Dynamics of mean and subtidal flow on the New England shelf

American Geophysical Union (AGU) - Tập 108 Số C8 - 2003
R. Kipp Shearman1, Steven J. Lentz1
1Department of Physical Oceanography, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA.

Tóm tắt

Current and hydrographic observations from the Coastal Mixing and Optics experiment moored array, deployed from August 1996 through June 1997, are used to describe the velocity variability and evaluate the dynamics of circulation over the New England shelf on timescales ranging from a few days to several months. Subtidal (days to weeks) current variability was polarized along‐isobath and dominated by episodic bursts of westward flow. The along‐isobath subtidal flow was primarily geostrophic and barotropic, and was correlated with large‐scale along‐coast wind stress fluctuations oriented 45°T (65° counterclockwise from the local isobath orientation). Subtidal near‐surface ageostrophic transport matched estimates of wind‐driven Ekman transport; however, near‐bottom ageostrophic transport was much larger than estimates of Ekman transport from bottom stress. Low‐frequency (monthly and longer timescales) flow was generally westward and off‐shelf at all sites and depths, with the strongest westward flow during the fall. Low‐frequency along‐isobath currents were primarily geostrophic with baroclinic and barotropic components of similar magnitude. Depth‐averaged ageostrophic transport was quantitatively consistent with Ekman transport from wind and bottom stress. Measured bottom stress at both subtidal and low‐frequency timescales was weak, nearly an order of magnitude smaller than the wind stress. Low‐frequency fluctuations in the predominantly geostrophic along‐isobath flow were attributable to variations in the cross‐shelf density field associated with the seasonal cycle in surface heating. During the fall, thermal wind shear was strongest, because the cross‐isobath temperature gradient was acting in concert with the persistent cross‐isobath salinity gradient to enhance the cross‐isobath density gradient (i.e., warmer and fresher water inshore). During the winter, in response to surface cooling, the cross‐isobath temperature gradient reversed sign, reducing the cross‐isobath density gradient (i.e., cooler and fresher water inshore).

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Tài liệu tham khảo

10.1016/0278-4343(88)90069-6

10.1146/annurev.fl.12.010180.002133

10.1029/JC092iC02p01845

10.1175/1520-0485(1981)011<0355:MSOTWD>2.0.CO;2

10.1175/1520-0485(1979)009<0612:OTMCIT>2.0.CO;2

10.1175/1520-0485(1985)015<0713:TNSFEP>2.0.CO;2

Bigelow H. B., 1933, Studies of the waters on the continental shelf, Cape Cod to Chesapeake Bay: I. The cycle of temperature, Pap. Phys. Oceanogr. Meteorol., 2, 1

10.1175/1520-0485(1985)015<0749:TNSFEP>2.0.CO;2

10.1029/JC092iC02p01605

10.1029/2000JC900069

10.1175/1520-0485(1994)024<1464:TOACDF>2.0.CO;2

10.1175/1520-0485(1986)016<0758:OTCOMF>2.0.CO;2

10.1029/JC081i030p05389

10.1175/1520-0485(1978)008<0047:TATW>2.0.CO;2

10.1029/2000JC900155

10.1175/1520-0426(1998)015<0547:DCFEFM>2.0.CO;2

10.1029/95JC03205

Galbraith N. A.Plueddemann S.Lentz S.Anderson M.Baumgartner andJ.Edson Coastal Mixing and Optics experiment moored array data report Tech. Rept. WHOI‐99‐15 Woods Hole Oceanogr. Inst. Woods Hole Mass. 1999.

10.1146/annurev.fl.25.010193.001451

10.1029/97JC00442

10.1175/1520-0426(1994)011<1625:SSPDFB>2.0.CO;2

10.1175/1520-0485(1982)012<1019:TMABCP>2.0.CO;2

10.1016/0278-4343(88)90072-6

Islen C. O., 1936, A study of the circulation of the western North Atlantic, Pap. Phys. Oceanogr. Meteorol., 2, 1

10.1175/1520-0485(1985)015<0544:NIWPIG>2.0.CO;2

10.1029/2001JC001121

Limeburner R., 1982, The seasonal hydrography and circulation over Nantucket Shoals, J. Mar. Res., 40, 371

10.1029/98JC01438

Martin M. J. An investigation of momentum exchange parameterizations and atmospheric forcing for the Coastal Mixing and Optics program Master's thesis Mass. Inst. of Technol./Woods Hole Oceanogr. Inst. Woods Hole Mass. 1998.

10.1175/1520-0485(1983)013<2125:OTLSAD>2.0.CO;2

10.1175/1520-0485(1981)011<1383:AAOSCF>2.0.CO;2

10.1175/1520-0485(1974)004<0003:OCJAUI>2.0.CO;2

10.1175/1520-0485(1992)022<0523:SROSSC>2.0.CO;2

10.1175/1520-0485(1992)022<0542:SROSSC>2.0.CO;2

10.1029/2000JC000240

10.1073/pnas.69.11.3380

Wang D. P., 1979, Low‐frequency sea level variability on the Middle Atlantic Bight, J. Mar. Res., 37, 683

10.1175/1520-0426(1987)004<0312:MOTITO>2.0.CO;2

10.1146/annurev.fl.12.010180.001415

10.1175/1520-0485(1986)016<0947:TSSBRO>2.0.CO;2