Doctor of Philosophy (PhD)


Geography and Anthropology

Document Type



Terrestrial Gamma-ray Flashes (TGFs) are sub-millisecond bursts of the highest naturally occurring light-energy found within Earth’s atmosphere. TGFs are associated with the electric fields produced in thunderstorms and are geolocated by coincident sferics from lightning strokes. Though billions of lightning strokes occur globally each year, fewer than 1,000 TGFs are detected via satellite and ground-based sensors and only a small fraction are geolocated via sferics.

To date, few studies have focused on individual thunderstorms and climates that produce TGFs. This dissertation examines TGFs from two differing data samples: 1) NASA's Fermi Gamma-Ray Burst Monitor (2013-2018) and 2) The TGF and Energetic Thunderstorm Rooftop Array (TETRA-II) (2016-2019) as a means to identify influences of climate, topography, and electric and atmospheric conditions that produce TGFs.

Getis Ord Gi* and Anselin Moran's I spatial cluster analyses reveal several statistically significant cluster patterns of the 1,341 sferic-associated TGFs detected in tropical latitudes by Fermi. Clusters tend to occur in coastal areas heavily influenced by land-sea interaction. A disproportionate number of Fermi TGFs (65\%) occur over ocean, where lightning is infrequent. Additionally, TGFs in this sample do not necessarily coincide with the highest lightning dense regions, suggesting the production of TGFs require a specific atmospheric conditions rather than occurring as a ratio function of lightning activity.

TETRA II detected 20 sferic-associated TGF events across three detector arrays in tropical and subtropical climates. An examination of lightning frequency within 10 km of TETRA II indicates that events occur within mature thunderstorm cells exhibiting both high and low frequency lightning flash rates (1-46 flashes/min) within(8km-15.5km). One low-altitude, cold-weather event confirms a probable satellite detection bias as proposed by Chronis et al. 2016. NEXRAD-monitored events occur withinproduction, a relationship to the development of the mixed-phase updraft region is present.



Committee Chair

Trepanier, Jill