Kuroshio and recirculation gyres
Humio Mitsudera
International Pacific Research Center, Honolulu, Hawaii
It is well known that the Gulf Stream has strong recirculation gyres adjacent to the stream. In recent observations, it has also been shown that the Kuroshio has well-defined recirculation gyres off the southern coast of Japan and in the Kuroshio extension area, whose transport sometimes exceeds 100Sv. Intra-annual oscillation with about 100 day period is evidenced from the TOPEX/POSEIDON and current measurement off the south coast of Japan. Our recent numerical model results indicate that the recirculation and its variations influence the Kuroshio path strongly, whether it takes meandering or straight one. When the meandering path is taken, the gyre is strongly spun up, having the homogeneous potential vorticity inside. Further, the recirculation gyre has a barotropic structure.
The recirculation gyre in the Kuroshio extension has been observed by LADCP during WOCE period. The recirculation has a transport about 70Sv, which makes the eastward Kuroshio extension transport more than 120Sv. This is comparable to those observed with the Gulf Stream. Further, the vertical structure is dominantly barotropic there.
These indicate that the barotropic component is very important for the recirculation gyres in the Kuroshio and its extension area. Acoustic tomography is suitable tool to measure barotropic current. Further, the recirculation gyres are hypothesized to be driven by eddy flux convergence, which is also an appropriate parameter to be observed by the acoustic tomography system.