Abstract:
The Southeastern United States is a region where increases in temperature have been largely muted when compared to other regions of the country, although extremes in both temperature and precipitation have become more common over time. In the first part of this research, the strength and recurrence of Southeastern United States intense precipitation events (IPEs) was analyzed annually, seasonally, and sub-regionally with an emphasis on identifying trends and causal mechanisms at each of these temporal and spatial scales. Causal mechanisms responsible for IPE were investigated by utilizing the Spatial Synoptic Classification (SSC) to determine which surface weather types are associated with these events. Furthermore, a case study analysis of the most intense IPE in each physiographic province was performed with archived daily surface maps to classify the type of surface forcing mechanism that was responsible for the most exceptional IPE in each physiographic province. Results showed a statistically significant and regionally variable increase in both the recurrence and strength of IPE. A statistically significant increase in the number of moist tropical (MT) weather type IPEs per year was identified, and attributed to more common northward and inland encroachment of these events. Case study reveals that coastal areas depend heavily on tropical events and stationary fronts, while forcings in inland areas are more evenly distributed. In addition to surface characteristics, the second part of this research explored synoptic patterns found with the most intense IPE across the entire study area. Principal Component Analysis, and Cluster Analysis were employed with 500 and 850 mb geopotential heights and a variety of seed variables in subsequent analyses to discover distinct types of IPE. A manual classification based on IPE origin as either a warm or cold core system, and formation location of the IPE provided the best representation of the synoptic patterns responsible for types of IPE. These IPE types were portrayed via a series of mean flow maps of 500 and 850 mb geopotential height, sea level pressure, and 72 hour mean precipitation. The precipitation amounts of the 72 hour means for the five IPE types were statistically significantly different from each other.
