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    A Numerical Investigation of the Subduction Process in Response to an Abrupt Intensification of the Westerlies

    Source: Journal of Physical Oceanography:;1999:;Volume( 029 ):;issue: 008::page 1993
    Author:
    Inui, Tomoko
    ,
    Takeuchi, Kensuke
    ,
    Hanawa, Kimio
    DOI: 10.1175/1520-0485(1999)029<1993:ANIOTS>2.0.CO;2
    Publisher: American Meteorological Society
    Abstract: A three-dimensional ocean general circulation model, forced by idealized zonal winds, is used to investigate the effect of an abrupt intensification of westerly winds on the subduction process. Four experiments are carried out: 1) a control experiment with standard wind stress forcing, 2) an intensified winds experiment with wind stress that is larger in the region of the westerlies than the control, 3) an increased surface cooling experiment, and 4) an experiment with both intensified wind stress and surface cooling. Experiments 2 through 4, which contain surface anomalous forcing, are run from the steady state obtained in experiment 1, the control experiment. The results obtained for each of these runs are compared to the control experiment. A subarctic tracer injection experiment is also carried out to verify the differences in the subduction process of each of these experiments. In the wind stress intensified experiment, an examination of the subsurface temperature field shows that negative temperature anomalies occupy the western portion of the southern part of the subtropical gyre, whereas in the surface cooling experiment, negative temperature anomalies occupy the eastern portion of the basin. The source of these negative temperature anomalies is not local since the forcing in the southern part of the subtropical gyre does not change from the control. A close analysis of the evolution of a subarctic surface tracer field indicates that the intensification of the wind stress increases the tracer concentrations, whereas surface cooling decreases the temperature in the region that contains the maximum tracer concentration. In the standard case, the mixed layer is deep (shallow) in the northern (southern) part of the subtropical gyre. Between these two regions a mixed layer front, where the mixed layer depth changes drastically from north to south, exists. A water column with low potential vorticity that originates in the mixed layer penetrates into a subsurface layer from the point where an outcrop line and the mixed layer front intersect. This point is called the penetration point. Intensified westerly winds bring about a deeper thermocline and shoaling subsurface isopycnals. These shoaling subsurface isopycnals are not predicted in classical models such as that of Luyten et al. The model experiment with intensified westerlies demonstrates that the penetration point shifts to the west. As a result, low potential vorticity water penetrates southwestward from the shifted penetration point and takes a more westward path. Therefore, the negative temperature anomalies appear in the southwestern part of the subtropical gyre. This study shows that the westward shift of the path of low potential vorticity water could cause the shoaling of subsurface isopycnal surfaces. The intensification of the westerlies increases Ekman pumping and cools the ocean surface by enhancing sensible and latent heat flux. In the surface cooling experiment, the position of the outcrop lines moves southward significantly. This southward shift makes the subducted water colder and distributes it throughout the ventilated region of the southern part of the subtropical gyre. The combined effect of wind intensification and surface cooling is approximately a linear combination of both experiments.
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      A Numerical Investigation of the Subduction Process in Response to an Abrupt Intensification of the Westerlies

    URI
    http://yetl.yabesh.ir/yetl1/handle/yetl/4166280
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    • Journal of Physical Oceanography

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    contributor authorInui, Tomoko
    contributor authorTakeuchi, Kensuke
    contributor authorHanawa, Kimio
    date accessioned2017-06-09T14:53:36Z
    date available2017-06-09T14:53:36Z
    date copyright1999/08/01
    date issued1999
    identifier issn0022-3670
    identifier otherams-29091.pdf
    identifier urihttp://onlinelibrary.yabesh.ir/handle/yetl/4166280
    description abstractA three-dimensional ocean general circulation model, forced by idealized zonal winds, is used to investigate the effect of an abrupt intensification of westerly winds on the subduction process. Four experiments are carried out: 1) a control experiment with standard wind stress forcing, 2) an intensified winds experiment with wind stress that is larger in the region of the westerlies than the control, 3) an increased surface cooling experiment, and 4) an experiment with both intensified wind stress and surface cooling. Experiments 2 through 4, which contain surface anomalous forcing, are run from the steady state obtained in experiment 1, the control experiment. The results obtained for each of these runs are compared to the control experiment. A subarctic tracer injection experiment is also carried out to verify the differences in the subduction process of each of these experiments. In the wind stress intensified experiment, an examination of the subsurface temperature field shows that negative temperature anomalies occupy the western portion of the southern part of the subtropical gyre, whereas in the surface cooling experiment, negative temperature anomalies occupy the eastern portion of the basin. The source of these negative temperature anomalies is not local since the forcing in the southern part of the subtropical gyre does not change from the control. A close analysis of the evolution of a subarctic surface tracer field indicates that the intensification of the wind stress increases the tracer concentrations, whereas surface cooling decreases the temperature in the region that contains the maximum tracer concentration. In the standard case, the mixed layer is deep (shallow) in the northern (southern) part of the subtropical gyre. Between these two regions a mixed layer front, where the mixed layer depth changes drastically from north to south, exists. A water column with low potential vorticity that originates in the mixed layer penetrates into a subsurface layer from the point where an outcrop line and the mixed layer front intersect. This point is called the penetration point. Intensified westerly winds bring about a deeper thermocline and shoaling subsurface isopycnals. These shoaling subsurface isopycnals are not predicted in classical models such as that of Luyten et al. The model experiment with intensified westerlies demonstrates that the penetration point shifts to the west. As a result, low potential vorticity water penetrates southwestward from the shifted penetration point and takes a more westward path. Therefore, the negative temperature anomalies appear in the southwestern part of the subtropical gyre. This study shows that the westward shift of the path of low potential vorticity water could cause the shoaling of subsurface isopycnal surfaces. The intensification of the westerlies increases Ekman pumping and cools the ocean surface by enhancing sensible and latent heat flux. In the surface cooling experiment, the position of the outcrop lines moves southward significantly. This southward shift makes the subducted water colder and distributes it throughout the ventilated region of the southern part of the subtropical gyre. The combined effect of wind intensification and surface cooling is approximately a linear combination of both experiments.
    publisherAmerican Meteorological Society
    titleA Numerical Investigation of the Subduction Process in Response to an Abrupt Intensification of the Westerlies
    typeJournal Paper
    journal volume29
    journal issue8
    journal titleJournal of Physical Oceanography
    identifier doi10.1175/1520-0485(1999)029<1993:ANIOTS>2.0.CO;2
    journal fristpage1993
    journal lastpage2015
    treeJournal of Physical Oceanography:;1999:;Volume( 029 ):;issue: 008
    contenttypeFulltext
    DSpace software copyright © 2002-2015  DuraSpace
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    DSpace software copyright © 2002-2015  DuraSpace
    نرم افزار کتابخانه دیجیتال "دی اسپیس" فارسی شده توسط یابش برای کتابخانه های ایرانی | تماس با یابش
    yabeshDSpacePersian