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The Influence of Regional-Scale Circulation on Precipitation Variability in the Southern United States

Vega, Anthony Jude

Titre : The Influence of Regional-Scale Circulation on Precipitation Variability in the Southern United States

Auteur : Vega, Anthony Jude

Université de soutenance : LOUISIANA STATE UNIVERSITY

Grade : Doctor of Philosophy (PhD) 1994

The proximity of the southern United States to large water bodies, mountain systems, and the arid climate of the desert southwest makes extended precipitation forecasts exceedingly difficult. In order to better understand the complex precipitation mechanisms, this analysis addresses the relationships between the regional-scale circulation and long-term precipitation variability and change in the southern US for each season through a 42 year study period. Five unique precipitation regions were created for each season, and seasonal anomalies were calculated and examined by region for changes in variability and slope through time. Long -term climate change was detected in the precipitation regions only during the autumn season. During autumn, the western regions showed a significant increase in precipitation through the study period while the eastern region recorded a significant decrease. To explain the significant variations and trends, relationships with the mean hemispheric flow regimes were analyzed. Atmospheric teleconnection indices and a formulated regional-scale flow index were correlated to the regional precipitation anomalies. Results indicated that the regional -scale flow index was the best estimator of regional precipitation variability during every season. To investigate the influence of the regional-scale circulation further, isolation of the primary circulation anomalies associated with the Atlantic Subtropical High (STH) was necessary. Results indicated the importance of five dominant circulation regimes which transcend the seasonal analysis. Three of the patterns related to variations in the STH while two related to variations in the generalized hemispheric longwave flow. Of these, the most important patterns with respect to changes in precipitation related to variations in the STH, especially during the autumn season. It was found that strengthening of the STH over the eastern US causes persistent drought while advecting moisture into the continental interior. Position of the STH anomaly is critical to the corresponding precipitation regime as an eastward displaced STH causes negative precipitation anomalies in the western regions and positive precipitation anomalies in the east. This analysis proves the importance of regional-scale circulation variation on the precipitation variability of the US south. Given current global warming predictions, studies which fully integrate regional-scale atmospheric circulation variability are crucial to future impact scenarios.


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