Editorial Type:
Article
Article Type:
Research Article

Numerical Investigation of the Middle Atlantic Bight Shelfbreak Frontal Circulation Using a High-Resolution Ocean Hindcast Model

Ke Chen Department of Marine, Earth and Atmospheric Sciences, North Carolina State University, Raleigh, North Carolina

Search for other papers by Ke Chen in
Current site
Google Scholar
PubMed Close
and
Ruoying He Department of Marine, Earth and Atmospheric Sciences, North Carolina State University, Raleigh, North Carolina

Search for other papers by Ruoying He in
Current site
Google Scholar
PubMed Close
Print Publication:
01 May 2010
DOI:
https://doi.org/10.1175/2009JPO4262.1
Page(s):
949–964
Restricted access

Abstract

A nested high-resolution ocean model is used to hindcast the Middle Atlantic Bight (MAB) shelfbreak circulation from December 2003 to June 2008. The model is driven by tidal harmonics, realistic atmospheric forcing, and dynamically consistent initial and open boundary conditions obtained from a large-scale circulation model. Simulated shelfbreak sea levels and tracer fields compare favorably with satellite observations and available in situ hydrographic climatology, demonstrating the utility of this nested ocean model for resolving the MAB shelfbreak circulation. The resulting time and space continuous hindcast solutions between January 2004 and December 2007 are used to describe the mean structures and temporal variations of the shelfbreak front and jet, the bottom boundary layer detachment, and the migration of the shelfbreak front. It is found that the shelfbreak jet and boundary convergence reach their maximum intensities in the spring, at which time the foot of the front also migrates to its farthest offshore position. Vorticity analyses reveal that the magnitude ratio of the mean relative vorticity between the seaward and the shoreward portions of the shelfbreak front is about 2:1. The shelfbreak ageostrophic circulation is largely controlled by the viscosity in the boundary layers and by the nonlinear advection in the flow interior. Simulated three-dimensional velocity and tracer fields are used to estimate the transport and heat and salt fluxes across the 200-m isobath. Within the model domain, the total cross-shelf water transport, the total eddy heat flux, and the total eddy salt flux are 0.035 ± 0.26 Sv (1 Sv ≡ 106 m3 s−1), 1.0 × 103 ± 4 × 104 W m−2, and 6.7 × 10−5 ± 7.0 × 10−4 kg m−2 s−1. The empirical orthogonal function (EOF) analysis on the 4-yr shelfbreak circulation hindcast solutions identifies two dominant modes. The first EOF mode accounts for 61% variance, confirming that the shelfbreak jet is a persistent year-round circulation feature. The second mode accounts for 13% variance, representing the baroclinic eddy passages across the shelf break.

Corresponding author address: Dr. Ruoying He, Department of Marine, Earth and Atmospheric Sciences, North Carolina State University, Raleigh, NC 27695. Email: rhe@ncsu.edu

Abstract

A nested high-resolution ocean model is used to hindcast the Middle Atlantic Bight (MAB) shelfbreak circulation from December 2003 to June 2008. The model is driven by tidal harmonics, realistic atmospheric forcing, and dynamically consistent initial and open boundary conditions obtained from a large-scale circulation model. Simulated shelfbreak sea levels and tracer fields compare favorably with satellite observations and available in situ hydrographic climatology, demonstrating the utility of this nested ocean model for resolving the MAB shelfbreak circulation. The resulting time and space continuous hindcast solutions between January 2004 and December 2007 are used to describe the mean structures and temporal variations of the shelfbreak front and jet, the bottom boundary layer detachment, and the migration of the shelfbreak front. It is found that the shelfbreak jet and boundary convergence reach their maximum intensities in the spring, at which time the foot of the front also migrates to its farthest offshore position. Vorticity analyses reveal that the magnitude ratio of the mean relative vorticity between the seaward and the shoreward portions of the shelfbreak front is about 2:1. The shelfbreak ageostrophic circulation is largely controlled by the viscosity in the boundary layers and by the nonlinear advection in the flow interior. Simulated three-dimensional velocity and tracer fields are used to estimate the transport and heat and salt fluxes across the 200-m isobath. Within the model domain, the total cross-shelf water transport, the total eddy heat flux, and the total eddy salt flux are 0.035 ± 0.26 Sv (1 Sv ≡ 106 m3 s−1), 1.0 × 103 ± 4 × 104 W m−2, and 6.7 × 10−5 ± 7.0 × 10−4 kg m−2 s−1. The empirical orthogonal function (EOF) analysis on the 4-yr shelfbreak circulation hindcast solutions identifies two dominant modes. The first EOF mode accounts for 61% variance, confirming that the shelfbreak jet is a persistent year-round circulation feature. The second mode accounts for 13% variance, representing the baroclinic eddy passages across the shelf break.

