of TCs, both in and above the TC boundary layer. In addition, the relationship between CB development and intensity
change is indeed positive, sometimes in a predictive sense, and at other times while intensity change is ongoing. / A Dissertation submitted to the Department of Earth, Ocean, and Atmospheric Science in partial
fulfillment of the Doctor of Philosophy. / Spring Semester 2016. / March 24, 2016. / Convection, Eye, Eyewall, Hurricane, Updraft, WRF / Includes bibliographical references. / Robert E. Hart, Professor Directing Dissertation; Irinel Chiorescu, University Representative;
Mark Bourassa, Committee Member; Henry Fuelberg, Committee Member; Guosheng Liu, Committee Member; Robert Rogers, Committee
Member.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_360367 |
| Contributors | Hazelton, Andrew Todd (authoraut), Hart, Robert E. (Robert Edward) (professor directing dissertation), Chiorescu, Irinel (university representative), Bourassa, Mark Allan (committee member), Fuelberg, Henry E. (committee member), Liu, Guosheng (committee member), Rogers, Robert Fulton (committee member), Florida State University (degree granting institution), College of Arts and Sciences (degree granting college), Department of Earth, Ocean, and Atmospheric Science (degree granting department) |
| Publisher | Florida State University, Florida State University |
| Source Sets | Florida State University |
| Language | English, English |
| Detected Language | English |
| Type | Text, text |
| Format | 1 online resource (263 pages), computer, application/pdf |
| Rights | This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s). The copyright in theses and dissertations completed at Florida State University is held by the students who author them. |
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