4.3
Coastal Observing Systems as tools for Impact Assessment and Emergency Response: The Santa Barbara Channel - Santa Maria Basin Study
Clinton D. Winant, SIO/Univ. of California, La Jolla, CA
The need to anticipate the potential impact of oil exploration and production activities on coastal resources, and the information needs of agencies charged with responding to coastal emergencies motivated the development of the oil-spill response system for the Santa Barbara Channel (SBC) and the Santa Maria Basin (SMB), along the California coast, between Ventura and Morro Bay.
As a first step toward developing this capability, the circulation was described in both areas based on an integrated observational and modeling program. Observations were gathered using three principal methods. Fixed station observations, using moored platforms in various depths provided temporally intensive measurements of the flow and associated physical parameters at 23 sites. The measurements were maintained for three years in the SBC and four years (including the 1997-98 El Nino event) in the SMB. Four long-term moorings were deployed for the entire period, and are currently still operational. Ship-borne surveys of water mass properties and current profiles provided spatially well-resolved maps of the circulation at the times when cruises were scheduled to service the moored array (about every 8 months). Lagrangian observations, using drifters drogued 1 meter below the surface documented the possible trajectories of surface water parcels released at different locations in different seasons. In all over 500 drifter trajectories were acquired. Positions were sampled on average every six hours, and the drifters were tracked for a maximum of 40 days.
In the Santa Barbara Channel (SBC), the moorings and trajectories document a persistent cyclonic circulation with a typical re-circulation period between three and five days. In the spring currents near the mainland are weaker than near the Channel Islands and the overall flow is toward the southeast. Trajectories document the possibility for water parcels to leave the channel through the inter-island passes. In the late fall and winter, a poleward flow with velocities often exceeding 0.5 m/s is confined within 20 km of the mainland. Between these two seasons, the cyclonic tendency is enhanced although most of the drifters eventually migrate westward. The trajectories of drifters released at the same time from sites only 20 km apart can be remarkably different.
In the Santa Maria Basin (SMB), the direction and amplitude of the flow is strongly depth dependent. Near the surface, moorings and drifters show the flow to be equatorward except during late fall and early winter when the surface flow is poleward. Beneath the surface layer the flow is poleward except in March and April, right after the spring transition.
The observations provided a basis on which several data assimilating models of the circulation are based. The models reproduce all the major observed features of the circulation, including individual drifter trajectories. With little effort these models could be used to maintain an operational predictive capability with real predictive skills over periods of a few days.
Session 4, Research Systems
Tuesday, 11 February 2003, 12:45 PM-2:00 PM
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