Corresponding author address: Dr. Ruoying He, Department of Marine, Earth and Atmospheric Sciences, North Carolina State University, Raleigh, NC 27695. Email: rhe@ncsu.edu

Save
Cover Journal of Physical Oceanography
Journal of Physical Oceanography

  • Aikman III, F., H. W. Ou, and R. W. Houghton, 1988: Current variability across the New England continental shelf-break and slope. Cont. Shelf Res., 8 , 625–651.

    • Search Google Scholar
    • Export Citation

  • Barth, J. A., D. Bogucki, S. D. Pierce, and P. M. Kosro, 1998: Se condary circulation associated with a shelfbreak front. Geophys. Res. Lett., 25 , 2761–2764.

    • Search Google Scholar
    • Export Citation

  • Beardsley, R. C., and C. N. Flagg, 1976: The water structure, mean currents, and shelf/slope water front on the New England continental shelf. Mem Soc. Roy. Sci. Liege, 6 , 209–225.

    • Search Google Scholar
    • Export Citation

  • Beardsley, R. C., and W. C. Boicourt, 1981: On estuarine and continental-shelf circulation in the Middle Atlantic Bight. Evolution of Physical Oceanography, B. A. Warren and C. Wunsch, Eds., MIT Press, 198–233.

    • Search Google Scholar
    • Export Citation

  • Beardsley, R. C., D. C. Chapman, K. H. Brink, S. R. Ramp, and R. Schlitz, 1985: The Nantucket Shoals Flux Experiment (NSFE79). Part I: A basic description of the current and temperature variability. J. Phys. Oceanogr., 15 , 713–748.

    • Search Google Scholar
    • Export Citation

  • Burrage, D. M., and R. W. Garvine, 1988: Summertime hydrography at the shelfbreak front in the Middle Atlantic Bight. J. Phys. Oceanogr., 18 , 1309–1319.

    • Search Google Scholar
    • Export Citation

  • Chapman, D. C., 2000: Boundary layer control of buoyant coastal currents and the establishment of a shelfbreak front. J. Phys. Oceanogr., 30 , 2941–2955.

    • Search Google Scholar
    • Export Citation

  • Chapman, D. C., and R. C. Beardsley, 1989: On the origin of shelf water in the Middle Atlantic Bight. J. Phys. Oceanogr., 19 , 384–391.

    • Search Google Scholar
    • Export Citation

  • Chapman, D. C., and S. J. Lentz, 1994: Trapping of a coastal density front by the bottom boundary layer. J. Phys. Oceanogr., 24 , 1464–1479.

    • Search Google Scholar
    • Export Citation

  • Chassignet, E. P., H. E. Hurlburt, O. M. Smedstad, G. R. Halliwell, P. J. Hogan, A. J. Wallcraft, R. Baraille, and R. Bleck, 2006: The HYCOM (Hybrid Coordinate Ocean Model) data assimilative system. J. Mar. Syst., 65 , 60–83.

    • Search Google Scholar
    • Export Citation

  • Fairall, C. W., E. F. Bradley, J. E. Hare, A. A. Garchev, and J. Edson, 2003: Bulk parameterization of air–sea fluxes: Updates and verification for the COARE algorithm. J. Climate, 16 , 571–591.

    • Search Google Scholar
    • Export Citation

  • Flagg, C. N., R. W. Houghton, and L. J. Pietrafesa, 1994: Summertime thermocline salinity maximum intrusions in the Middle Atlantic Bight. Deep-Sea Res. II, 41 , 325–340.

    • Search Google Scholar
    • Export Citation

  • Flagg, C. N., M. Dunn, D-P. Wang, H. T. Rossby, and R. L. Benway, 2006: A study of the currents of the outer shelf and upper slope from a decade of shipboard ADCP observations in the Middle Atlantic Bight. J. Geophys. Res., 111 , C06003. doi:10.1029/2005JC003116.

