Ashley, Walker S.
M.S. (Master of Science)
Department of Earth, Atmosphere and Environment
The effects of climate change may influence the prevalence of regional atmospheric conditions supportive of hazardous convective weather (HCW). As a result, the possibility of an increase in the frequency, strength, and/or variability of thunderstorms and their high-impact hazards—including tornadoes, damaging winds, hail, and flash flood-producing downpours—has garnered much scientific and public interest. Radar reflectivity, which remotely assesses precipitation intensity, may be used to detect, track, catalog, and appraise HCW and their parent storms over broad spatiotemporal scales. Reflectivity may also be simulated with regional climate models, and recent, but limited, efforts using these simulation output have identified the potential for increases in the intensity, occurrence, and variability of storms such as mesoscale convective systems.
This study sought to investigate characteristics and trends in reflectivity thresholds from regional climate simulation output generated for an early 21st century period and a late-century period under a high anthropogenic emissions pathway for the conterminous U.S. Meteorologically significant thresholds served as proxies for storm intensity, and, when assessed in aggregate, provided unique perspectives how intense precipitation events, such as severe thunderstorms, may change in occurrence, character, and variability in the 21st century. Initially, an observed radar dataset was used to create a 15-year climatology of reflectivity threshold exceedance frequencies. Then, 15-year reflectivity climatologies were assessed for two climate simulation periods—1990 – 2005 (HIST) and 2085 – 2100 (FUTR)— followed by comparisons of reflectivity distributions between the two 15-year simulation epochs. Results showed that in an elevated greenhouse gas concentration scenario, convection may become more intense and frequent in the spring and late summer months, compounded by increased monthly variability of their occurrences throughout all reflectivity thresholds. Increases in daily reflectivity exceedance values from early to late century epochs were particularly large for high reflectivity thresholds, suggesting that potentially impactful storms may become more numerous during the 21st century under an enhanced greenhouse gas emission scenario. Additionally, throughout all months, a greater degree of variability in sub-convective and convective reflectivity exceedances was found in the future epoch. The reflectivity climatologies in this study provide a perspective on possible 21st century trends of precipitation intensity, while also offering a point of comparison for future simulation research examining potential changes in climatology of precipitation intensity in the U.S.
Battisto, Christopher Michael, "Trends in Observed and Simulated Radar Reflectivity for the 21st Century" (2021). Graduate Research Theses & Dissertations. 6847.
Northern Illinois University
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