[Eoas-seminar] MS Defense - Geiger

[eoas-seminar at lists.fsu.edu]

Good afternoon,

Please join us for Melody Geiger's MS Defense on Thursday, March 12th from 11:00 AM - 12:30 PM (EST).

Title: Evaluating GLM-Derived Lightning Activity in Hurricane Milton (2024) as a Tool for Forecasting Rapid Intensification

Name: Melody Geiger
Date: March 12th, 11:00 am - 12:30 pm
Location: EOAS 3067
Major Professor: Dr. Henry Fuelberg

Abstract: Rapid intensification (RI) of tropical cyclones is a difficult process to forecast, due to the complex physical processes involved. Several theories exist in the current literature about predicting RI before it occurs, including the role of lightning activity in a tropical cyclone. It is theorized that an increase in lightning in the inner core of a tropical cyclone can be an indicator of RI. However, there is debate among researchers about whether lightning may serve as a useful predictor of RI onset, an indicator that RI is already underway, or a signal that RI is ending. This research presents a case study on Hurricane Milton, which underwent RI in October 2024. Hurricane Milton intensified from a tropical depression to a category 5 hurricane in only 48 h and 55 min. GOES Lightning Mapper (GLM) products are used to examine the lightning activity of Hurricane Milton. Three GLM products are utilized concurrently; flash extent density, total optical energy, and minimum flash area. A significant advantage of using GLM data is that this satellite-based instrument provides high resolution data over the open ocean, which is a shortcoming of traditional ground-based lightning detection networks. Three 12 h intensification periods and one 12 h weakening period are defined and analyzed: two periods of moderate intensification, one period of rapid intensification, and one weakening period. This thesis focuses on these intensification and weakening periods to establish whether lightning observations may be used as a tool for improving tropical cyclone intensity forecasts. Results are compared to other case studies in the current literature that utilize GLM data in regard to tropical cyclone intensity.

Results show that for Hurricane Milton, inner-core lightning can be used as a predictor of RI within approximately 6 h prior to maximum intensity. Lighting in the rainbands can be used as a predictor of RI within approximately 6-12 h prior to maximum intensity. These findings are supported by correlation analyses, which show that peaks in lightning activity are significantly correlated with peak wind speed at varying lead times. At the start of the RI period, lightning activity increases significantly and becomes concentrated on the inside of the radius of maximum winds (RMW). During this period, flash extent density and total optical energy increase while minimum flash area decreases. When examining the lightning activity in a shear-relative framework, the RI period is characterized by a shift in lightning activity to the right side of the shear vector. As Milton begins to weaken, the minimum flash area increases while the flash extent density and total optical energy decrease.  In addition, the lightning noticeably shifts to the down-shear left quadrant, regarding a shear-relative framework. Relative to the RMW, the lightning becomes more dispersed and transitions outside the RMW.  Many of these results are comparable with prior GLM-based case studies, while any notable differences are also discussed in this thesis. Although this thesis examines a single tropical cyclone, the results provide additional evidence that lightning- particularly the spatial distribution, density, energetics, and size of the flashes- contains useful information about the timing of rapid intensification. This work contributes to the ongoing debate regarding whether or not lightning observations can be used as a predictive tool in tropical cyclone intensity forecasting.

Best,
Adea

Adea Arrison
Sr. Academic Program Specialist
Department of Earth, Ocean & Atmospheric Science
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