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Hideyuki Nakano Hiroyuki Tsujino Mikitoshi Hirabara Tamaki Yasuda Tatsuo Motoi Masao Ishii Goro Yamanaka 《Journal of Oceanography》2011,67(6):765-783
The uptake mechanism of anthropogenic CO2 in the Kuroshio Extension is examined by a Lagrangian approach using a biogeochemical model embedded in an ocean general circulation model. It is found that the uptake of anthropogenic CO2 is caused mainly by the increase of pCO2 dependency of seawater on temperature, which is caused by greater dissolved inorganic carbon concentration in the modern state than in the pre-industrial state. In contrast with the view of previous studies, the effect of the vertical entrainment, which brings waters that last contacted the atmosphere with the past lower CO2 concentration, is comparatively small. Winter uptake of anthropogenic CO2 increases with the rise of the atmospheric CO2 level, while summer uptake is relatively stable, resulting in a larger seasonal cycle of the uptake. This increase is significant, especially in the Kuroshio Extension region. It is newly suggested that this increase in the Kuroshio Extension region is largely caused by the combined effects of the increased pCO2 dependency of the sea water on the temperature and the seasonal difference in cooling. 相似文献
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Mikitoshi Hirabara Hiroyuki Tsujino Hideyuki Nakano Goro Yamanaka 《Journal of Oceanography》2012,68(5):771-796
An experiment using a global ocean–ice model with an interannual forcing data set was conducted to understand the variability in the Southern Ocean. A winter-persisting polynya in the Weddell Sea (the Weddell Polynya, WP) was simulated. The process of WP breaking out after no-WP years was explored using the successive WPs found in the late 1950s. The results suggested that the anomalously warm deep water, saline surface layer, and a cyclonic wind stress over the Maud polynya region in early winter are essential for the surface layer to be dense enough to trigger deep convections which maintain a winter-persisting polynya; also, the reanalyzed surface air temperature (SAT) over the observed polynya region is too high for an ocean–ice model’s bulk formula to yield sufficient upward heat fluxes to induce WP formation. Therefore the Weddell Polynya, a series of WPs observed from satellite in the mid-1970s, is reproduced by replacing the SAT with a climatological one. Subsequent to the successive WP events, density anomalies excited in the Weddell Sea propagate northward in the Atlantic deep basins. The Antarctic Circumpolar Current (ACC) is enhanced through the increased meridional density gradient. The enhanced ACC and its meandering over the abyssal ridges excite buoyancy anomalies near the bottom at the southwestern end of the South Pacific basin. The buoyancy signals propagate northward and eventually arrive in the northern North Pacific. 相似文献
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Hiroyuki Tsujino Mikitoshi Hirabara Hideyuki Nakano Tamaki Yasuda Tatsuo Motoi Goro Yamanaka 《Journal of Oceanography》2011,67(4):449-479
A long-term spin-up and a subsequent interannual simulation are conducted for the ocean–ice component of the climate model
intercomparison project (CMIP)-class earth system model of the Japan Meteorological Agency/Meteorological Research Institute.
This experiment has three purposes: first is to assess the ability of our model with the Coordinated Ocean–ice Reference Experiments
(COREs) forcing in reproducing the present ocean-climate; second is to understand the ocean-climate variability for the past
60 years; third is to present an example of evaluating an ocean–ice interannual variability simulation. The Pacific Ocean
is focused on for the last two purposes. After integrating for about 1500 years with repeated use of a detrended CORE interannual
forcing, the model reaches a quasi-steady state where the present climate is reproduced satisfactorily. Then, the interannual
variability simulation is conducted with the retrieved forcing trend and the result is analyzed. The simulation is successful
at reproducing the long-term variability in the Pacific and surrounding oceans. Brief analyses of the tropical and mid-latitude
upper layer, deep circulation, and the Arctic sea ice are presented. A caveat in treating other parts of the globe is due
to the recent intense convection in the Southern Ocean caused by a remarkably increasing trend of the Southern Hemisphere
westerly. Overall, the current simulation with our CMIP-class ocean–ice model is shown to be useful for studying the present
ocean-climate variability, specifically in the Pacific sector. It could also be used as a benchmark control experiment that
facilitates further research, model development, and intercomparison. 相似文献
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Mikitoshi Hirabara Hiroshi Ishizaki Goro Yamanaka Hiroyuki Tsujino Ichiro Ishikawa 《Journal of Oceanography》2010,66(5):633-647
An analysis is presented of snapshot data (eastward and northward velocity components: u and v; tracer such as potential temperature: τ) from an eddy-resolving (Rgrid: 1/12°) ocean model experiment, in order to explore a method for improving eddy-permitting
model performance. Horizontal 3 × 3 R-grid averages give the eddy-permitting grid (P-grid: 1/4°) variables: 〈u〉, 〈v〉, and 〈τ〉, where 〈〉 denotes the spatial P-grid scale average. The difference between the horizontal tracer flux across the boundary
face of a P-grid and that across the corresponding faces of R-grids is estimated as F2E. It is found that the correlations among the gradients of u, v, and τ give a good approximation F2C to the estimated flux F2E. The approximated flux is a function of these gradients and the grid size. A method is presented for implementing the F2C for density to an eddying ocean model as an additional advection. Practical experiments were conducted with a realistic configuration.
It is shown that the zonal mean isotherms in the Kuroshio extension region are more flattened in the run using the proposed
method than in another run using the conventional horizontal biharmonic operator, suggesting that the additional flux correction
leads to an enhancement of sub-basin scale mixing. 相似文献
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