Kuroshio Transport: Inter-annual to Decadal Variability and the Underlying Mechanisms

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Previous observational studies have highlighted a delay in Kuroshio transport variability relative to basin-scale atmospheric forcing, and thus have emphasized baroclinic Rossby wave adjustment as the mechanism by which remote forcing reaches the western boundary. However, recent observational studies and preliminary analyses suggest that, in fact, the Kuroshio and its extension each exhibit both delayed and immediate responses to the atmospheric forcing, suggesting that additional mechanisms play important roles in Kuroshio variability. The project will take a comprehensive look at these two response time scales, paying particular attention to the rapid response and to the connectivity of the components comprising the North Pacific subtropical gyre. The purpose of this study is to develop a better understanding of how the ocean responds to basin-scale wind forcing, especially in the western boundary currents and their extensions, with a focus on interannual to decadal variability in the Kuroshio system. In the North Pacific, such variability manifests itself in the Pacific Decadal Oscillation (PDO), a climate index reflecting the large-scale sea surface temperature variability, which is also well-correlated with the leading mode of wind stress curl variability over the most recent decades.A combination of existing observational data, idealized numerical model experiments, and output from an eddy-resolving ocean general circulation model (OGCM) will be used to accomplish three goals: (1) characterize the interannual to decadal variability in the Kuroshio in the East China Sea (ECS-Kuroshio), (2) investigate the relative roles of local versus remote atmospheric forcing on the barotropic and baroclinic oceanic responses in the ECS-Kuroshio and identify waveguide(s) by which remote forcing reaches the ECS-Kuroshio, and (3) relate the variability in the ECS-Kuroshio to variability in other parts of the subtropical gyre circulation, especially that in the Kuroshio Extension region.Intellectual Merit: The combined use of observations, a two-layer model, and ocean general circulation models output will lead to a more complete description of the Kuroshio system and a better understanding of the dynamics which give rise to variability in the western boundary current and its extension. Advancing the current understanding of the relationship between the inter-annual to decadal variability of ocean circulation and atmospheric forcing will be beneficial to the broader climate research community, particularly in the on-going community effort to improve inter-annual to decadal predictability.Broader Impacts: The first year of this project will partially support the postdoctoral training of the lead investigator, a junior scientist from an under-represented group. In addition, the lead investigator will perform outreach work with middle school students and their science teachers. This volunteer work will support the efforts of a school in Rhode Island to implement a 2009 Science and Math Scholars (SAMS) grant by NASA to improve the quality of science and math education in middle schools.