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  • Mellor, George L.  (10)
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  • 1
    Online Resource
    Online Resource
    Diagnostic and prognostic calculations of the North Atlantic circulation and sea level using a sigma coordinate ocean model
    American Geophysical Union (AGU) ; 1994
    In:  Journal of Geophysical Research: Oceans Vol. 99, No. C7 ( 1994-07-15), p. 14159-14171
    Details
    In: Journal of Geophysical Research: Oceans, American Geophysical Union (AGU), Vol. 99, No. C7 ( 1994-07-15), p. 14159-14171
    Abstract: The North Atlantic circulation and sea surface height, determined from hydrographic and wind stress data are calculated with a free surface, primitive equation ocean model. The model grid, a vertical sigma ‐ coordinate and horizontal curvilinear orthogonal system, makes it possible to resolve coastal regions with complicated topography that were unresolved in previous calculations. When running in a diagnostic mode, in which the temperature and the salinity fields are fixed and equal to the Levitus annual mean fields, the vertically integrated North Atlantic circulation is very similar to though more detailed than that obtained from previous calculations using simpler diagnostic models. On the other hand, the meridional, zonally averaged flows and the poleward heat transport from the purely diagnostic calculations are noisy and unrealistic. However, short prognostic calculations of only 30 days following the diagnostic run allow intensification of the western boundary current and removal of noise due to inconsistencies between the hydrographic data and bottom topography and produce a more realistic meridional circulation and poleward heat transport, with a maximum value of 1.2×10 15 W which is, comparable to estimates based on observations. The calculated sea level along the North America continent agrees with previous estimates but provides more spatial detail. Analysis of the dynamic adjustment process shows that this process is dominated by the effect of bottom topography through the action of the bottom pressure torque. This study is a first step in applying a realistic numerical model, previously used primarily for estuaries and coastal regions, to basin‐scale ocean problems.
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/94JC00859
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1994
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  • 2
    Online Resource
    Online Resource
    On the interpentadal variability of the North Atlantic Ocean: Model simulated changes in transport, meridional heat flux and coastal sea level between 1955–1959 and 1970–1974
    American Geophysical Union (AGU) ; 1995
    In:  Journal of Geophysical Research: Oceans Vol. 100, No. C6 ( 1995-06-15), p. 10559-10566
    Details
    In: Journal of Geophysical Research: Oceans, American Geophysical Union (AGU), Vol. 100, No. C6 ( 1995-06-15), p. 10559-10566
    Abstract: Previous studies by Greatbatch et al. (1991) indicate significant changes in the North Atlantic thermohaline structure and circulation between the pentads 1955–1959 and 1970–1974, using data analyzed by Levitus (1989a,b,c) and a simple diagnostic model by Mellor et al. (1982). In this paper these changes are modeled using a three‐dimensional, free surface, coastal ocean model. Diagnostic and short‐term prognostic calculations are used to infer the dynamically adjusted fields corresponding to the observed hydrographic and wind stress climatology of each pentad. While the results agree with earlier studies indicating that the Gulf Stream was considerably weaker (by about 30 Sv) during the 1970s compared to the 1950s, they also indicate some changes in the poleward heat transport, although the statistical significance of these changes relative to sampling errors in the data is not clear. The change of wind pattern between the two pentads, associated with changes in sea surface temperature, resulted in changes in the Ekman contribution to the poleward heat flux transport. The modeled sea level along the North American coast shows a sea level rise of about 5–10 cm between 1955–1959 and 1970–1974; a comparison with observed sea level at 15 tide gage stations shows good agreement. Most of the coastal sea level change is attributed to changes in thermohaline ocean circulation and wind stress; thermal expansion seems to play a lesser role. The methodology tested here demonstrates an effective way to estimate climate changes in ocean circulation and sea level from observed hydrographic data and winds using ocean models to enhance and analyze the data.