    • Search Google Scholar
    • Export Citation

  • Flather, R. A., 1976: A tidal model of the northwest European continental shelf. Mem. Soc. Roy. Sci. Liege, 6 , 141–164.

  • Fratantoni, P. S., and R. S. Pickart, 2003: Variability of the shelf break jet in the Middle Atlantic Bight: Internally or externally forced? J. Geophys. Res., 10 , 3166. doi:10.1029/2002JC001326.

    • Search Google Scholar
    • Export Citation

  • Fratantoni, P. S., R. S. Pickart, D. J. Torres, and A. Scotti, 2001: Mean structure and dynamics of the shelfbreak jet in the Middle Atlantic Bight during fall and winter. J. Phys. Oceanogr., 31 , 2135–2156.

    • Search Google Scholar
    • Export Citation

  • Garvine, R. W., K-C. Wong, G. G. Gawarkiewicz, R. K. McCarthy, R. W. Houghton, and F. Aikman III, 1988: The morphology of shelf break eddies. J. Geophys. Res., 93 , 15593–15607.

    • Search Google Scholar
    • Export Citation

  • Garvine, R. W., K-C. Wong, and G. G. Gawarkiewicz, 1989: Quantitative properties of shelfbreak eddies. J. Geophys. Res., 94 , 14475–14483.

    • Search Google Scholar
    • Export Citation

  • Gawarkiewicz, G. G., and D. C. Chapman, 1992: The role of stratification in the formation and maintenance of shelf-break fronts. J. Phys. Oceanogr., 22 , 753–772.

    • Search Google Scholar
    • Export Citation

  • Gawarkiewicz, G. G., F. Bahr, R. C. Bearsley, and K. H. Brink, 2001: Interaction of a Slope Eddy with the Shelfbreak Front in the Middle Atlantic Bight. J. Phys. Oceanogr., 31 , 2783–2796.

    • Search Google Scholar
    • Export Citation

  • Gawarkiewicz, G. G., K. H. Brink, R. C. Bearsley, M. Caruso, J. F. Lynch, and C. Chiu, 2004: A large-amplitude meander of the shelfbreak front during summer south of New England: Observations from the Shelfbreak PRIMER experiment. J. Geophys. Res., 109 , C03006. doi:10.1029/2002JC001468.

    • Search Google Scholar
    • Export Citation

  • He, R., and R. H. Weisberg, 2002: West Florida shelf circulation and temperature budget for the 1999 spring transition. Cont. Shelf Res., 22 , 719–748.

    • Search Google Scholar
    • Export Citation

  • He, R., and J. L. Wilkin, 2006: Barotropic tides on the southeast New England shelf: A view from a hybrid data assimilative modeling approach. J. Geophys. Res., 111 , C08002. doi:10.1029/2005JC003254.

    • Search Google Scholar
    • Export Citation

  • He, R., D. J. McGillicuddy, D. R. Lynch, K. W. Smith, C. A. Stock, and J. P. Manning, 2005: Data assimilative hindcast of the Gulf of Maine coastal circulation. J. Geophys. Res., 110 , C10011. doi:10.1029/2004JC002807.

    • Search Google Scholar
    • Export Citation

  • Houghton, R. W., R. Schlitz, R. C. Beardsley, B. Butman, and J. L. Chamberlin, 1982: The Middle Atlantic Bight cold pool: Evolution of the temperature structure in summer 1979. J. Phys. Oceanogr., 12 , 1019–1029.

    • Search Google Scholar
    • Export Citation

  • Houghton, R. W., F. Aikman III, and H. W. Ou, 1988: Shelf-slope water frontal structure, and cross-shelf exchange at the New England shelfbreak. Cont. Shelf Res., 8 , 687–710.

    • Search Google Scholar
    • Export Citation

  • Houghton, R. W., C. N. Flagg, and L. J. Pietrafesa, 1994: Shelf-slope water frontal structure, motion, and eddy heat flux in the southern Middle Atlantic Bight. Deep-Sea Res. II, 41 , 273–306.

    • Search Google Scholar
    • Export Citation

  • Lentz, S. J., 2008: Observations and a model of the mean circulation over the Middle Atlantic Bight continental shelf. J. Phys. Oceanogr., 38 , 1203–1221.

