• Eddy-Kuroshio Interaction
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Conclusions:

We have sucessfully simulated the eddy-Kuroshio interaction observed in the satellite altimetric data (TOPEX/POSEIDON).  The T/P altimetric data was assimilated into a state-of-the-art GCM by means of OI-Nudging to initialize the anticyclonic eddy west of Izu Ridge.  The successive evolution of the simulated eddy and its interaction with the Kuroshio resembled the observed short-term Kuroshio meanders in 1993 and 1998 that are known to have induced by an anticyclonic eddy.   The simulated model outputs were analyzed to study the various stages of the interaction: i) collision between the westward propagating eddy and the Kuroshio near Kyushu; ii) advection of the eddy by the Kuroshio and meander formation; iii) detachment of the eddy from the Kuroshio; iv) westward propagation of the eddy and then repetition of stages i) and ii).

The sequence described above may be repeated several times in nature; in the simulation the meander occured twice.

When the eddy approaches the Kuroshio at a lower latitude, it collides with the Kuroshio near Kyushu and causes the Kuroshio to separate below Yaku-shima  (1st collision).  As a result of the flow separation, a cyclonic eddy is shed along the coast and moves with the anticyclonic eddy.  The presence of this cyclonic eddy changes the angle of attack of the Kuroshio flow against Kii Peninsula and another cyclonic eddy is shed at Shiono-misaki.   These cyclonic eddies eventually join the separation bubble (the cyclonic eddy that usually exists between the Kii Peninsula and the Izu Ridge) and a meander starts to grow.  As the meander grows, the anticyclonic eddy develops a number of neighboring eddies, energy transfers among them, and eventually they join into a single eddy.  As the thermocline displacement of the eddy grows, the eddy detaches itself from the Kuroshio, presumably due to its own thrust, moves westward until additional thrust is added through advection by the lower-layer geostrophic motion.  The second collision of the anticyclonic eddy with the Kuroshio near Kyushu occurs north of the first encounter, and this time, no flow separation is observed along the Kyushu coast.  The eddy advects downstream and a second meander occurs.

We have also shown an example of an anticyclonic eddy generation in the Kuroshio Extension region.  As the meander develops, anticyclonic eddies are formed south of the Kuroshio Extension.  These eddies merge, forming a larger eddy (in a process similar to an inverse energy cascade) and the eddy, driven by the lower-layer geostrophic motion, detaches itself from the Kuroshio .  This detachment process differs from the case described above.