Properties of Flow within the Coastal Boundary Layer off Long Island, New York

Abstract

Properties of flow within the nearshore waters off the southern coast of Long Island are established by statistical analysis of data from a moored current meter array and by concurrent hydrographic information. Upwelling-downwelling episodes dominate subdiurnal frequency fluctuations of the flow within a coastal boundary layer of about 10 km width. The structure of the boundary layer appears to be baroclinic during the presence of a pycnocline, and is also influenced by frictional effects because of the increase of bottom depth with distance from shore. Significant mean offshore flow is evidenced by measurements taken in autumn and late summer, despite negligible mean wind stress during the same periods. This flow is most likely related to the large longshore density gradients which are consistently inferred from hydrographic data taken in the vicinity. During events of roughly constant wind heading, the cross-shore flow of a particular direction is often confined within a distinct density band. This has made it possible to infer cross-shore flow which was otherwise unresolved by the current meter array.