The California Current system: The seasonal variability of its physical characteristics

Abstract

The seasonal variation of the physical characteristics and of large-scale current patterns of the California Current system is examined using harmonic analysis applied to the 23 years of California Cooperative Oceanic Fisheries Investigations data collected between 1950 and 1978. The amplitude and phasing of seasonal variation in dynamic height and the overall standard deviation of dynamic height define three domains: oceanic, coastal, and an intervening transition zone. The transition zone is a broad band centered approximately 200-300 km offshore and parallel to the coast in which the seasonal range of dynamic height is a relative minimum and the standard deviation is a maximum. It is hypothesized that recurrent mesoscale eddies and energetic meanders create this zone. Such eddies and meanders would contribute heavily to the standard deviation of dynamic height but not its seasonal variation. The transition zone is coincident with the core of flow of the California Current. A strong interaction between the core of the California Current and the mesoscale eddy field is evident. Seasonal variation in the fields of temperature, salinity, {rt, and oxygen is related to variations in the California Current, the Inshore Countercurrent and the California Undercurrent through vertical adjustments in the density field and through changes in transport. In the undercurrent there is an especially strong relation between seasonal variations in strength of flow and the extreme values of water mass characteristics.

Lagrangian flow in the California Undercurrent, an observation and model comparison

“…For clarity and lack of data we have called the subsurface poleward flow the California Undercurrent throughout. Further observations are needed to clarify whether the periods Ž of strengthening poleward flow to the surface Lynn and Simpson, 1987;Hickey, 1998;Reid and . Schwartzlose, 1962 represent the merging of two flows, e.g.…”

“…tered at about 1238W at the latitude of Monterey Ž . Lynn and Simpson, 1987;Schwing et al, 1991 . Poleward flow is also observed over the upper slope during much of the year and is strongest during March-August. This system of currents is also affected by longer period variation such as interannual Ž El Nino events the latest occurring in 1991-1992 .…”

A time series study of silica production and flux in an eastern boundary region: Santa Barbara Basin, California

“…However, six synoptic states of circulation have been described, only two of which include this gyre [Harms and •'nant, 1998]. Physical effects of large scale climatic forcing such as E1 Nifio conditions in the eastern tropical Pacific Ocean have a strong influence on the California Current system, including anomalous surface water warming [Bernal, 1981;Lynn and Simpson, 1987]. Palaeoceanographic studies indicate that the SBB is sensitive to climate change, which is recorded in the sediment record (see review by Schimmelmann and Lange [1996]).…”

Seasonal climatology of hydrographic conditions in the upwelling region off northern Chile

“…As an example, the California Cooperative Fisheries Investigation (CalCOFI) time series of physical and biological measurements in the southern part of the California Current has made possible the quantification of variability on a range of timescales. These include the seasonal cycles of cnrrents and water properties [Chelton, 1984;Lynn and Simpson, 1987], interannual variability in currents, water masses, and zooplankton volumes [Chelton et al, 1982] and provides a baseline against which to calculate anomalies and a poleward undercurrent next to the continental slope from 15 ø to quantify future changes. 40øS carrying salty water with extremely low oxygen Few of the previous studies of this overall region include concentrations to the south.…”