Joshua Hostler Ph.D. defense
10 a.m. Wednesday, Oct. 14
401 Akasofu Building
Also available via Zoom
In partial completion of the Ph.D. in Atmospheric Sciences from the University of Alaska Fairbanks College of Natural Science and Mathematics, Department of Atmospheric Sciences
Dissertation title: Seasonal Prediction of Lightning for Alaska’s Wildland Fire Season
Abstract: While lightning-ignited fires account for 97.5% of the burned area in Alaska, seasonal forecasts critical for planning fire management resources do not include a lightning component. Long-range dynamical forecasts are not capable of resolving the physical processes that are commonly used to parameterize lightning and the observational lightning record is too short to support a statistical outlook. Large-scale weather patterns, identified with the self-organizing map (SOM), are associated with daily lightning intensities. March-initialized long-range dynamical forecasts of these weather patterns are then used to construct a forecast of June–July high-lightning days (HLDs) for the East and West Boreal regions. The regime-based forecasts are significantly correlated with observed HLD counts in the East Boreal (r=0.58, p<0.01) and positive (but not significant) for all configurations in the West Boreal. To support a statistical forecast, a histogram gradient-boosted tree is used to construct a proxy lightning record from 1959–2025 based on atmospheric reanalysis data. The proxy lightning record is significantly correlated (p<0.05) with observations in 80% of grid cells (field significant at p<0.01) and significantly correlated (r=0.38, p<0.01) with the March–April Pacific North American (PNA) pattern in East Boreal Alaska, an effect that was too small to detect with the 22-year observational record. Snowoff timing is consistent with partial mediation of the PNA–lightning relationship. Persistent Gulf of Alaska SSTs and June Beaufort sea-ice area are also plausible mechanisms but fall below significance at the p<0.05 level when controlling for the PNA. These results constitute the first skillful forecasts of lightning for Alaska's wildland fire season.
Major advisor: Uma Bhatt