| Summary: | 2017 Summer. Includes bibliographical references. Tornadoes that occur during the cold season, defined here as November–February (NDJF), pose many unique societal risks. For example, people can be caught off-guard because in general one does not expect severe weather and tornadoes during winter months. The public can also be unsuspecting of significant weather due to the bustle of major holidays like Thanksgiving, Christmas, and New Year's, when most people are concerned with family activities and not thinking about the weather. Cold-season tornadoes also have a propensity to be nocturnal and occur most frequently in the South and Southeastern U.S., where variable terrain, inadequate resources, and a relatively high mobile home density add additional social vulnerabilities. Over the period 1953–2015 within a study domain of (25-42.5°N, 75-100°W), some 937 people lost their lives as a result of NDJF tornadoes. Despite this enhanced societal risk of cold-season tornadoes in the South, very little attention has been given to their meteorological characteristics and climate patterns, and public awareness of their potential impacts is lacking. This thesis aims to greatly advance the current state of knowledge of NDJF tornadoes by providing an in-depth investigation from three different science perspectives. First, a climatology of all (E)F1-(E)F5 NDJF tornadoes is developed, spanning the period 1953–2015 within a domain of (25-42.5°N, 75-100°W), in order to assess frequency and spatial changes over time. A large increasing trend in cold-season tornado occurrence is found across much of the Southeastern U.S., with the greatest uptick in Tennessee, while a decreasing trend is found across eastern Oklahoma. Spectral analysis reveals a cyclic pattern of enhanced NDJF counts every 3-7 years, coincident with the known period for ENSO. Indeed, La Niña episodes are found to be correlated with NDJF tornado counts, although a stronger teleconnection correlation exists with the Arctic Oscillation (AO), which explains 25% of ...
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