Subtidal Eulerian currents in the upper and lower East River tidal strait: Spring 1981

Abstract

Subtidal Eulerian currents determined from long‐term current moorings in the East River tidal strait connecting the lower Hudson River with Long Island Sound show a well‐defined two‐layer circulation pattern within the eastern (upper) part of the East River. Mean surface currents flow toward the sound, and current at depth flows toward the Hudson. Within the western part of the East River, residual currents are vertically sheared, but flow is directed toward the sound at all depths, with stronger flow near the surface. Mean current magnitudes are of the order of 5 cm s−1. Results from frequency domain regression show that in the western (lower) portion of the strait, current fluctuations at frequencies of 0.25 cycles per day and higher are associated primarily with a barotropic response to fluctuations in hydraulic head. At lower frequencies, currents exhibit a baroclinic response to fluctuations in the discharge of the Hudson River. Within the upper part of the strait, currents respond to along channel winds. Response to fluctuations in sea level head and Hudson River discharge is detectable but not as well defined as within the lower East River. These results can provide insight into the relative importance of different forcing functions in maintaining the residual flow through the strait. The difference in the response characteristics of the western and eastern segments of the strait could be related to differences in the intensity of tidal mixing along the strait and the degree of water column stratification.