The Experts below are selected from a list of 120 Experts worldwide ranked by ideXlab platform

Kirk Bryan - One of the best experts on this subject based on the ideXlab platform.

  • comparison of thermally driven circulations from a depth coordinate model and an Isopycnal Layer model part ii the difference and structure of the circulations
    Journal of Physical Oceanography, 2001
    Co-Authors: Younggyu Park, Kirk Bryan
    Abstract:

    Thermally driven ocean circulations in idealized basins are calculated with two well-known model codes, one based on depth-level coordinates and the other based on Isopycnal coordinates. In addition, the two models have very different representations of convection. In the level-coordinate model, convective adjustment is used, while in the Isopycnal-coordinate model, convection is simulated by a transformation of the surface Layer to the Layer below. Both models indicate a three-Layer structure in the circulation. The lower and middle Layers have a flow structure that corresponds with the classical abyssal circulation models. The upper flow is strongly constrained by the buoyancy flux field at the upper surface and the convective parameterization. The model with convective adjustment and level coordinates is dominated by an eastward flow, which sinks to subsurface level at the eastern boundary. It lacks any indication of a surface cyclonic flow, even in the vicinity of sinking at the northern wall. On the other hand, in the model based on density coordinates the eastward surface flow turns to the north at the eastern boundary and forms a pronounced cyclonic circulation at high latitudes. Due to the cyclonic circulation, the coldest surface water is found near the northwestern corner, while in the level model the coldest water is near the northeastern corner. The Isopycnal model appears to be a more realistic representation of the real ocean since both wind and the thermohaline circulation are thought to contribute to the North Atlantic subarctic cyclonic gyre. Although the zonally averaged buoyancy flux produced by the two model codes is the same, the actual patterns of buoyancy flux at the surface are not similar at high latitudes. This suggests that the two types of numerical models would indicate very different air‐sea interaction if coupled to atmospheric models and used to simulate climate. The application of the Gent‐McWilliams parameterization of mesoscale eddies to the model with z coordinates and convective adjustment reduces the differences between the surface circulation of the two models by a small amount.

  • comparison of thermally driven circulations from a depth coordinate model and an Isopycnal Layer model part i scaling law sensitivity to vertical diffusivity
    Journal of Physical Oceanography, 2000
    Co-Authors: Younggyu Park, Kirk Bryan
    Abstract:

    Abstract Two different types of numerical ocean circulation models are used in a classical idealized problem, the thermally induced circulation in an ocean basin bounded by two meridians to the east and west and by the equator and a line of constant latitude. A simple scaling theory exists for predicting poleward heat transport and the strength of meridional overturning as a function of vertical diffusivity and other external factors. However, previous studies have indicated conflicting results, and other scaling laws have been proposed. Experiments with two widely used types of numerical models, one based on depth coordinates and the other based on Isopycnal Layers, provide insight into the discrepancies of previous studies. In the numerical experiments vertical diffusivity is varied over a range of 200. The source of the difficulty in previous studies is in part traced to applying a fixed restoring coefficient at the upper boundary and considering the buoyancy forcing at the surface fixed irrespective o...

Younggyu Park - One of the best experts on this subject based on the ideXlab platform.

  • comparison of thermally driven circulations from a depth coordinate model and an Isopycnal Layer model part ii the difference and structure of the circulations
    Journal of Physical Oceanography, 2001
    Co-Authors: Younggyu Park, Kirk Bryan
    Abstract:

