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[1] A long-lived (2-year) typical large meander (LM) path of the Kuroshio is reproduced in a high-resolution general circulation model (GCM) simulation with realistic topography, and the life cycle (formation, maintenance, and disappearance) of the LM is studied. The formation of the LM is triggered by a pair of upper layer anticyclonic and cyclonic eddies on the Kuroshio, with the cyclonic one on the downstream side. Upon reaching the western side of the Shikoku Basin south of Japan these anomalies induce a lower layer anticyclonic eddy. They enhance each other while they are carried eastward by the Kuroshio. Specifically, the southward flow on the eastern side of the lower anticyclonic eddy carries the upper cold cyclonic eddy offshore, resulting in the southward deflection of the Kuroshio path (large meander). These processes can be understood as a growth of baroclinic instability. A stationary LM is established when the westward tendency, caused by the beta effect owing to the large meridional displacement, counterbalances the eastward tendency, caused by the combination of advection and vortex induction owing to the curvature of the Kuroshio path. Large-scale disturbances from the upstream tend to strengthen the LM through baroclinic energy conversion. In contrast, small-scale disturbances from the upstream grow locally along the meandering Kuroshio front through baroclinic energy conversion. They extract cold waters from the cold cyclonic eddy of the LM as they flow away to the east. The horizontal extent of the cold cyclonic eddy is reduced, and the meander is carried eastward since the advection effect dominates over the beta effect that weakens as a result of the smaller meridional extent.

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Abstract. This study uses a neural network technique to produce maps of the partial pressure of oceanic carbon dioxide (pCO2sea) in the North Pacific on a 0.25° latitude × 0.25° longitude grid from 2002 to 2008. The pCO2sea distribution was computed using a self-organizing map (SOM) originally utilized to map the pCO2sea in the North Atlantic. Four proxy parameters – sea surface temperature (SST), mixed layer depth, chlorophyll a concentration, and sea surface salinity (SSS) – are used during the training phase to enable the network to resolve the nonlinear relationships between the pCO2sea distribution and biogeochemistry of the basin. The observed pCO2sea data were obtained from an extensive dataset generated by the volunteer observation ship program operated by the National Institute for Environmental Studies (NIES). The reconstructed pCO2sea values agreed well with the pCO2sea measurements, with the root-mean-square error ranging from 17.6 μatm (for the NIES dataset used in the SOM) to 20.2 μatm (for independent dataset). We confirmed that the pCO2sea estimates could be improved by including SSS as one of the training parameters and by taking into account secular increases of pCO2sea that have tracked increases in atmospheric CO2. Estimated pCO2sea values accurately reproduced pCO2sea data at several time series locations in the North Pacific. The distributions of pCO2sea revealed by 7 yr averaged monthly pCO2sea maps were similar to Lamont-Doherty Earth Observatory pCO2sea climatology, allowing, however, for a more detailed analysis of biogeochemical conditions. The distributions of pCO2sea anomalies over the North Pacific during the winter clearly showed regional contrasts between El Niño and La Niña years related to changes of SST and vertical mixing.

many of the coupled ocean-atmosphere global circulation models in the coming decade will represent oceanic fronts reasonably well, and it is hoped that this review along with the table of metrics will provide a useful benchmark for evaluating these models.