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 boundary currents, using a simple two-layer quasi-geostrophic (QG) model forced by a wind stress curl consistent with the formation of a subtropical gyre. The dependency of the latitude of the eastward jet on various parameters and on the meridional distribution of the Ekman pumping velocity was investigated. The parameters considered in the present study included the viscous and inertial western boundary layer width, the parameter representing the degree of the partial slip boundary condition, the ratio of the upper to the lower layer depth, and the bottom friction. With the parameters used, two types of stable structures are found in the time mean field. One type of structure represented the ‘prematurely separated jet case’, in which the eastward extension jet was located far south 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 along the northern boundary. The initial condition decides which type of structure would occur. When the prematurely separated jet case occurred the latitude of the eastward jet depended very little on the parameters. In addition, the latitude was determined by the meridional distribution of the Ekman pumping velocity. The eastward extension jet was usually located near the latitude that was half of the maximum value of the Sverdrup streamfunction and satisfied an integral condition derived from the QG potential vorticity equation.
Hokkaido University(北海道大学). 博士(環境科学)

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