Eigenvector Analysis of Seasonal Temperature, Precipitation and Synoptic-Scale System Frequency over the Contiguous United States. Part II: Spring, Summer, Fall and Annual

Abstract

Eigenvector analysis was performed on spring, summer, fall and annual temperature and precipitation over the contiguous United States and on the frequency of occurrence of cyclonic and anticyclonic conditions over an area extending roughly from 60–130°W and 20–50°N. The first eigenvector in all cases represents anomalies of one sign over nearly all the contiguous United States. Correspondence of the other eigenvector forms across seasons was also good. These patterns appear to be associated with latitudinal shifts in the westerlies and to the amplitude and position of the long waves. An opposition in precipitation anomaly was found between the northwestern and southwestern United States which was mirrored in a similar pattern in variations of cyclone frequency over these two areas. Significant changes occurred in the frequency of occurrence of individual eigenvector forms, suggesting that particular circulation regimes may become established, persist and disappear in time. The length of time that a particular regime lasts is thus connected with regional changes in climate.