Observed Nonlinearities of Monthly Teleconnections between Tropical Pacific Sea Surface Temperature Anomalies and Central and Eastern North American Precipitation

Abstract

Most investigations of relationships between tropical Pacific sea surface temperature anomaly (SSTA) events and regional climate patterns have assumed the teleconnections to be linear, whereby the climate patterns associated with cold SSTA events are considered to be similar in structure and morphology but opposite in sign to those linked to warm SSTA events. In contrast, and motivated by early evidence of nonlinearity in the above regard, this study identifies characteristic (i.e., composite) calendar monthly central and eastern North American precipitation patterns separately for warm and cold SSTA events in different regions of the tropical Pacific (central, eastern, west-central“horseshoe,” far western) identified through principal component analysis. The precipitation anomaly patterns are computed from an approximately 1° lat–long set of monthly station data for 1950–92. Their robustness and nonlinearity are established using local, regional, and field statistical significance tests and a variance analysis. This combination of unique SSTA analyses, resulting composite selection, and characteristic precipitation anomaly determination from a fine-resolution dataset increases our understanding of tropical Pacific–North American precipitation teleconnections in several respects. First, significant linkages to the two SSTA modes related to traditional warm and cold events (central and eastern tropical Pacific) are identified for all months except September and October, with all exhibiting some nonlinear characteristics. The most important of those nonlinearities involve associations with eastern tropical Pacific SSTAs, which affect precipitation near the southern Atlantic and Gulf of Mexico coasts (dry for cold Novembers), around the Great Lakes and in the Ohio River valley (dry, warm, January–February), in the southeastern United States (dry, warm, July–August), and across the northern Great Plains (dry, warm, November–January). Conversely, the regions confirmed to have essentially linear associations with traditional warm and cold events include the Gulf of Mexico coast (positive relation with eastern tropical Pacific, January–March), Ohio River valley (negative, central tropical Pacific, February), and mid-Atlantic coast (negative, eastern tropical Pacific, July–August). However, only nonlinear precipitation teleconnections are associated with SSTAs in tropical Pacific regions largely unrelated to ENSO. These principally involve anomalously dry conditions in much of the eastern half of the United States during January–March and in the central United States in July–October (warm SSTAs in west-central tropical Pacific horseshoe), and in a strip from Texas to New England in January and along the central gulf coast and lower Mississippi valley in April (warm SSTAs in far western tropical Pacific). The results thus demonstrate the sensitivity of central and eastern North American precipitation teleconnections to the location and extent of tropical Pacific SSTAs. In the appendix, the present results are also compared to the observed climate anomalies during the 1997–98 El Niño event.