[1] Dye release experiments were performed together with microstructure profiling to compare the two methods of estimating diapycnal diffusivity during summer and fall stratification on the continental shelf south of New England. The experiments were done in 1996 and 1997 as part of the Coastal Mixing and Optics Experiment. During the 100 hours or so of the experiments the area of the dye patches grew from less than 1 km 2 to more than 50 km 2 [Sundermeyer and Ledwell, 2001]. Diapycnal diffusivities inferred from dye dispersion range from 10 À6 to 10 À5 m 2 /s at buoyancy frequencies from 9 to 28 cycles/hour. Diffusivities estimated from the dye and those estimated from dissipation rates in the companion paper by Oakey and Greenan [2004] agree closely in most cases. Estimates of diffusivities from towed conductivity microstructure measurements made during the cruises by Duda and Rehmann [2002] and Rehmann and Duda [2000] are fairly consistent with the dye diffusivities. The dye diffusivities would be predicted well by an empirical formula involving shear and stratification statistics developed by MacKinnon and Gregg [2003] from profiling microstructure measurements obtained at the same site in August 1996. All of the measurements support the general conclusion that the diffusivity, averaged over several days, is seldom greater than 10 À5 m 2 /s in the stratified waters at the site, and usually not much greater than 10 À6 m 2 /s. Severe storms, such as a hurricane that passed over the CMO site in 1996, can dramatically increase the mixing at the site, however.
[1] The characteristics of the principal barotropic diurnal and semidiurnal tides are examined for the South Atlantic Bight (SAB) of the eastern United States coast. We combine recent observations from pressure gauges and ADCPs on fixed platforms and additional short-term deployments off the Georgia and South Carolina coasts together with National Ocean Service coastal tidal elevation harmonics. These data have shed light on the regional tidal propagation, particularly off the Georgia/South Carolina coast, which is perforated by a dense estuary/tidal inlet complex (ETIC). We have computed tidal solutions for the western North Atlantic Ocean on two model domains. One includes a first-order representation of the ETIC in the SAB, and the other does not include the ETIC. We find that the ETIC is highly dissipative and affects the regional energy balance of the semidiurnal tides. Nearshore, inner, and midshelf model skill at semidiurnal frequencies is sensitive to the inclusion of the ETIC. The numerical solution that includes the ETIC shows significantly improved skill compared to the solution that does not include the ETIC. For the M 2 constituent, the largest tidal frequency in the SAB, overall amplitude and phase error is reduced from 0.25 m to 0.03 m and 13.8°to 2.8°for coastal observation stations. Similar improvement is shown for midshelf stations. Diurnal tides are relatively unaffected by the ETIC.
[1] Monthly circulation of the South Atlantic Bight is diagnosed using a 3-D, shallow water, finite element model forced with monthly wind stress and hydrographic climatology. Temperature and salinity observations from the period 1950-1999 are objectively interpolated onto the model domain, and Comprehensive Ocean-Atmosphere Data Set (COADS) wind velocities from 1975-1999 are used to prescribe the model surface wind stress. The resulting monthly temperature and salinity fields compare favorably to existing shelf climatology. River discharge maxima are evident in the spring temperature and salinity fields, and the rapid heating and cooling of the shelf are captured. The diagnostic circulation is largely wind-driven in the inner and mid-shelf, and the Gulf Stream is apparent in the solutions on the outer shelf. We present the monthly fields, including the temporal and spatial distribution of available hydrographic data, the regional COADS data that provide surface wind stress forcing, the objective analysis, and the model response to these forcings. The hydrographic and velocity fields provide best-priorestimates of the circulation for data assimilation studies in the region, as well as initial conditions for process-oriented prognostic model studies in the Georgia coastal region.
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