Analysis of flow within the coastal boundary layer off Long Island, New York

Abstract

From 1974 through 1978 a series of intensive measurements were made in the coastal waters within 12 km of Long Island. The data were derived from two sources: a mooring array from which time series of temperature, salinity and water velocity were measured at four depths at each of four offshore distances; and high resolution, daily hydrographic surveys. Analysis of subtidal cross-shore velocity fluctuations has indicated a two-layer response to wind forcing, with near-surface flow to the right of the longshore wind and opposing flow below. The magnitude of these fluctuations increased in the seaward direction on a scale nearly equal to the internal deformation radius. The phase between longshore velocity fluctuations and longshore wind stress approached zero with decreasing bottom depth, probably the result of bottom stress. The vertical structure of longshore fluctuations during stratified conditions markedly differed from that during unstratified conditions, and resembled the structure derived from a simple two-layer coastal flow model. Significant mean offshore flow was measured during experiments in August and September, despite negligible mean wind stress during the same periods. This flow was most likely due to persistent longshore density gradients, as are consistently inferred from hydrographic data taken in the vicinity.