Characteristic patterns of buoyant flows in the Block Island Sound: Data analysis and numerical simulation

The surface coastal circulation in and off the Block Island Sound (BIS) is examined based on one-year HF radar (CODAR) observations, bottom-mounted Acoustic Doppler Current Profiler (ADCP) moorings, and a three-dimensional, primitive-equation model to characterize the buoyant flow patterns and their temporal evolution.; The surface flow patterns in BIS are determined from one-year CODAR observations and their temporal evolution is examined. Three analysis methods, visual sorting, Self-Organizing Maps (SOM) and Empirical Orthogonal Functions (EOF), are used and their results are compared. The study shows that the SOM analysis nicely complements the traditional EOF analysis, and both are consistent with the visual sorting. A synoptic description of the surface circulation is presented in terms of three characteristic patterns in spring/summer (April to September) and four characteristic patterns in fall/winter (January to March and October to December). The characteristic flow patterns are mainly determined by the wind and seasonal Long Island Sound (LIS) outflows. In spring and summer, a southwestward coastal mean flow is strong, and the wind is generally insignificant. In fall and winter, on the other hand, the coastal mean flow is weak, and the flow is mostly forced by synoptic storms.; The Princeton Ocean Model (POM) is applied to study the three-dimensional barotropic semidiurnal tidal response in the New York Bight (NYB) and Block Island Sound (BIS). The model is driven at the open boundary with specified tidal transports. Model tidal sea levels and current ellipses are verified with the coastal sea levels, historical moored bottom pressure and current meter observations, and moored ADCP observations. The model results generally show very good agreement with the observations. The model results also are used to evaluate the CODAR data quality by comparing the total and radial tidal current ellipses. While the CODAR measurements generally are of high quality, the data at the mouth of Long Island Sound seems less reliable.; POM also is used to simulate the coastal buoyant flows for a one-year (2001) period. The external forcing includes the LIS outflows, ambient coastal currents, semidiurnal tides, and local winds. Model results are compared with the CODAR and ADCP observations. The agreement in the low-frequency current fluctuations is very good. Consistent with the data analysis, model results indicate that the wind and seasonal LIS outflows are the dominant factors on coastal buoyant outflows. On the other hand, the model predicts a persistent (mean) headland tidal residual eddy south of Montauk Point, which is not supported by the ADCP and CODAR observations. This suggests that small-scale lateral dissipation which is not explicitly treated in the model may be important.; This work represents the first comprehensive model and observation comparisons of the coastal buoyant outflows for an entire seasonal cycle. The success of our study is a major step towards developing a model-observational based coastal observatory system.