    Thermally driven ocean circulations in idealized basins are calculated with two well-known model codes, one based on depth-level coordinates and the other based on Isopycnal coordinates. In addition, the two models have very different representations of convection. In the level-coordinate model, convective adjustment is used, while in the Isopycnal-coordinate model, convection is simulated by a transformation of the surface Layer to the Layer below. Both models indicate a three-Layer structure in the circulation. The lower and middle Layers have a flow structure that corresponds with the classical abyssal circulation models. The upper flow is strongly constrained by the buoyancy flux field at the upper surface and the convective parameterization. The model with convective adjustment and level coordinates is dominated by an eastward flow, which sinks to subsurface level at the eastern boundary. It lacks any indication of a surface cyclonic flow, even in the vicinity of sinking at the northern wall. On the other hand, in the model based on density coordinates the eastward surface flow turns to the north at the eastern boundary and forms a pronounced cyclonic circulation at high latitudes. Due to the cyclonic circulation, the coldest surface water is found near the northwestern corner, while in the level model the coldest water is near the northeastern corner. The Isopycnal model appears to be a more realistic representation of the real ocean since both wind and the thermohaline circulation are thought to contribute to the North Atlantic subarctic cyclonic gyre. Although the zonally averaged buoyancy flux produced by the two model codes is the same, the actual patterns of buoyancy flux at the surface are not similar at high latitudes. This suggests that the two types of numerical models would indicate very different air‐sea interaction if coupled to atmospheric models and used to simulate climate. The application of the Gent‐McWilliams parameterization of mesoscale eddies to the model with z coordinates and convective adjustment reduces the differences between the surface circulation of the two models by a small amount.

  • comparison of thermally driven circulations from a depth coordinate model and an Isopycnal Layer model part i scaling law sensitivity to vertical diffusivity
    Journal of Physical Oceanography, 2000
    Co-Authors: Younggyu Park, Kirk Bryan
    Abstract:

    Abstract Two different types of numerical ocean circulation models are used in a classical idealized problem, the thermally induced circulation in an ocean basin bounded by two meridians to the east and west and by the equator and a line of constant latitude. A simple scaling theory exists for predicting poleward heat transport and the strength of meridional overturning as a function of vertical diffusivity and other external factors. However, previous studies have indicated conflicting results, and other scaling laws have been proposed. Experiments with two widely used types of numerical models, one based on depth coordinates and the other based on Isopycnal Layers, provide insight into the discrepancies of previous studies. In the numerical experiments vertical diffusivity is varied over a range of 200. The source of the difficulty in previous studies is in part traced to applying a fixed restoring coefficient at the upper boundary and considering the buoyancy forcing at the surface fixed irrespective o...

Nicolas Kolodziejczyk - One of the best experts on this subject based on the ideXlab platform.

  • Seasonal variability of the equatorial undercurrent termination and associated salinity maximum in the Gulf of Guinea
    Climate Dynamics, 2014
    Co-Authors: Nicolas Kolodziejczyk, Frédéric Marin, Bernard Bourlès, Yves Gouriou, Henrick Berger
    Abstract:

    The termination of the Equatorial Undercurrent (EUC) in the eastern equatorial Atlantic during boreal summer and fall, and the fate of the associated saline water masses, are analyzed from in situ hydrological and currents data collected during 19 hydrographic cruises between 2000 and 2007, complemented by observations from Argo profiling floats and PIRATA moorings, and from a numerical simulation of the Tropical Atlantic Ocean for the period 1993–2007. An intense variability of the circulation and hydrological properties is evidenced from observations in the upper thermocline (24.5–26.2 Isopycnal Layer) between June and November. During early boreal summer, saline water masses are transported eastward in the upper thermocline to the African coast within the EUC, and recirculate westward on both sides of the EUC. In mid-boreal summer, the EUC weakens in the upper thermocline and the equatorial salinity maximum disappears due to intense mixing with the surface waters during the upwelling season. The extra-equatorial salinity maxima are also partially eroded during the boreal summer, with a slight poleward migration of the southern hemisphere maximum until late boreal summer. The upper EUC reappears in September, feeding again the eastern equatorial Atlantic with saline waters until boreal spring. During December–January, numerical results suggest a second seasonal weakening of the EUC in the Gulf of Guinea, with a partial erosion of the associated equatorial salinity maximum.

