Linear Relation of Central and Eastern North American Precipitation to Tropical Pacific Sea Surface Temperature Anomalies

In past research the Southern Oscillation index has often been used as an indicator of the tropical Pacific climate, notably for El Niño and La Niña event occurrences. This study identifies calendar monthly teleconnection signals in central and eastern North American precipitation associated with an alternative tropical Pacific indicator, sea surface temperature anomaly (SSTA) patterns. Using an approximate 1° resolution set of monthly precipitation totals for 1950–92, the work identifies monthly teleconnection relationships and their intraseasonal evolution. This builds upon previous studies that were limited to seasonal timescales. Here, a unique two-way statistical analysis is used to delineate linear SSTA–precipitation teleconnection patterns. First, a principal component analysis (PCA) is performed on a monthly tropical Pacific SSTA dataset for 1950–92 to identify the coherent modes of variability. The principal component (PC) score time series representing the most significant modes of SSTA variability (see below) are then correlated on a calendar-monthly basis with station precipitation anomalies, yielding associated “correlation-based” precipitation coherencies. In the second approach, PCA is applied to the precipitation anomaly data for each calendar month. Then, the resulting “PC-based” precipitation coherencies most central to each of the major correlation-based precipitation regions are identified, and their associated PC score time series are subsequently correlated with the tropical Pacific SSTA grid-cell data, yielding correlation-based SSTA coherencies that are then compared (generally favorably) with their PC-based forerunners. The three SSTA PC patterns used to seek teleconnection signals in central and eastern North American precipitation are the first unrotated PC (UPC1, emphasizing central tropical Pacific variability), and the first (VPC1, eastern tropical Pacific) and second (VPC2, western to north central tropical Pacific) Varimax-rotated PCs. The strongest such signals to emerge were for precipitation in the southeastern United States (positive association with UPC1 and VPC1 in November–March), Texas (positive association with UPC1 and VPC1 in November–March), the Great Lakes/Ohio River region (negative association with UPC1 and VPC1 in January–March), the southeastern United States (negative association with UPC1 and VPC1 in July–August), the southern Canadian prairie (negative association with UPC1 and VPC1 in November–January), and along a northern storm track (positive association with VPC2 in September–October). These results, derived from new datasets using a unique statistical approach, both broadly confirm and significantly clarify previous findings and present striking new associations.