Surface and 700 hPa atmospheric circulation patterns for the Great Lakes basin and eastern North America and relationship to atmospheric teleconnections

Many studies have identified continental-scale atmospheric circulation regi mes, and some have been employed for various regions, but none have involve d a regional categorization of circulation around the Great Lakes basin. Su ch an analysis is important not only because of the economic and recreation al importance of the lakes, but in an effort to relate the regional circula tion types to the broader-scale modes of atmospheric circulation, such as t hat forced by Fl Nino (ENSO). In this study, rotated principal components a nalysis (RPCA) is performed on the monthly mean sea-level pressure field ar ound 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 Ameri ca. The classification is used to determine whether the various categories of regional circulation patterns are coincident with distinct hemispheric-s cale 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. Resul ts suggest that the regional atmosphere over the Great Lakes basin undergoe s long-term shifts in preferred modes of circulation. Furthermore, flow var iability associated with the 700 hPa North Atlantic Oscillation (NAO) and P acific/North American (PNA) teleconnections are more strongly tied to varia bility in both the Great Lakes regional surface circulation and the 700 mb eastern North American flow regimes than is the ENSO-forced Southern Oscill ation.