  • Seasonal variability of the Equatorial Undercurrent at 10°W as inferred from recent in situ observations
    Journal of Geophysical Research, 2009
    Co-Authors: Nicolas Kolodziejczyk, Frédéric Marin, Bernard Bourlès, Jacques Grelet, Remy Chuchla
    Abstract:

    [1] Eighteen cross-equatorial shipboard current profiling sections along 10°W with conductivity-temperature-depth measurements taken between 1997 and 2007 are used to analyze the mean meridional structure and the seasonal variability of the Equatorial Undercurrent (EUC) at 10°W. Our analysis suggests a seasonal cycle for the EUC transport at 10°W, with a well-defined annual harmonic and some indication of a semiannual component, with a first maximum in January and a second stronger maximum from June to September. The mean EUC transport at 10°W is estimated to be 12.1 Sv and, compared to earlier estimates farther in the west, at 35°W (20.9 Sv) and 26°W (13.8 Sv). The eastward flow transport exhibits a strong variability at 10°W (with a total range of transports from 7.1 Sv to more than 31.7 Sv). The seasonal amplitude of the eastward flow variability is ±8.9 Sv, from a minimum of 8.2 Sv in November to 25.9 Sv in August. The eastward flows within the thermocline are divided in two parts: a permanent part within the σθ = 24.5–26.5 Isopycnal Layer, with a semiannual cycle, known as the EUC, and a nonpermanent part in the deep thermocline (beneath σθ = 26.5 Isopycnal), associated with a strong eastward transport (up to 15 Sv) during the boreal summer, that is not observed during the rest of the year. The current at the equator in the deep thermocline is even westward during boreal fall. The disappearance of the salinity core of the EUC during the boreal summer, associated with the upwelling of the hydrological structure at 10°W, reveals that the saline subtropical waters carried by the EUC within the thermocline no longer flow into the Gulf of Guinea during the boreal summer. Our data also show the presence of the South Equatorial Undercurrent (SEUC) at 10°W in the Gulf of Guinea with a strong latitudinal and depth variability throughout the year. The mean SEUC at 10°W is centered near 5°S and is farther south than observed at 35°W and 26°W, suggesting its poleward shift from west to east.

  • seasonal variability of the equatorial undercurrent at 10 w as inferred from recent in situ observations
    Journal of Geophysical Research, 2009
    Co-Authors: Nicolas Kolodziejczyk, Frédéric Marin, Bernard Bourlès, Jacques Grelet, Remy Chuchla
    Abstract:

    [1] Eighteen cross-equatorial shipboard current profiling sections along 10°W with conductivity-temperature-depth measurements taken between 1997 and 2007 are used to analyze the mean meridional structure and the seasonal variability of the Equatorial Undercurrent (EUC) at 10°W. Our analysis suggests a seasonal cycle for the EUC transport at 10°W, with a well-defined annual harmonic and some indication of a semiannual component, with a first maximum in January and a second stronger maximum from June to September. The mean EUC transport at 10°W is estimated to be 12.1 Sv and, compared to earlier estimates farther in the west, at 35°W (20.9 Sv) and 26°W (13.8 Sv). The eastward flow transport exhibits a strong variability at 10°W (with a total range of transports from 7.1 Sv to more than 31.7 Sv). The seasonal amplitude of the eastward flow variability is ±8.9 Sv, from a minimum of 8.2 Sv in November to 25.9 Sv in August. The eastward flows within the thermocline are divided in two parts: a permanent part within the σθ = 24.5–26.5 Isopycnal Layer, with a semiannual cycle, known as the EUC, and a nonpermanent part in the deep thermocline (beneath σθ = 26.5 Isopycnal), associated with a strong eastward transport (up to 15 Sv) during the boreal summer, that is not observed during the rest of the year. The current at the equator in the deep thermocline is even westward during boreal fall. The disappearance of the salinity core of the EUC during the boreal summer, associated with the upwelling of the hydrological structure at 10°W, reveals that the saline subtropical waters carried by the EUC within the thermocline no longer flow into the Gulf of Guinea during the boreal summer. Our data also show the presence of the South Equatorial Undercurrent (SEUC) at 10°W in the Gulf of Guinea with a strong latitudinal and depth variability throughout the year. The mean SEUC at 10°W is centered near 5°S and is farther south than observed at 35°W and 26°W, suggesting its poleward shift from west to east.

