Sea Level Variability in Long Island Sound

Abstract

Sea level variability in Long Island Sound is examined at both tidal and subtidal frequencies over a 1-yr period. The sound is found to be decoupled effectively from the lower Hudson Estuary at tidal frequencies. The predominantly semidiurnal tides in the sound are forced by the oceanic tides transmitted from the mouth. There is a near fourfold amplification of the semi-diurnal tides within the sound due to resonance. Diurnal tides are much weaker in the sound, and there is also no evidence of significant amplification in the interior. At subtidal frequencies, the pressure-adjusted sea level in the interior of the sound is forced by a combination of co-oscillation with coastal sea level at the mouth and direct setup induced by local wind forcing over the surface of the sound. Because the longitudinal axis of Long Island Sound is roughly aligned with the open coast from Montauk Point to Sandy Hook, these two mechanisms work in concert to produce larger subtidal sea level fluctuations in the western sound relative to those in the eastern sound. A linearized, frequency-dependent analytical model is developed to aid the interpretation of field observations.