The Origin of Along-Shelf Pressure Gradient in the Middle Atlantic Bight

Xu, Fanghua; Oey, Lie Yauw

doi:10.1175/2011jpo4589.1

Cited by 41 publications

(45 citation statements)

References 75 publications

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“…This sea level gradient is consistent with the value estimated by Xu and Oey (2011), which reported a slope of 4.8 × 10 −8 with a range of 10 −7 , and is also consistent with the estimate by Zhang et al (2011), which is 0.2-2.5 × 10 −7 . It is equivalent to a 0.36 m mean sea level difference over the 1600 km distance from the Nova Scotia shelf to the North Carolina shelf, arguably contributing to the equatorward mean shelf circulation.…”

Section: Mean Dynamical Balances Along the 200 M Isobathsupporting

confidence: 89%

“…While the results suggest the important roles of along-shelf pressure gradient and bottom stress, direct measurements are very difficult to achieve due to large observational uncertainties. In an effort to understand the origin of the along-shelf pressure gradient (ASPG) in the MAB, Xu and Oey (2011) estimated the mean ASPG is about 5-8 × 10 −8 in the MAB. They also suggested that river and coastal Labrador sea waters transport contribute to the positive mean along-shelf pressure gradient (ASPG, tilting up northward), whereas wind and Gulf Stream tend to produce a negative mean ASPG.…”

Section: Introductionmentioning

confidence: 99%

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Mean circulation in the coastal ocean off northeastern North America from a regional-scale ocean model

Chen

2015

Ocean Sci.

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Abstract. A regional-scale ocean model was used to hindcast the coastal circulation over the Middle Atlantic Bight (MAB) and Gulf of Maine (GOM) from 2004 to 2013. The model was nested inside a data assimilative global ocean model that provided initial and open boundary conditions. Realistic atmospheric forcing, tides and observed river runoff were also used to drive the model. Hindcast solutions were compared against observations, which included coastal sea levels, satellite altimetry sea surface height, in situ temperature and salinity measurements in the GOM, and observed mean depth-averaged velocities. Good agreements with observations suggest that the hindcast model is capable of capturing the major circulation variability in the MAB and GOM. Time-and space-continuous hindcast fields were used to depict the mean circulation, along-and cross-shelf transport and the associated momentum balances. The hindcast confirms the presence of the equatorward mean shelf circulation, which varies from 2.33 Sv over the Scotian Shelf to 0.22 Sv near Cape Hatteras. Using the 200 m isobath as the shelf/slope boundary, the mean cross-shelf transport calculations indicate that the shelfbreak segments off the Gulf of Maine (including the southern flank of Georges Bank and the Northeast Channel) and Cape Hatteras are the major sites for shelf water export. The momentum analysis reveals that the along-shelf sea level difference from Nova Scotia to Cape Hatteras is about 0.36 m. The nonlinear advection, stress, and horizontal viscosity terms all contribute to the ageostrophic circulation in the along-isobath direction, whereas the nonlinear advection plays a dominant role in determining the ageostrophic current in the cross-isobath direction.

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Section: Mean Dynamical Balances Along the 200 M Isobathsupporting

confidence: 89%

Section: Introductionmentioning

confidence: 99%

Mean circulation in the coastal ocean off northeastern North America from a regional-scale ocean model

Chen

2015

Ocean Sci.

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“…Steady alongshore coastal currents can be induced in a balance of surface and bottom stresses in the direction of wind stress [e.g., Allen and Smith, 1981;Lentz and Winant, 1986]. Offshore forcing associated with boundary currents imposes cross-shore and alongshore pressure gradients on the shelf driving coastal currents to flow, in general, the same direction as the boundary currents [Palma et al, 2008;Xu and Oey, 2011;Wood et al, 2016]. Offshore forcing associated with boundary currents imposes cross-shore and alongshore pressure gradients on the shelf driving coastal currents to flow, in general, the same direction as the boundary currents [Palma et al, 2008;Xu and Oey, 2011;Wood et al, 2016].…”

Section: Introductionmentioning

confidence: 99%

Summertime coastal current reversal opposing offshore forcing and local wind near the middle east coast of Korea: Observation and dynamics