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/95JC00659
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1995
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  • 3
    Online Resource
    Online Resource
    Sea level variations induced by heating and cooling: An evaluation of the Boussinesq approximation in ocean models
    American Geophysical Union (AGU) ; 1995
    In:  Journal of Geophysical Research: Oceans Vol. 100, No. C10 ( 1995-10-15), p. 20565-20577
    Details
    In: Journal of Geophysical Research: Oceans, American Geophysical Union (AGU), Vol. 100, No. C10 ( 1995-10-15), p. 20565-20577
    Abstract: In this paper a sigma coordinate ocean model is modified to remove the commonly used Boussinesq approximation so that the effect of thermal expansion is exactly included in the basic equations in order to cope with the seasonal heating cycle and the detection of climate change through variation in sea level height. Tests are performed to evaluate the differences between Boussinesq and non‐Boussinesq calculations under different heating and cooling conditions and different model domains. For an idealized case of a flat bottom, shallow ocean basin without wind forcing, simulations of a warm eddy show that the non‐Boussinesq dynamics have only a minor effect on the baroclinic current field. However, vertically averaged velocities, though small compared with the baroclinic velocities, are cyclonic for the Boussinesq calculation and anticyclonic for the non‐Boussinesq calculation. The results indicate that global or closed basin Boussinesq models should be able to simulate most of the observed steric sea level changes on seasonal or climate timescales, when corrected by a spatially uniform, time‐dependent factor calculated from the volume‐averaged density change. The seasonal variation of the globally averaged sea level calculated from climatological data is small, about 1 cm. Variations in steric sea level in regional models, both Boussinesq and non‐Boussinesq, may differ from those of global models owing to the unknown transport across their boundaries associated with the local heating and cooling. A spatially uniform, time‐dependent correction, similar to that associated with thermal expansion, is proposed to account for transport across open boundaries of regional models. Variations of sea level obtained from a Boussinesq model of the Atlantic Ocean approximate the seasonal signal due to the heating/cooling cycle of each hemisphere as observed by satellite altimeter data.
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/95JC02442
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1995
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    SSG: 16,13
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  • 4
    Online Resource
    Online Resource
    A Numerical Study of the Variability and the Separation of the Gulf Stream, Induced by Surface Atmospheric Forcing and Lateral Boundary Flows
    American Meteorological Society ; 1992
    In:  Journal of Physical Oceanography Vol. 22, No. 6 ( 1992-06), p. 660-682
    Details
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 22, No. 6 ( 1992-06), p. 660-682
    Type of Medium: Online Resource
    ISSN: 0022-3670 , 1520-0485
    URL: Article
    DOI: 10.1175/1520-0485(1992)022〈0660:ANSOTV〉2.0.CO;2
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 1992
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  • 5
    Online Resource
    Online Resource
    Data Assimilation Experiments in the Gulf Stream Region: How Useful Are Satellite-Derived Surface Data for Nowcasting the Subsurface Fields?
    American Meteorological Society ; 1997
    In:  Journal of Atmospheric and Oceanic Technology Vol. 14, No. 6 ( 1997-12), p. 1379-1391
    Details
    In: Journal of Atmospheric and Oceanic Technology, American Meteorological Society, Vol. 14, No. 6 ( 1997-12), p. 1379-1391
    Type of Medium: Online Resource
    ISSN: 0739-0572 , 1520-0426
    URL: Article
    DOI: 10.1175/1520-0426(1997)014〈1379:DAEITG〉2.0.CO;2
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 1997
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  • 6
    Online Resource
    Online Resource
    A Comparison of Gulf Stream Sea Surface Height Fields Derived from Geosat Altimeter Data and Those Derived from Sea Surface Temperature Data
    American Meteorological Society ; 1993
    In:  Journal of Atmospheric and Oceanic Technology Vol. 10, No. 1 ( 1993), p. 76-
    Details
    In: Journal of Atmospheric and Oceanic Technology, American Meteorological Society, Vol. 10, No. 1 ( 1993), p. 76-
    Type of Medium: Online Resource
    ISSN: 0739-0572 , 1520-0426
    URL: Article
    DOI: 10.1175/1520-0426(1993)010〈0076:ACOGSS〉2.0.CO;2
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 1993
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  • 7
    Online Resource
    Online Resource
    Simulations of the Atlantic Ocean with a free surface sigma coordinate ocean model
    American Geophysical Union (AGU) ; 1997
    In:  Journal of Geophysical Research: Oceans Vol. 102, No. C7 ( 1997-07-15), p. 15647-15657
    Details
    In: Journal of Geophysical Research: Oceans, American Geophysical Union (AGU), Vol. 102, No. C7 ( 1997-07-15), p. 15647-15657
    Abstract: A sigma coordinate, free surface numerical model with turbulence dynamics has been implemented for the Atlantic Ocean and the Greenland Sea, from 80°S to 80°N. It is driven at the surface by monthly mean sea surface temperature and wind stress climatologies and is executed for 30 years. This is the first time that a model of this type, previously used mostly for coastal and regional simulations, has been implemented for the entire Atlantic Ocean and run for a long period of time. The model horizontal circulation, thermohaline overturning circulation, and meridional heat fluxes are described; the results are compared with observations and the results of other models. The model produces intense deep western boundary currents and complicated gyre structures associated with small‐scale topographic variations. The meridional overturning circulation consists of about 14 Sv (1 Sv=10 6 m 3 s −1 ) of southward flowing deep water mass crossing the equator and a northward heat flux with a maximum value of more than 1 PW (10 15 W). Although the maximum meridional heat flux is comparable to estimates obtained from observations, the amplitude of the seasonal variations of northward heat flux across 26°N is underestimated in comparison with observations; it is similar to that obtained by other models.
