A Comparison of 500 hPa Height Patterns Associated With Anticyclones of Pacific and Continental Origin Impacting The Central Gulf Coast, United States

Abstract

This research examines the 500 hPa circulation patterns that lead to the occurrence of days dominated by anticyclones of Pacific origin ("Pacific Highs") over the central Gulf Coast. Although the geographically preferred zones of greatest height variability are similar to those leading up to days dominated by anticyclones of continental origin ("Continental Highs"), variability centers on the northern fringes of the extratropics seem to support Pacific High activity to a greater extent than was found for Continental High events. The implication is that the presence of strong meridional flow is not necessary to advect a Pacific anticyclone to the Gulf Coast. However, composite flow pattern analysis reveals that slight upstream meridional flow has become more closely associated with Pacific High activity over the Gulf Coast from the 1961-1989 time period. Variability in 500 hPa flow leading up to Pacific High events is tied less directly to variability in surface weather variables than for Continental High events. These results are important because changes in surface atmospheric conditions predicted by GCMs are the result of circulation shifts, and the relationship between upper-level circulation shifts and the surface atmospheric response must be clearly understood.