Climatic variability of the circulation in the Rhode Island Sound: A modeling study

Yiyong Luo,Shuwen Zhang,Lew Rothstein,Qianqian Liu

doi:10.1002/jgrc.20285

Yiyong Luo, Shuwen Zhang + Show 2 more

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https://doi.org/10.1002/jgrc.20285

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Abstract

Seasonal and interannual variability of the circulation in the Rhode Island Sound (RIS) is investigated by employing the Regional Ocean Modeling System (ROMS) with two configurations in which a local‐scale model with very fine resolution over the RIS is nested within a regional‐scale model covering the entire US Northeastern Continental Shelf. The models are driven by tidal harmonics, climatological river discharge, and realistic ocean open boundary conditions and atmospheric forcing from January 2004 to December 2009. Results show that the tidal residual current forms a cyclonic circulation in the RIS, with amplitude of a few centimeters per second. During summer, the cyclonic circulation is significantly strengthened owing to tidal mixing and local stratification. However, due to strong northwesterly winds in winter, the cyclonic circulation disappears and instead the surface currents in the RIS move offshore. Simulations further indicate that the RIS winter currents, in terms of their magnitude and direction, have interannual variability that appears to be related to the North Atlantic Oscillation (NAO) winter index. In addition, the southwestward jet near the southern New England shelf break is found to intensify (weaken) during the low (high) phases of the NAO with a lag of about 1 year. The ROMS models are also used to examine the response of the regional ocean circulation to global warming, with both atmospheric forcing and open boundary conditions obtained from global climate model outputs. As the climate warms, it is found that the cyclonic gyre in the RIS is intensified, and this change is due to an intensification of the larger‐scale cyclonic coastal ocean circulation over the Middle Atlantic Bight in a warming climate.

Highlights

A localscale Regional Ocean Modeling System (ROMS) is configured for the domain including the Rhode Island Sound (RIS), the Block Island Sound (BIS), the Long Island Sound (LIS) and the adjacent inner shelf area, with a horizontal grid varying from 600 m over the RIS and BIS to 1 km along the boundaries
[36] we focus on how the circulation over the southern New England shelf as well as the RIS responds to associated changes in surface forcing during 2004–2009
As the climate warms (Figure 20b), it is found that the modeled changes in the regional ocean circulation exhibit a spatial pattern that is suggestive of more negative North Atlantic Oscillation (NAO)-like conditions such as a strengthening or expanding of the cyclonic circulation in the Gulf of Maine, a speedup of the anticyclonic circulation around the Georges Bank, an intensification of the southwestward currents over the southern New England shelf and slope, and a weakening or a southward movement of the Gulf Stream (GS)

Summary

Introduction

[2] The Rhode Island Sound (RIS) is a semicircular embayment off the Southern Rhode Island and Massachusetts coast (Figure 1). Driven primarily by an alongshore pressure gradient associated with the largescale wind stress and heat flux patterns over the region, this southwestward flow may be viewed as a boundary-layer component of the large-scale ocean general circulation of the western North Atlantic Based upon this point of view, the observed flow in the RIS might plausibly be decomposed into a mean component driven by remote forcing and a fluctuating component driven by local forcing. Long-term data collected in Narragansett Bay have revealed trends of increasing water temperature, in winter, and in the past 25 years winter water temperatures have increased by approximately 2C [e.g., Nixon et al, 2004] Accompanying this warming may be a change in the circulation pattern of the southern New England shelf.

Design of Numerical Experiments

Motivation

Summary