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.

Biological and chemical consequences of the 1997–1998 El Niño in central California waters

“…Coastal upwelling continues but the waters recruited are low in nutrients, and productivity declines sharply. The coastal upwelling system of the northeast Pacific is also affected by El Niño, but the developmental sequence of events remains poorly described, and there is continued debate over the primary forcing (Norton & McLain, 1994;Simpson, 1984;Wooster & Fluharty, 1985).…”

Upper trophic level predators indicate interannual negative and positive anomalies in the California Current food web

“…An analysis by Norton & McLain (1994;see also Norton et al 1994) provides the basis for exploring the more remote factors that affect local ocean conditions and ultimately the food web of coastal central California. Using time-series analysis, these authors found significant correlation between water temperatures in the upper 300 m of the water column off California and 2 ocean-atmosphere systems: atmospheric pressure in Darwin, Australia, as part of the Southern Oscillation (SO), and pressure at 45"N, 165"W, as part of the Aleutian low (hereafter called the Aleutian low pressure system index, or AL), 1954 to 1986.…”

California cooperative oceanic fisheries investigations. Reports volume 37, January 1--December 31, 1995

“…Certainly anomalous warming and cooling patterns in the North Pacific result from complex interactions between atmospheric and oceanic processes in the tropics and extratropics. Norton and McClain (1994) conclude that warming episodes associated with equatorial forcing events are more likely to be detected at depth (>lo0 m), because of oceanic long waves, whereas warming associated with local forcing is more likely to be detected at the surface, and the most pervasive regional ocean warming effects during the fall-winter cooling season are associated with the equatorial atmosphere. Maximum warming (in the northern coastal Cahfornia Current) occurs in the fall-winter season following the tropical El Niiio initiated in the previous December through July.…”

“…Some aspects of this association are worth investigating further, including similarities in the life histories of these species, the effect of longwave propagation up the slope during strong ENSO events, the tendency for equatorial forcing to be felt more strongly at depth (Norton and McClain 1994), and transport of abundant large oceanic copepods shoreward (McFarlane and Beamish 1992).…”

“…The northeast Pacific sea-level, current, and near-surface temperature anomalies associated with El Niiio and La Niiia events provide some evidence of poleward-propagating coastal Kelvin waves and westward-propagating Rossby waves (e.g., Enfield and Allen 1980;Chelton and Davis 1982;Norton and McClain 1994; Gill 1982). The extratropical near-surface ocean temperature anomalies that are part of mechanism 2 may influence the development of the overlying extratropical atmospheric pressures and winds that are part of mechanism 1.…”