Data assimilation model study of wind effects in the Santa Barbara Channel

[1] Moored observations and numerical model results are used to describe the circulation during 1998 in Santa Maria Basin (SMB) and Santa Barbara Channel (SBC), located to the northwest and southeast, respectively, of a bend in the southern California coastline. Singular value decomposition (SVD) analysis of observed wind stress and currents yields a first mode that represents large-scale alongshore flow variability that appears to be wind driven, and a second mode which mostly represents flow variability in SBC and appears coherent with wind stress shear there. A three-dimensional numerical ocean circulation model is used to simulate the flow. The model-derived surface heat flux is most similar to observation-derived values in summer and least similar in winter, and more similar in SMB than in SBC. Empirical orthogonal function (EOF) analysis of the Coriolis and pressure gradient terms for modeled near-surface currents supports the hypothesis that the large-scale flow variability of the first mode is wind-driven. It further suggests that an alongshore pressure gradient drives the poleward flow along SBC's northern shelf. Wind stress curl (of which the shear along SBC is a part) or its gradient may govern such a pressure gradient, although this could not be ascertained. Modeled and observed currents are similar in their directions, but both the annual mean and variance tend to be smaller for modeled flow. SVD analysis shows that modeled and observed flows have similar modes of variability. Remotely driven flow may play a role in SMB, especially in summer.

Section: Introductionsupporting

confidence: 91%

Section: Numerical Model Simulationsmentioning

confidence: 99%

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Circulation in the Santa Maria Basin, California, during 1998

Ohashi

Wang

2004

“…Owing to this transitional location, the circulation of the SBC and its relationship with the California Current System has been studied in great depth. [e.g., Lynn and Simpson , 1987; Winant et al , 2003; Harms and Winant , 1998; Chen and Wang , 2000; Breaker et al , 2003; Oey et al , 2001], revealing a complex system of wind‐ and geostrophy‐driven circulation states. Typically along the coast of California to the north of the SBC, equatorward winds drive Ekman transport over the continental shelf, supporting strong upwelling conditions for much of the spring and summer [ Winant et al , 1987, 2003].…”

Section: Introductionmentioning

confidence: 99%

Controls on temporal patterns in phytoplankton community structure in the Santa Barbara Channel, California

Anderson¹,

Siegel²,

Brzezinski³

et al. 2008

Characterizing phytoplankton succession in the context of physical and chemical processes is important for understanding the mechanisms driving phytoplankton species composition and succession. An understanding of these processes ultimately influences the ability to predict the contribution of phytoplankton to carbon cycling, the initiation and persistence of harmful algal blooms, and the ability to use satellites for the remote sensing of specific phytoplankton taxa important for biogeochemistry. A statistical analysis of 5 years (1998−2003) of phytoplankton pigment concentrations from the Santa Barbara Channel using empirical orthogonal functions reveals four dominant modes of variability that explain 80% of the variance in the pigment data set. The annual cycle is characterized by a switching from a mixed‐phytoplankton assemblage mode to modes dominated by either diatoms, dinoflagellates, or a combination of nano‐ and pico‐phytoplankton. The dominant two modes correspond to a prebloom condition that precedes upwelling conditions, with all identified phytoplankton groups present in low abundance and a diatom‐dominated upwelling state that develops following spring upwelling. In 2001, the EOF analysis indicated a transition toward more intense diatom blooms in spring and summer and fewer, large dinoflagellate blooms. This trend was corroborated by analyses of diagnostic pigments and CHEMTAX analysis and may be linked to an increase in local upwelling intensity between 2001 and 2003. Both spring diatom blooms occurring after 2001 were dominated by toxic Pseudo‐nitzschia species and led to significant marine mammal deaths in the channel in 2003.

“…As part of the SBC‐SMB Circulation Study, numerical models were extensively used in simulating the observed seasonal flow patterns. Chen and Wang [1999, 2000] and Oey et al [2004] assimilated the temperature observations and made detailed validation of model currents with the observations in SBC. Ohashi and Wang [2004] did similar study but for SMB.…”

Section: Introductionmentioning

confidence: 99%

Impact of open ocean influence on a coastal model: The 1997–1998 El Niño off central California

Wang

Ohashi

2006

Self Cite

Extensive moored current meters, atmospheric observations, and hydrographic surveys were obtained off central California during the 1997–1998 El Niño. In this study the temperature observations from current meter moorings and hydrographic surveys are assimilated into a coastal ocean model to study the seasonal circulation in the Santa Barbara Channel–Santa Maria Basin (SBC‐SMB). Mean coastal circulation was dominated by a poleward jet in fall 1997 at the peak of the El Niño but returned to the normal surface convergent pattern in fall 1998. The data‐assimilated model reproduces well the observed flow patterns in both years. The interannual flow variability is examined through sensitivity analysis of the effects of local forcing and open ocean influence. It is shown that the poleward jet is associated with enhanced California Countercurrent during El Niño, while the surface convergence is driven by local wind stress curl. Taking advantage of the extensive data set, the climatology is compared with the synoptic states. It is found that the climatology could cause significant negative impact.