Diagnostic patterns of seasonal and interannual temperature variation off the west coast of the United States: Local and remote large‐scale atmospheric forcing

Abstract

Remote forcing from the equatorial Pacific and local forcing from the North Pacific lead to interannual ocean temperature change along the west coast of the United States. In fall‐winter seasons, coherent temperature changes extending from the surface to 300 m depth indicate remote forcing. Correlations between time series of ocean temperature change and series of equatorial sea level pressure (SLP) at 12.4°S × 130.9°E were as great below 100 m as at the surface. From 1954 to 1986, coherent warming events occurred only during moderate to strong El Niño years. Warming events more closely related to local North Pacific SLP at 45°N × 165°W have correlations which were greatest at the ocean surface. The first three empirical orthogonal functions (EOFs) derived from ocean temperature change series at 0, 100, 200, and 300 m accounted for more than 98% of the variance. The first EOF is most closely correlated with remote forcing, and the second and third EOFs are closely correlated to local forcing. At the sea surface, lags of up to 6 months were found for remote forcing, while lags of less than 3 months were characteristic of local forcing. At 300 m there was an additional oceanic response which appears in phase with remote forcing. The study shows that interannual warming off the west coast has two distinguishable geographical origins and that the remotely generated warming signal arrives as complex dynamic structure having apparent propagation rates from 30 to greater than 200 km/d.