[Eoas-seminar] M.S. Defense: Connor Stoll (Oct 16, 3 PM, Rm 1044)

[eoas-seminar at lists.fsu.edu]

Hi all,

It has been a relatively calm hurricane season so far, but if you are up for learning some hurricane dynamics this week...
Please join us for Connor's M.S. Defense this Thursday (October 16th) at 3 PM in Room 1044.
If you would like a Zoom link, just let me know.

Best,
Chelsea

M.S. defense presentation by Connor Stoll

Where: EOAS RM 1044
When: Thursday, October 16, 2025, at 3 PM

Advisor: Chelsea Nam
Committee: Allison Wing, Vasu Misra

Title: TROPICAL CYCLONE GENESIS PROCESSES IN MODERATE VERTICAL WIND SHEAR DEPENDING ON VERTICAL VORTEX PROFILES

Abstract:
Moderate vertical wind shear (VWS) presents significant challenges in forecasting tropical cyclone (TC) behavior due to its highly variable outcomes. This variability is particularly evident in TC genesis (TCG), an area with limited understanding due to sparse observations and uncertain model simulations. A primary issue associated with moderate VWS is the vortex tilt, displacement of low-level and mid-level vortex centers, leading to asymmetric TC structures. This study investigates the impact of vertical vortex structure on TC genesis under moderate VWS using numerical simulations with the Weather Research and Forecasting Model (WRF). There is variability in vertical profiles of pre-genesis vortices that serve as seeds for TCG. African Easterly Waves (AEWs) typically exhibit maximum vorticity near the mid-levels ($\sim$600 hPa), whereas Western Pacific Easterly Waves are characterized by low-level ($\sim$850 hPa) vortices. Our experimental design compares these two structures by centering the pre-genesis vortex at 600 hPa and 850 hPa, called Mid-Initiated and low-Initiated simulations respectively. We analyze variations in the timing of the genesis under moderate VWS and reduced moisture content. Mid-Initiated vortices tend to experience delayed genesis, often undergoing vortex reformation beforehand. In contrast, the timing of genesis in Low-Initiated vortices depends on the number of repeated, aligned precursor events; multiple failed attempts typically slow the onset of genesis. Key differences between Low-Initiated and Mid-Initiated ensembles include: (1) the Mid-Initiated members shows greater downshear left convection prior to genesis; (2) the Mid-Initiated members exhibits more evident vortex size expansion prior to genesis; (3) Mid-Initiated members display greater tilt at genesis, often necessitating a larger circulation and vortex reformation for successful development; (4) in Mid-Initiated runs, surface latent heat fluxes are more strongly aligned with the reformed vortex; and (5) they maintain higher stratiform coverage and deep-layer saturation fraction prior to genesis. These results together elucidate that Mid-Initiated vortices go through a different pathway with a greater role of mid-level vortex and low-level vortex reformation that was not apparent in Low-Initiated vortices in marginally favorable environments. The distinctive TCG pathways depending on initial vertical vortex profiles identified in this study will help enhance our TCG forecast accuracy in the low predictability regimes of moderate VWS.

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Chaehyeon Chelsea Nam, Ph.D.
Assistant Professor
Department of Earth, Ocean, and Atmospheric Science (EOAS)
Florida State University
RM 5011, ccnam at fsu.edu
https://chelsea-nam.github.io/<https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fchelsea-nam.github.io%2F&data=05%7C02%7Ceoas-seminar%40lists.fsu.edu%7C1ff1976f550a4ef3df3108de0a8983e3%7Ca36450ebdb0642a78d1b026719f701e3%7C0%7C0%7C638959782886399219%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=RHQPyPaHP%2FJSs%2FIKq%2B%2BAWYCsUTm60x9nNWBif%2BYoF5o%3D&reserved=0>



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