Surface and 700 hPa Atmospheric Circulation Patterns for the Great Lakes Basin and Eastern North America and Relationship to Atmospheric Teleconnections

Abstract

Many studies have identified continental-scale atmospheric circulation regimes, and some have been employed for various regions, but none have involved a regional categorization of circulation around the Great Lakes basin. Such an analysis is important not only because of the economic and recreational importance of the lakes, but in an effort to relate the regional circulation types to the broaderscale modes of atmospheric circulation, such as that forced by El Niño (ENSO). In this study, rotated principal components analysis (RPCA) is performed on the monthly mean sea-level pressure field around the Great Lakes basin, and in a separate analysis, on the mean 700 hPa field in eastern North America. An average-linkage clustering algorithm is applied to the RPCA scores to classify the monthly surface circulation in the Great Lakes region and the 700 hPa circulation over eastern North America. The classification is used to determine whether the various categories of regional circulation patterns are coincident with distinct hemispheric-scale flow regimes. To do this, indices of the modes of variability in some of the most well-known atmospheric teleconnections during months that fall within each circulation mode are subjected to ANOVA tests by cluster. Results suggest that the regional atmosphere over the Great Lakes basin undergoes long-term shifts in preferred modes of circulation. Furthermore, flow variability associated with the 700 hPa North Atlantic Oscillation (NAO) and Pacific/North American (PNA) teleconnections are more strongly tied to variability in both the Great Lakes regional surface circulation and the 700 mb eastern North American flow regimes than is the ENSO-forced Southern Oscillation.