Seasonal Climatic Anomaly Types for the North Pacific Sector and Western North America

Abstract

Recurrent patterns of seasonal sea level pressure anomaly over the North Pacific sector and western North America are objectively identified using correlation coefficients between anomaly maps as a pattern recognition device. Five major anomaly type patterns are identified for each season. Each pressure anomaly type pattern is briefly discussed in terms of atmospheric circulation features and associated anomaly patterns of temperature and precipitation over the contiguous United States. Occurrences of each type pattern are analyzed in the time domain. Spring and summer types featuring below-normal pressures at high latitudes, associated with warm, dry conditions in the United States, occurred relatively often during the period of warm Northern Hemisphere temperatures from the mid-1920's to the mid-1950's. Types featuring above-normal pressure over high-latitude land area tended to occur frequently for all seasons during the period of relatively cool Northern Hemisphere temperatures prior to 1920. This study is useful for investigating variations in the nature or frequency of certain types of large-scale atmospheric circulation features in relation to global-scale temperature trends.