The seasonal and interannual variability of the California Current system: A numerical model

Abstract

A reduced gravity model that incorporates the geometry of western North America has been used to study the dynamics of the California Current system. Three experiments were performed: first the model was run using 19 years of wind stress from the Comprehensive Ocean‐Atmosphere Data Set (local model); a second experiment (remote model) consisted of forcing the model through its southern boundary using the results of a similar reduced gravity equatorial model; in a third experiment, both forcings were used simultaneously (local plus remote model). The main objective of this work was to analyze the low‐frequency variability on the California Current system in terms of its contributions from remote and local forcing. Away from the coast, the basic (steady) state of the model is determined by the predominantly negative wind curl through a Sverdrup balance. The general seasonal cycle is in agreement with what has been described by other authors. Through cross‐correlation and cross‐spectral analysis between the model results and observed sea level data, it was established that most of the interannual variability in sea level height at the coast is due to disturbances of equatorial origin that propagate into the region in the form of coastally trapped Kelvin waves. For the annual frequency variability, on the other hand, it was found that both local and remotely forced variability contribute to the total variance.

ENSO effects on primary production off Baja California

“…The waters that detach mainly during spring/summer upwelling (Parés-Sierra and O'Brien, 1989;Simpson, 1987, 1990;Hickey, 1993;Venrick, 2000) invade the offshore stations of these two lines, modifying the temporal and spatial distribution of oceanic production. This high primary productivity calculated for line 90 during the last two cold events (1995 and 1999) has been associated with high values of the sardine spawning biomass in the southern California Current, according to CalCOFI's Figura 6.…”

“…The warm phase was recorded in 1977 and continued until 1998, increased by the 1982-83, 1992-93 and 1997-98 ENSO events that affected the California Current region (Parés-Sierra and O'Brien, 1989;Smith, 1995;Hayward et al, 1999;Moser et al, 2001;Hernández-de la Torre et al, 2003;Peterson and Schwing, 2003). The mean P T value for the autumn/winter period in ENSO years increased before the event (-1), apparantly due to the greater occurrence of nutrients in the euphotic zone; it decreased in the key year (0) and increased up to two years after (+1, +2) during the six events recorded in the time series.…”

The relative influences of El Niño‐Southern Oscillation and Pacific Decadal Oscillation on paralytic shellfish toxin accumulation in northwest Pacific shellfish

“…During El Niñ o events, the coastal ocean of the Pacific Northwest is influenced by (i) coastally trapped waves that originate in the equatorial Pacific and propagate poleward along the west coast of the United States (Enfield and Allen 1980;Pares-Sierra and O'Brien 1989;Meyers et al 1998), (ii) enhanced poleward flows over the continental shelf and slope (Huyer and Smith 1985), and (iii) reduced coastal upwelling (Huyer et al 2002). These teleconnection patterns produce warmer than usual SSTs in the Pacific Northwest that persist for up to three seasons (Moore et al 2008a).…”

Leg 167 Introduction

“…California Current structure thus reflects both the local winds along the west coast of North America and basinwide events within the north and equatorial Pacific Ocean. The importance of both local and remote forcing in California Current flow has been emphasized by such modeling efforts as those of Pares-Sierra and O'Brien (1989), who found that the local wind field in the northeastern Pacific is adequate to drive the annual cycle of the current system and to create the general features of its structure. They could only model interannual variations of the California Current by coupling the local model with one driven by equatorial winds.…”

“…Warm years (1958,1959) are typified by weak equatorward transport. Most of the interannual variation is coupled to El Niño−Southern Oscillation (ENSO) events in the equatorial Pacific (Pares-Sierra and O'Brien, 1989).…”