Interpretation of Repulsive Bifurcation of the Kuroshio and Gulf Stream with Classification of Their Branches |
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| Authors: | Hideo Kawai |
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| Institution: | (1) 131-81 Shibagahara, Kuse, Joyo, Kyoto Pref 610-0102, Japan |
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| Abstract: | Distinctive features of the repulsive bifurcation of Kuroshio and Gulf Stream jets, induced from various observations, have
been examined by equations of motion of a 1 1/2 -layer model in natural coordinates, although causes of the bifurcation are
discussed little. From the conservation of volume flux through paths above a main thermocline, we have derived the equation
M
n
K
In + M
s
K
Is = 0 for northern (n) and southern (s), steady-state curved jets, just downstream of the bifurcation from a straight jet, where M is momentum flux through the path and K
I, positive for cyclonic deflection of the streamline, is the curvature of a certain intermediate streamline in the laminar
path. Assuming concentric streamlines in the curved path, which is narrower than 1–0.5 times the radius of curvature of the
center streamline of the path, and symmetric momentum flux through a path element of unit width with respect to the center
streamline, we found that K
I approximates to the curvature averaged across the path, relative errors being <0.25−(0.25)2. Bifurcation starts with a ‘Big Bang’ and the leading turbulent front of a split jet may be unsteady, but the succeeding
laminar part can be regarded as stationary or as translating at a constant velocity, as if frozen. Thus, such features are
described by the equation. A provisional classification is given of various warm extrusions along branches of both Streams,
all of which exemplify the repulsive bifurcation, except for the mainstreams with very narrow (< 30–40 km) branches, possibly
due to misapplication of the model.
This revised version was published online in August 2006 with corrections to the Cover Date. |
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| Keywords: | Repulsive bifurcation Kuroshio Gulf Stream branch natural coordinates momentum flux secondary front warm streamer warm tongue warm outbreak |
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