The Pacific/North American Teleconnection Pattern and United States Climate. Part II: Temporal Characteristics and Index Specification

Abstract

The PNA teleconnection index, a measure of the strength and phase of the Pacific/North American teleconnection pattern, is used to examine changes in the midtropospheric flow over North America on decadal, interannual, and intra-annual time scales. The index corroborates previous findings that a major change in the midtropospheric circulation took place over North America during the late 1950s. The time series of index values also demonstrates the existence of a previously unknown quasi periodicity in the configuration of midtropospheric heights over the North American sector. A seasonal specification analysis is conducted to identify climate system components that are closely linked to the PNA teleconnection. The selection of predictor variables is based on recent modeling and observational work suggesting their probable involvement with midiatitude flow variations. These include sea surface temperatures for locations in the tropical Pacific and North Pacific, along with Asian land surface temperatures and upper-level pressure gradients associated with the East Asian jet. Results suggest that the response of the midtropospheric flow over North America to these variables has a seasonal dependence consistent with theoretical studies. In winter months the explained variance is relatively high, with both tropical and midlatitude variables influencing the specification equations. During spring, the explained variance reaches a maximum, with only midiatitude variables having significant association with PNA index variations. The summer and autumn seasons show no significant association between Pacific basin variables and PNA index variations.