Modeling the tide and wind-induced circulation in Buzzards Bay

Abstract

Hydrodynamic model application to Buzzards Bay is performed using a three-dimensional Boundary-fitted Hydrodynamic model in this study. The model is forced with observed tidal harmonic constants along the open boundaries and winds on the surface. The main focus of the present study is to model the detailed wind and tide-induced circulation in Buzzards Bay. The observed surface elevations and currents given in [Butman, B., Signell, R., Shoukimas, P., Beardsley, R.C., 1988. Current Observations in Buzzards Bay, 1982–1986. Open File Report 88-5. United States Geological Survey] and the tide and current harmonics given in [Signell, R.P., 1987. Tide- and Wind-forced Currents in Buzzards Bay, Massachusetts. Technical Report WH-87-15. Woods Hole Oceanographic Institution, Woods Hole, Massachusetts] are used to validate the model predictions. The calibrated model is then used to study the relative contributions of tidal and wind forcing on the instantaneous and residual circulation in Buzzards Bay. The amplitudes and phases of the principal tidal constituents at 10 tidal stations in Buzzards Bay obtained from a harmonic analysis of a 60-day simulation compare well with the observed data. The predicted amplitude and phase of the M 2 tidal constituent of surface elevations at these stations are, respectively, within 4 cm and 5° of the observed data. The errors in the model-predicted M 2 harmonic principal current speeds are less than 6 cm/s, and the principal current directions and phases are within 14° of the observations. The observed surface elevations and currents given in [Butman, B., Signell, R., Shoukimas, P., Beardsley, R.C., 1988. Current Observations in Buzzards Bay, 1982–1986. Open File Report 88-5. United States Geological Survey] are used to validate the model-predicted low-frequency surface elevations and currents. The model predictions in low-frequency surface elevations at Woods Hole closely follow the trends seen in the observations with a correlation coefficient of 0.735, but fail to capture some of the peak surges seen in the observations. The model-predicted low-frequency currents in the east–west direction at stations in Buzzards Bay compare well with the observations with the correlation coefficient exceeding 0.811 and the model capturing the trends seen in the observations, for the most part. However, the model-predicted north–south velocities does not compare well with the observations. The model-predictions agree with the observations that the tidal currents in Vineyard Sound lagged the currents in Buzzards Bay by more than 3 h. The interaction of wind stress with large bathymetric gradients was shown to cause many vortices in Buzzards Bay, as seen from the model predictions. Model simulations show that the winds play a more dominant role than the tides in the generation of the barotropic residual currents in Buzzards Bay, while the model-predicted tide-induced residual current was seen to be small.