Bernard Bourlès - One of the best experts on this subject based on the ideXlab platform.

  • Seasonal variability of the equatorial undercurrent termination and associated salinity maximum in the Gulf of Guinea
    Climate Dynamics, 2014
    Co-Authors: Nicolas Kolodziejczyk, Frédéric Marin, Bernard Bourlès, Yves Gouriou, Henrick Berger
    Abstract:

    The termination of the Equatorial Undercurrent (EUC) in the eastern equatorial Atlantic during boreal summer and fall, and the fate of the associated saline water masses, are analyzed from in situ hydrological and currents data collected during 19 hydrographic cruises between 2000 and 2007, complemented by observations from Argo profiling floats and PIRATA moorings, and from a numerical simulation of the Tropical Atlantic Ocean for the period 1993–2007. An intense variability of the circulation and hydrological properties is evidenced from observations in the upper thermocline (24.5–26.2 Isopycnal Layer) between June and November. During early boreal summer, saline water masses are transported eastward in the upper thermocline to the African coast within the EUC, and recirculate westward on both sides of the EUC. In mid-boreal summer, the EUC weakens in the upper thermocline and the equatorial salinity maximum disappears due to intense mixing with the surface waters during the upwelling season. The extra-equatorial salinity maxima are also partially eroded during the boreal summer, with a slight poleward migration of the southern hemisphere maximum until late boreal summer. The upper EUC reappears in September, feeding again the eastern equatorial Atlantic with saline waters until boreal spring. During December–January, numerical results suggest a second seasonal weakening of the EUC in the Gulf of Guinea, with a partial erosion of the associated equatorial salinity maximum.

  • Seasonal variability of the Equatorial Undercurrent at 10°W as inferred from recent in situ observations
    Journal of Geophysical Research, 2009
    Co-Authors: Nicolas Kolodziejczyk, Frédéric Marin, Bernard Bourlès, Jacques Grelet, Remy Chuchla
    Abstract:

    [1] Eighteen cross-equatorial shipboard current profiling sections along 10°W with conductivity-temperature-depth measurements taken between 1997 and 2007 are used to analyze the mean meridional structure and the seasonal variability of the Equatorial Undercurrent (EUC) at 10°W. Our analysis suggests a seasonal cycle for the EUC transport at 10°W, with a well-defined annual harmonic and some indication of a semiannual component, with a first maximum in January and a second stronger maximum from June to September. The mean EUC transport at 10°W is estimated to be 12.1 Sv and, compared to earlier estimates farther in the west, at 35°W (20.9 Sv) and 26°W (13.8 Sv). The eastward flow transport exhibits a strong variability at 10°W (with a total range of transports from 7.1 Sv to more than 31.7 Sv). The seasonal amplitude of the eastward flow variability is ±8.9 Sv, from a minimum of 8.2 Sv in November to 25.9 Sv in August. The eastward flows within the thermocline are divided in two parts: a permanent part within the σθ = 24.5–26.5 Isopycnal Layer, with a semiannual cycle, known as the EUC, and a nonpermanent part in the deep thermocline (beneath σθ = 26.5 Isopycnal), associated with a strong eastward transport (up to 15 Sv) during the boreal summer, that is not observed during the rest of the year. The current at the equator in the deep thermocline is even westward during boreal fall. The disappearance of the salinity core of the EUC during the boreal summer, associated with the upwelling of the hydrological structure at 10°W, reveals that the saline subtropical waters carried by the EUC within the thermocline no longer flow into the Gulf of Guinea during the boreal summer. Our data also show the presence of the South Equatorial Undercurrent (SEUC) at 10°W in the Gulf of Guinea with a strong latitudinal and depth variability throughout the year. The mean SEUC at 10°W is centered near 5°S and is farther south than observed at 35°W and 26°W, suggesting its poleward shift from west to east.

