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Lerczak, JA, Winant CD, Hendershott MC.  2003.  Observations of the semidiurnal internal tide on the southern California slope and shelf. Journal of Geophysical Research-Oceans. 108   10.1029/2001jc001128   AbstractWebsite

[1] We give a detailed description of the semidiurnal-band current and temperature variability observed during the Internal Waves on the Continental Margin (IWAVES) field experiments of 1996 and 1997 off of Mission Beach, California. This variability was dominated by the internal tide, and the structure of the internal tide on the slope and shelfbreak region was different from that on the narrow shelf. On the slope and shelfbreak, the internal tide was dominated by alongshore propagating coastal-trapped waves. In this region, semidiurnal-band currents were predominantly oriented in the alongshore direction. In the lower half of the water column at a water depth H of 350 m, current and temperature variability were consonant with a short wavelength (similar to8 km) bottom trapped wave propagating in the alongshore direction to the north. In the upper 120 m of the water column (above the depth of the shelfbreak), slope and shelfbreak currents were highly coherent with a zero phase lag; that is, there was no phase propagation in the cross-shore direction. On the narrow (similar to10 km) shelf, cross-shore currents u were much more energetic than on the slope and had the structure of a mode-one internal wave. The alongshore currents v decreased monotonically from the surface to the bottom of the water column with a phase that did not change with depth. The near-bottom u signal propagated toward the coast during all mooring deployments, faster in the summer than in the fall. The near-bottom u and mid-column temperature relative phase was neither consistent with a purely progressive nor a purely standing mode-one internal wave. We conclude that the internal tide on the shelf was partially reflected.

Winant, CD, Dever EP, Hendershott MC.  2003.  Characteristic patterns of shelf circulation at the boundary between central and southern California. Journal of Geophysical Research-Oceans. 108   10.1029/2001jc001302   AbstractWebsite

[1] The coastal circulation in the Santa Barbara Channel (SBC) and the southern central California shelf is described in terms of three characteristic flow patterns. The upwelling pattern consists of a prevailing equatorward flow at the surface and at 45 m depth, except in the area immediately adjacent to the mainland coast in the SBC where the prevailing cyclonic circulation is strong enough to reverse the equatorward tendency and the flow is toward the west. In the surface convergent pattern, north of Point Conception, the surface flow is equatorward while the flow at 45 m depth is poleward. East of Point Conception, along the mainland coast, the flow is westward at all depths and there results a convergence at the surface between Point Conception and Point Arguello, with offshore transport over a distance on the order of 100 km. Beneath the surface layer the direction of the flow is consistently poleward. The relaxation pattern is almost the reverse of the upwelling pattern, with the exception that in the SBC the cyclonic circulation is such that the flow north of the Channel Islands remains eastward, although weak. The upwelling pattern is more likely to occur in March and April, after the spring transition, when the winds first become upwelling favorable and while the surface pressure is uniform. The surface convergent pattern tends to occur in summer, when the wind is still strong and persistently upwelling favorable, and the alongshore variable upwelling has build up alongshore surface pressure gradients. The relaxation pattern occurs in late fall and early winter, after the end of the period of persistent upwelling favorable winds.

Lerczak, JA, Hendershott MC, Winant CD.  2001.  Observations and modeling of coastal internal waves driven by a diurnal sea breeze. Journal of Geophysical Research-Oceans. 106:19715-19729.   10.1029/2001jc000811   AbstractWebsite

During the Internal Waves on the Continental Margin (IWAVES) field experiments of 1996 and 1997 off of Mission Beach, California (32.75 degreesN), we observed energetic, diurnal-band motions across the entire study site in water depths ranging from 15 to 500 m and spanning a cross-shore distance of 15 kin. The spectral peak of the currents was at the diurnal frequency (sigma (Di) = 1 cpd) and was sufficiently well resolved to be clearly separated from the slightly higher local inertial frequency (f = 1.08 cpd). These motions were surface enhanced and clockwise circularly polarized and had an upward phase propagation speed of similar to 68 m d(-1), suggesting that the motions were driven predominantly by the diurnal sea breeze. However, the downward energy (upward phase) propagation seems irreconcilable with the subinertial diurnal period, and moreover, the intermittent diurnal current events were not obviously associated with diurnal sea breeze events. We rationalize these features using a flat-bottomed linear modal sum internal wave model that includes advection and refraction due to subtidal alongshore flow, V(x, t). Fluctuations in V at the observing site can change the "effective" local Coriolis parameter f + V-x by as much as 50%, thus making the diurnal motions at different times effectively either subinertial or superinertial. The model is integrated numerically for 200 days at a latitude of 32.75 degreesN under different wind and subtidal flow conditions: purely diurnal winds and no V, purely diurnal winds and a time-independent V, narrow-band diurnal winds and no V, and narrow-band diurnal winds and subtidal, time-dependent V. Model diurnal currents forced by narrow-band diurnal winds and subtidal V show complex offshore structure with realistic intermittency and spectral broadening. This study suggests that continental margins in the vicinity of the 30 degrees latitude (where sigma (Di) = f) are regions that could potentially produce energetic, sea breeze-driven baroclinic motions and that these motions could be regulated by the vorticity of the local subtidal currents.

Dever, EP, Hendershott MC, Winant CD.  1998.  Statistical aspects of surface drifter observations of circulation in the Santa Barbara Channel. Journal of Geophysical Research-Oceans. 103:24781-24797.   10.1029/98jc02403   AbstractWebsite

Argos-tracked drifters are used to study the near-surface circulation in the Santa Barbara Channel. The mean consists of a cyclonic cell in the western Santa Barbara Channel with weaker flow in the eastern Channel. Drifter mean velocities agree well with record means from near-surface current meters. At the eastern entrance to the channel, drifter velocities are biased toward outflow (eastward velocity) conditions. Drifter variability at synoptic and seasonal scales shows a tendency for upwelling and eastward flow in spring, a strong cyclonic circulation in summer, poleward relaxation in fall, and weak, variable circulation in winter. Drifter estimates of eddy stress divergence indicate advective terms play a secondary role in the mean surface momentum balance. Lagrangian time and space scales are about 1 day and under 10 km, respectively. The mismatch between Lagrangian and Eulerian timescales indicates advective terms are important to the fluctuating circulation.