    • Search Google Scholar
    • Export Citation

  • Linder, C. A., and G. Gawarkiewicz, 1998: A climatology of the shelf break front in the Middle Atlantic Bight. J. Geophys. Res., 103 , 18405–18423.

    • Search Google Scholar
    • Export Citation

  • Linder, C. A., G. Gawarkiewicz, and R. S. Pickart, 2004: Seasonal characteristics of bottom boundary layer detachment at the shelfbreak front in the Middle Atlantic Bight. J. Geophys. Res., 109 , C03049. doi:10.1029/2003JC002032.

    • Search Google Scholar
    • Export Citation

  • Loder, J. W., B. Petrie, and G. Gawarkiewicz, 1998: The coastal ocean off northeastern North America: A large-scale view. The Sea: The Global Coastal Ocean, Vol. 11, Regional Studies and Syntheses, A. R. Robinson and K. H. Brink, Eds., Wiley, 105–133.

    • Search Google Scholar
    • Export Citation

  • Lozier, M. S., and G. Gawarkiewicz, 2001: Cross-frontal exchange in the Middle Atlantic Bight as evidenced by surface drifters. J. Phys. Oceanogr., 31 , 2498–2510.

    • Search Google Scholar
    • Export Citation

  • Lozier, M. S., M. S. C. Reed, and G. G. Gawarkiewicz, 2002: Instability of a shelfbreak front. J. Phys. Oceanogr., 32 , 924–944.

  • Luettich Jr., R. A., J. J. Westerink, and N. W. Scheffner, 1992: ADCIRC: An advanced three- dimensional circulation model for shelves, coasts and estuaries, report 1: Theory and methodology of ADCIRC-2DDI and ADCIRC-3DL. U.S. Army Corps of Engineers Tech. Rep. DRP-92-6, 137 pp.

    • Search Google Scholar
    • Export Citation

  • Marchesiello, P., J. C. McWilliams, and A. Shchepetkin, 2001: Open boundary conditions for long-term integration of regional oceanic models. Ocean Modell., 3 , 1–20.

    • Search Google Scholar
    • Export Citation

  • Marra, J., R. W. Houghton, D. C. Boardman, and P. J. Neale, 1982: Variability in surface chlorophyll a at a shelf-break front. J. Mar. Res., 40 , 575–591.

    • Search Google Scholar
    • Export Citation

  • Marra, J., R. W. Houghton, and C. Garside, 1990: Phytoplankton growth at the shelf-break front in the Middle Atlantic Bight. J. Mar. Res., 48 , 851–868.

    • Search Google Scholar
    • Export Citation

  • Mellor, G. L., and T. Yamada, 1982: Development of a turbulence closure model for geophysical fluid problems. Rev. Geophys., 20 , 851–875.

    • Search Google Scholar
    • Export Citation

  • Pickart, R. S., 2000: Bottom boundary layer structure and detachment in the shelfbreak jet of the Middle Atlantic Bight. J. Phys. Oceanogr., 30 , 2668–2686.

    • Search Google Scholar
    • Export Citation

  • Rio, M-H., and F. Hernadez, 2004: A mean dynamic topography computed over the world ocean from altimetry, in situ measurements, and a geoid model. J. Geophys. Res., 109 , C12032. doi:10.1029/2003JC002226.

    • Search Google Scholar
    • Export Citation

  • Ryan, J. P., J. A. Yoder, J. A. Bath, and P. C. Cornillon, 1999a: Chlorophyll enhancement and mixing associated with meanders of the shelf break front in the Mid-Atlantic Bight. J. Geophys. Res., 104 , (C10). 23479–23493.

    • Search Google Scholar
    • Export Citation

  • Ryan, J. P., J. A. Yoder, and P. C. Cornillon, 1999b: Enhanced chlorophyll at the shelfbreak of the Mid-Atlantic Bight and Georges Bank during the spring transition. Limnol. Oceanogr., 44 , 1–11.

    • Search Google Scholar
    • Export Citation

  • Shchepetkin, A. F., and J. C. McWilliams, 2005: The Regional Oceanic Modeling System (ROMS): A split-explicit, free surface, topography-following-coordinate oceanic model. Ocean Modell., 9 , 347–404.

    • Search Google Scholar
    • Export Citation
All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 441 182 52
PDF Downloads 309 120 6