  • seasonal variability of the equatorial undercurrent at 10 w as inferred from recent in situ observations
    Journal of Geophysical Research, 2009
    Co-Authors: Nicolas Kolodziejczyk, Frédéric Marin, Bernard Bourlès, Jacques Grelet, Remy Chuchla
    Abstract:

    [1] Eighteen cross-equatorial shipboard current profiling sections along 10°W with conductivity-temperature-depth measurements taken between 1997 and 2007 are used to analyze the mean meridional structure and the seasonal variability of the Equatorial Undercurrent (EUC) at 10°W. Our analysis suggests a seasonal cycle for the EUC transport at 10°W, with a well-defined annual harmonic and some indication of a semiannual component, with a first maximum in January and a second stronger maximum from June to September. The mean EUC transport at 10°W is estimated to be 12.1 Sv and, compared to earlier estimates farther in the west, at 35°W (20.9 Sv) and 26°W (13.8 Sv). The eastward flow transport exhibits a strong variability at 10°W (with a total range of transports from 7.1 Sv to more than 31.7 Sv). The seasonal amplitude of the eastward flow variability is ±8.9 Sv, from a minimum of 8.2 Sv in November to 25.9 Sv in August. The eastward flows within the thermocline are divided in two parts: a permanent part within the σθ = 24.5–26.5 Isopycnal Layer, with a semiannual cycle, known as the EUC, and a nonpermanent part in the deep thermocline (beneath σθ = 26.5 Isopycnal), associated with a strong eastward transport (up to 15 Sv) during the boreal summer, that is not observed during the rest of the year. The current at the equator in the deep thermocline is even westward during boreal fall. The disappearance of the salinity core of the EUC during the boreal summer, associated with the upwelling of the hydrological structure at 10°W, reveals that the saline subtropical waters carried by the EUC within the thermocline no longer flow into the Gulf of Guinea during the boreal summer. Our data also show the presence of the South Equatorial Undercurrent (SEUC) at 10°W in the Gulf of Guinea with a strong latitudinal and depth variability throughout the year. The mean SEUC at 10°W is centered near 5°S and is farther south than observed at 35°W and 26°W, suggesting its poleward shift from west to east.

Frédéric Marin - One of the best experts on this subject based on the ideXlab platform.

  • Seasonal variability of the equatorial undercurrent termination and associated salinity maximum in the Gulf of Guinea
    Climate Dynamics, 2014
    Co-Authors: Nicolas Kolodziejczyk, Frédéric Marin, Bernard Bourlès, Yves Gouriou, Henrick Berger
    Abstract:

    The termination of the Equatorial Undercurrent (EUC) in the eastern equatorial Atlantic during boreal summer and fall, and the fate of the associated saline water masses, are analyzed from in situ hydrological and currents data collected during 19 hydrographic cruises between 2000 and 2007, complemented by observations from Argo profiling floats and PIRATA moorings, and from a numerical simulation of the Tropical Atlantic Ocean for the period 1993–2007. An intense variability of the circulation and hydrological properties is evidenced from observations in the upper thermocline (24.5–26.2 Isopycnal Layer) between June and November. During early boreal summer, saline water masses are transported eastward in the upper thermocline to the African coast within the EUC, and recirculate westward on both sides of the EUC. In mid-boreal summer, the EUC weakens in the upper thermocline and the equatorial salinity maximum disappears due to intense mixing with the surface waters during the upwelling season. The extra-equatorial salinity maxima are also partially eroded during the boreal summer, with a slight poleward migration of the southern hemisphere maximum until late boreal summer. The upper EUC reappears in September, feeding again the eastern equatorial Atlantic with saline waters until boreal spring. During December–January, numerical results suggest a second seasonal weakening of the EUC in the Gulf of Guinea, with a partial erosion of the associated equatorial salinity maximum.

