INTERANNUAL AND INTERDECADAL VARIABILITY IN UNITED-STATES SURFACE-AIRTEMPERATURES, 1910-87

Monthly mean surface-air temperatures at 870 sites in the contiguous U nited States were analyzed for interannual and interdecadal variabilit y over the time interval 1910-87. The temperatures were analyzed spati ally by empirical-orthogonal-function analysis and temporally by singu lar-spectrum analysis (SSA). The dominant modes of spatio-temporal var iability are trends and nonperiodic variations with time scales longer than 15 years, decadal-scale oscillations with periods of roughly 7 a nd 10 years, and interannual oscillations of 2.2 and 3.3 years. Togeth er, these modes contribute about 18% of the slower-than-annual United States temperature variance. Two leading components roughly capture th e mean hemispheric temperature trend and represent a long-term warming , largest in the southwest, accompanied by cooling of the domain's sou theastern quadrant. The extremes of the 2.2-year interannual oscillati on characterize temperature differences between the Northeastern and S outhwestern States, whereas the 3.3-year cycle is present mostly in th e Western States. The 7- to 10-year oscillations are much less regular and persistent than the interannual oscillations and characterize tem perature differences between the western and interior sectors of the U nited States. These continental- or regional-scale temperature variati ons may be related to climatic variations with similar periodicities, either global or centered in other regions; such variations include qu asi-biennial oscillations over the tropical Pacific or North Atlantic and quasi-triennial oscillations of North Pacific sea-surface temperat ures.