AIR MASS FREQUENCY, TRENDS, AND STAGNATION IN THE SOUTHERN APPALACHIAN REGION OF THE U.S.A., 1965–2014

Recent research suggests that accelerated Arctic warming reduces the thermal gradient between polar and tropical regions and weakens the mid-latitudinal jet stream. A weakened jet produces deep troughs and synoptic-scale blocking, which results in the persistence of air masses in the high- to mid-latitudes of the northern hemisphere. Studies across the United States and Canada have documented a decline in the frequency of air mass transition (TR) days. This study analyzes air mass frequency, trends, and stagnation in the Southern Appalachian region of North America. This study places particular emphasis on the persistence of life-threatening air mass types, defined as those that contribute to extreme weather and poor air quality days. Analyses are conducted using 50 years of daily synoptic weather-type classifications (Spatial Synoptic Classification, SSC) from four study locations in Southern Appalachia. No such study has previously been conducted for the Southern Appalachian region. Results of this study show some significant frequency trends in air masses. Most notably, dry polar (DP) days are declining, and dry tropical (DT) days are increasing. Though expected to change significantly, the frequencies of moist tropical (MT) days and TR days show no distinct trend. Changes in the stagnation frequency of potentially oppressive types MT and DP vary by location, and stagnation duration has slightly increased at all stations for the two types. Overall, it seems as though the region is trending toward a warmer, drier climate with more frequent, longer stagnation events. This study serves as a foundation for future studies concerning the impact of climate change on the southeastern United States, Great Smoky Mountains National Park, and residents and visitors in the region.