  • Seasonal variability of the Equatorial Undercurrent at 10°W as inferred from recent in situ observations
    Journal of Geophysical Research, 2009
    Co-Authors: Nicolas Kolodziejczyk, Frédéric Marin, Bernard Bourlès, Jacques Grelet, Remy Chuchla
    Abstract:

    [1] Eighteen cross-equatorial shipboard current profiling sections along 10°W with conductivity-temperature-depth measurements taken between 1997 and 2007 are used to analyze the mean meridional structure and the seasonal variability of the Equatorial Undercurrent (EUC) at 10°W. Our analysis suggests a seasonal cycle for the EUC transport at 10°W, with a well-defined annual harmonic and some indication of a semiannual component, with a first maximum in January and a second stronger maximum from June to September. The mean EUC transport at 10°W is estimated to be 12.1 Sv and, compared to earlier estimates farther in the west, at 35°W (20.9 Sv) and 26°W (13.8 Sv). The eastward flow transport exhibits a strong variability at 10°W (with a total range of transports from 7.1 Sv to more than 31.7 Sv). The seasonal amplitude of the eastward flow variability is ±8.9 Sv, from a minimum of 8.2 Sv in November to 25.9 Sv in August. The eastward flows within the thermocline are divided in two parts: a permanent part within the σθ = 24.5–26.5 Isopycnal Layer, with a semiannual cycle, known as the EUC, and a nonpermanent part in the deep thermocline (beneath σθ = 26.5 Isopycnal), associated with a strong eastward transport (up to 15 Sv) during the boreal summer, that is not observed during the rest of the year. The current at the equator in the deep thermocline is even westward during boreal fall. The disappearance of the salinity core of the EUC during the boreal summer, associated with the upwelling of the hydrological structure at 10°W, reveals that the saline subtropical waters carried by the EUC within the thermocline no longer flow into the Gulf of Guinea during the boreal summer. Our data also show the presence of the South Equatorial Undercurrent (SEUC) at 10°W in the Gulf of Guinea with a strong latitudinal and depth variability throughout the year. The mean SEUC at 10°W is centered near 5°S and is farther south than observed at 35°W and 26°W, suggesting its poleward shift from west to east.

  • seasonal variability of the equatorial undercurrent at 10 w as inferred from recent in situ observations
    Journal of Geophysical Research, 2009
    Co-Authors: Nicolas Kolodziejczyk, Frédéric Marin, Bernard Bourlès, Jacques Grelet, Remy Chuchla
    Abstract:

    [1] Eighteen cross-equatorial shipboard current profiling sections along 10°W with conductivity-temperature-depth measurements taken between 1997 and 2007 are used to analyze the mean meridional structure and the seasonal variability of the Equatorial Undercurrent (EUC) at 10°W. Our analysis suggests a seasonal cycle for the EUC transport at 10°W, with a well-defined annual harmonic and some indication of a semiannual component, with a first maximum in January and a second stronger maximum from June to September. The mean EUC transport at 10°W is estimated to be 12.1 Sv and, compared to earlier estimates farther in the west, at 35°W (20.9 Sv) and 26°W (13.8 Sv). The eastward flow transport exhibits a strong variability at 10°W (with a total range of transports from 7.1 Sv to more than 31.7 Sv). The seasonal amplitude of the eastward flow variability is ±8.9 Sv, from a minimum of 8.2 Sv in November to 25.9 Sv in August. The eastward flows within the thermocline are divided in two parts: a permanent part within the σθ = 24.5–26.5 Isopycnal Layer, with a semiannual cycle, known as the EUC, and a nonpermanent part in the deep thermocline (beneath σθ = 26.5 Isopycnal), associated with a strong eastward transport (up to 15 Sv) during the boreal summer, that is not observed during the rest of the year. The current at the equator in the deep thermocline is even westward during boreal fall. The disappearance of the salinity core of the EUC during the boreal summer, associated with the upwelling of the hydrological structure at 10°W, reveals that the saline subtropical waters carried by the EUC within the thermocline no longer flow into the Gulf of Guinea during the boreal summer. Our data also show the presence of the South Equatorial Undercurrent (SEUC) at 10°W in the Gulf of Guinea with a strong latitudinal and depth variability throughout the year. The mean SEUC at 10°W is centered near 5°S and is farther south than observed at 35°W and 26°W, suggesting its poleward shift from west to east.