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/97JC00984
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1997
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    SSG: 16,13
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  • 8
    Online Resource
    Online Resource
    A Gulf Stream model and an altimetry assimilation scheme
    American Geophysical Union (AGU) ; 1991
    In:  Journal of Geophysical Research: Oceans Vol. 96, No. C5 ( 1991-05-15), p. 8779-8795
    Details
    In: Journal of Geophysical Research: Oceans, American Geophysical Union (AGU), Vol. 96, No. C5 ( 1991-05-15), p. 8779-8795
    Abstract: A continuous data assimilation scheme and a multilayer, primitive equation, numerical model are described. The model is an eddy‐resolving, coastal ocean model that has been extended to include the Gulf Stream region. It has complete thermohaline dynamics, a bottom‐following, sigma, vertical coordinate system, and a coastal‐following, curvilinear orthogonal, horizontal coordinate system. Calculated model fields are used to provide a model climatology and correlations between subsurface temperature and salinity anomalies and surface elevation anomalies. An optimal interpolation method, the surface to subsurface correlations, and estimated model and data errors are the basis of the assimilation technique. Altimetry anomaly data extracted from the model calculations according to the Geosat orbital schedule are used to test the assimilation scheme and to provide nowcasts and forecasts. Sensitivity studies are performed to test the effects of various parameters of the scheme. It is found that the scheme is less efficient in the shallow continental shelf area than in the deeper regions of the model. The results show significant nowcast skill, with area‐averaged rms error for surface elevation and subsurface properties of about 40–50% of the corresponding error of the unassimilated case. Good forecast skill, better than persistence, is demonstrated for 10–20 days; there is little skill after 30–40 days. Increasing the density of the satellite altimetry data (especially by decreasing the separation distance between tracks) should decrease the nowcast rms error to about 15% and improve the forecast.
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/91JC00383
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1991
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    SSG: 16,13
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  • 9
    Online Resource
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    A generalized coordinate ocean model and a comparison of the bottom boundary layer dynamics in terrain-following and in z-level grids
    Elsevier BV ; 2004
    In:  Ocean Modelling Vol. 6, No. 3-4 ( 2004-1), p. 379-403
    Details
    In: Ocean Modelling, Elsevier BV, Vol. 6, No. 3-4 ( 2004-1), p. 379-403
    Type of Medium: Online Resource
    ISSN: 1463-5003
    URL: Article
    DOI: 10.1016/S1463-5003(03)00026-X
    Language: English
    Publisher: Elsevier BV
    Publication Date: 2004
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    SSG: 14
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  • 10
    Online Resource
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    Continuous Assimilation of Geosat Altimeter Data into a Three-Dimensional Primitive Equation Gulf Stream Model
    American Meteorological Society ; 1994
    In:  Journal of Physical Oceanography Vol. 24, No. 4 ( 1994-04), p. 832-847
    Details
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 24, No. 4 ( 1994-04), p. 832-847
    Type of Medium: Online Resource
    ISSN: 0022-3670 , 1520-0485
    URL: Article
    DOI: 10.1175/1520-0485(1994)024〈0832:CAOGAD〉2.0.CO;2
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 1994
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