[Eoas-seminar] Meteorology PhD Defense for Sweta Das, December 5, 2019, 3:30 PM, Love 353

[eoas-seminar at lists.fsu.edu]

Meteorology Seminar

Sweta Das

PhD Meteorology Candidate



Title:  Understanding the evolution of Tropical Cyclones through the streamfunction-velocity potential framework


Major Professor:  Dr. Vasu Misra
Co-Advisor: Dr. Guosheng Liu

Date: December 5th, 2019                                 Time: 3.30 PM



Location: Werner A. Baum Seminar Room (353 Love Building)
(Please join us for refreshments served outside room 353 Love @ 3:00 PM)

ABSTRACT
The understanding of the evolution of a Tropical Cyclone (TC) has been a topic of research for several years. During the hurricane season not all thunderstorm events embedded in the African easterly waves or otherwise evolve into organized convection with a closed low pressure system, manifesting into TCs. In this work we suggest that one of the ways to objectively analyze the evolution of the TC is to understand the evolution of the conversion of the available potential energy into kinetic energy on the scale of the disturbance. This study explores the energetics of the interaction between Streamfunction (Psi[cid:image001.png at 01D5A9C0.99D202F0])- Velocity Potential (Chi: [cid:image002.png at 01D5A9C0.99D202F0] ) in the numerical simulations of the TCs.
Using the output of separate 48-hour WRF simulations of three Atlantic TCs: Cindy and Irma of 2017, and Michael 2018, we analyze the time history of the conversion of their kinetic energy from the irrotational to the non-divergent components of the winds. All of these TCs had varied intensities with Cindy being the weakest and Irma being the strongest over the simulation period, which WRF simulated with reasonable fidelity in the evolution of their peak intensities. We show that at 850hPa, the fractional conversion of the kinetic energy from the irrotational to the non-divergent component of the wind increases as the TC intensifies and is higher for the stronger TCs than weaker TCs. Contrastingly, in the outflow level of the TC this transfer of kinetic energy is weaker for stronger TCs than the weaker TCs. Our analysis reveals that when the gradients of the streamfunction and velocity potential are large and oriented parallel to each other both in the large-scale TC environment and in the region of the primary circulation of the TC, then the TC is favored to intensify with robust conversion of the kinetic energy of the irrotational flow[cid:image003.png at 01D5A9C0.99D202F0] to kinetic energy of non-divergent flow ([cid:image004.png at 01D5A9C0.99D202F0] ) at 850hPa. In contrast, however in the outflow layer, we require a slower conversion of [cid:image005.png at 01D5A9C0.99D202F0]  to [cid:image004.png at 01D5A9C0.99D202F0]  for a TC to intensify otherwise it leads to increased inertial instability and weakening of the TC. We arrive at similar conclusions when we contrast the evolution of the tropical cyclones from its genesis to intensifying stages. Likewise, when we examine the sensitivity of the simulations of the tropical cyclones to the choice of microphysics, we find that parameterizations that engenders strong conversion of  [cid:image005.png at 01D5A9C0.99D202F0]  to [cid:image004.png at 01D5A9C0.99D202F0]  at 850 hPa and weak conversion of [cid:image005.png at 01D5A9C0.99D202F0]  to [cid:image004.png at 01D5A9C0.99D202F0] at the outflow level leads to the simulation of stronger TCs. Therefore, analyzing this conversion rate of kinetic energy of the flow field helps in understanding the evolution of the intensity of TCs.



Shel McGuire
Florida State University
Academic Program Specialist
Department of Earth, Ocean, & Atmospheric Science
1017 Academic Way, 410 Love Building (Meteorology)
Tallahassee, FL 32306
850-644-8582




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