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Peng Cheng
,
Robert E. Wilson
,
Robert J. Chant
,
David C. Fugate
, and
Roger D. Flood

Abstract

The dynamics of lateral circulation in the Passaic River estuary is examined in this modeling study. The pattern of lateral circulation varies significantly over a tidal cycle as a result of the temporal variation of stratification induced by tidal straining. During highly stratified ebb tides, the lateral circulation exhibits a vertical two-cell structure. Strong stratification suppresses vertical mixing in the deep channel, whereas the shoal above the halocline remains relatively well mixed. As a result, in the upper layer, the lateral asymmetry of vertical mixing produces denser water on the shoal and fresher water over the thalweg. This density gradient drives a circulation with surface currents directed toward the shoal, and the currents at the base of the pycnocline are directed toward the thalweg. In the lower layer, the lateral circulation tends to reduce the tilting of isopycnals and gradually diminishes at the end of the ebb tide. A lateral baroclinic pressure gradient is a dominant driving force for lateral circulation during stratified ebb tides and is generated by differential diffusion that indicates a lateral asymmetry in vertical mixing. Over the thalweg, vertical mixing is strong during the flood and weak during the ebb. Over the shoal, the tidally periodical stratification shows an opposite cycle of that at the thalweg. Lateral straining tends to enhance stratification during flood tides and vertical diffusion maintains the relatively well-mixed water column over the shoal during the stratified ebb tides.

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New York City's Vulnerability to Coastal Flooding

Storm Surge Modeling of Past Cyclones

Brian A. Colle
,
Frank Buonaiuto
,
Malcolm J. Bowman
,
Robert E. Wilson
,
Roger Flood
,
Robert Hunter
,
Alexander Mintz
, and
Douglas Hill

New York City, New York (NYC), is extremely vulnerable to coastal flooding; thus, verification and improvements in storm surge models are needed in order to protect both life and property. This paper highlights the Stony Brook Storm Surge (SBSS) modeling system. It utilizes surface winds and sea level pressures from the fifth-generation Pennsylvania State University (PSU)-National Center for Atmospheric Research (NCAR) Mesoscale Model (MM5) or the Weather Research and Forecasting (WRF) model to drive the Advanced Circulation Model for Coastal Ocean Hydrodynamics (ADCIRC). For this study, the MM5 is utilized at 12-km grid spacing and ADCIRC is run on an unstructured grid down to ~10-m resolution in areas around Long Island and NYC.

This paper describes the SBSS and its performance across the NYC region during the 11–12 December 1992 nor'easter and Tropical Storm Floyd on 16–17 September 1999. During the 1992 event, east-northeasterly surface winds of 15–25 m s−1 (30–50 kts) persisted for nearly 24 h, while hurricane-force winds (35–40 m s−1) occurred for a few hours just south of western Long Island. This created a 1.0–1.5-m storm surge around NYC and western Long Island Sound over three tidal cycles. ADCIRC successfully simulated the peak water levels to within ~10%, and it realistically simulated some of the flooding across lower Manhattan. The surface winds for Tropical Storm Floyd were only 5–10 m s−1 weaker than the 1992 event, but no coastal flooding occurred during Floyd, because the storm approached during a low tide. Additional Floyd simulations were completed by shifting the storm's landfall to the spring high tide the previous week, and by doubling the wind speed to mimic a category-1 hurricane. A combination of the spring high tide and a category-1 hurricane scenario during Floyd would have resulted in moderate flooding at several locations around NYC.

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