Thesis or Dissertation A study on the latitude of a western boundary current extension jet

陶, 泰典

This thesis investigates the formation of eastward jets extended from western boundarycurrents, using a simple two-layer quasi-geostrophic (QG) model forced by a wind stresscurl consistent with the formation of a subtropical gyre. The dependency of the latitudeof the eastward jet on various parameters and on the meridional distribution of theEkman pumping velocity was investigated. The parameters considered in the presentstudy included the viscous and inertial western boundary layer width, the parameterrepresenting the degree of the partial slip boundary condition, the ratio of the upper tothe lower layer depth, and the bottom friction. With the parameters used, two typesof stable structures are found in the time mean field. One type of structure representedthe ‘prematurely separated jet case’, in which the eastward extension jet was located farsouth of the northern boundary of the subtropical gyre, as is the Kuroshio Extension;the other type was the ‘gyre boundary jet case’, in which the eastward jet occurred alongthe northern boundary. The initial condition decides which type of structure wouldoccur. When the prematurely separated jet case occurred the latitude of the eastward jetdepended very little on the parameters. In addition, the latitude was determined by themeridional distribution of the Ekman pumping velocity. The eastward extension jet wasusually located near the latitude that was half of the maximum value of the Sverdrupstreamfunction and satisfied an integral condition derived from the QG potential vorticityequation.
Hokkaido University(北海道大学). 博士(環境科学)

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