Park

Chang

Nam

2016

Geophysical Research Letters

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A 6 year long current measurement at a buoy station off the middle east coast of Korea reveals an equatorward reversal of coastal current in summer opposing poleward local wind stress and offshore boundary current. The current reversal extends about 40 km offshore from the coast and is concurrent with warming and freshening of water column. Estimates of the depth‐averaged alongshore momentum balance suggest a major balance between the alongshore pressure gradient and the lateral friction. Sources of the pressure gradient for the summertime current reversal are identified as the alongshore buoyancy gradient driven by the wind curl gradient and the prevalence of warmer and lower salinity water in the north. Alongshore pressure gradient and velocity induced by the wind curl gradient are quantified, which yields the observed seasonal current reversal.

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“…They both have the correct mean flow pattern. This mean flow is well known, based on hydrography, drifters, shipboard current profiles, and moored current observations (see Beardsley and Boicourt 1981 for an early summary; also Lentz 2008a, b) as well as numerical modeling over many years (Blumberg and Galperin 1990;Xu and Oey 2011). The mean surface flow is 2 to 12 cm s −1 directed southward on the shelf and offshore.…”

Section: Comparison Between Currents From Nyhops and Hf Radarmentioning

confidence: 76%

Assessing the fidelity of surface currents from a coastal ocean model and HF radar using drifting buoys in the Middle Atlantic Bight

2012

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The rapid expansion of urbanization along the world's coastal areas requires a more comprehensive and accurate understanding of the coastal ocean. Over the past several decades, numerical ocean circulation models have tried to provide such insight, based on our developing understanding of physical ocean processes. The systematic establishment of coastal ocean observation systems adopting cutting-edge technology, such as high frequency (HF) radar, satellite sensing, and gliders, has put such ocean model predictions to the test, by providing comprehensive observational datasets for the validation of numerical model forecasts. The New York Harbor Observing and Prediction System (NYHOPS) is a comprehensive system for understanding coastal ocean processes on the continental shelf waters of New York and New Jersey. To increase confidence in the system's ocean circulation predictions in that area, a detailed validation exercise was carried out using HF radar and Lagrangian drifter-derived surface currents from three drifters obtained between March and October 2010. During that period, the root mean square (RMS) differences of both the eastwest and north-south currents between NYHOPS and HF radar were approximately 15 cm s −1 . Harmonic analysis of NYHOPS and HF radar surface currents shows similar tidal ellipse parameters for the dominant M 2 tide, with a mean difference of 2.4 cm s −1 in the semi-major axis and 1.4 cm s −1 in the semi-minor axis and 3°in orientation and 10°in phase. Surface currents derived independently from drifters along their trajectories showed that NYHOPS and HF radar yielded similarly accurate results. RMS errors when compared to currents derived along the trajectory of the three drifters were approximately 10 cm s −1 . Overall, the analysis suggests that NYHOPS and HF radar had similar skill in estimating the currents over the continental shelf waters of the Middle Atlantic Bight during this time period. An ensemble-based set of particle tracking simulations using one drifter which was tracked for 11 days showed that the ensemble mean separation generally increases with time in a linear fashion. The separation distance is not dominated by high frequency or short spatial scale wavelengths suggesting that both the NYHOPS and HF radar currents are representing tidal and inertial time scales correctly and resolving some of the smaller scale eddies. The growing ensemble mean separation distance is dominated by errors in the mean flow causing the drifters to slowly diverge from their observed positions. The separation distance for both HF radar and NYHOPS stays below 30 km after 5 days, and the two technologies have similar tracking skill at the 95 % level. For comparison, the ensemble mean distance of a drifter from its initial release location (persistence assumption) is estimated to be greater than 70 km in 5 days.

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The Origin of Along-Shelf Pressure Gradient in the Middle Atlantic Bight

Cited by 41 publications

References 75 publications

Mean circulation in the coastal ocean off northeastern North America from a regional-scale ocean model

Mean circulation in the coastal ocean off northeastern North America from a regional-scale ocean model

Summertime coastal current reversal opposing offshore forcing and local wind near the middle east coast of Korea: Observation and dynamics

Assessing the fidelity of surface currents from a coastal ocean model and HF radar using drifting buoys in the Middle Atlantic Bight

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