2001 Fiscal Year Final Research Report Summary
Analysis of heat transport driven by the Kuroshio and short-range forecast of the Kuroshio variabilities using data assimilation methods
| Project/Area Number |
11440140
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Meteorology/Physical oceanography/Hydrology
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| Research Institution | KYOTO UNIVERSITY |
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Principal Investigator |
AWAJI Toshiyuki Kyoto Univ. Dept.of Geophysics Professor, 大学院・理学研究科, 教授 (40159512)
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| Co-Investigator(Kenkyū-buntansha) |
ISHIKAWA Yoichi Kyoto Univ. Dept.of Geophysics research associate, 大学院・理学研究科, 助手 (70335298)
KONDA Masanori Kyoto Univ. Dept.of Geophysics research associate, 大学院・理学研究科, 助手 (10273434)
AKITOMO Kazunori Kyoto Univ. Dept.of Geophysics Associate Professor, 大学院・理学研究科, 助教授 (10222530)
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| Project Period (FY) |
1999 – 2001
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| Keywords | Kuroshio / forecast / heat transport / data assimilation |
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| Research Abstract |
Capability for short-range forecasting of the Kuroshio path variabilities south of Japan is studied by assimilating the absolute sea surface dynamic height data into a high-resolution 1 1/2-layer primitive equation model for 5 years from 1993 to 1997. The initialisation scheme used is the variational method, which contains the nonlinear dynamics of the model as a weak constraint and is suitable for initialization in the western boundary current regions.
The time series of the analysis field well represents the-Kuroshio path variations during the study period For example, the rms differences from the observations falls within 0.3°for the location in latitude of the current axis off Enshu-nada while their observed rms variability is 0.5°
By using the resulting fields as the initial conditions, one hundred and sixteen cases of 90-day forecast experiments for the Kuroshio path variations are then performed to assess the statistical properties of our assimilation system. The accuracy of our f
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orecasted field south of Japan is much higher than that of persistence experiments and the typical evolution of the Kuroshio into a large-amplitude path off Enshu-nada is successfully reproduced after the initialization. In particular, the eastward progression speed and the horizontal scale of the meander are quite similar to those observed. These results and the comparison with the rms variability of the analysis field enable us to infer that roughly 60-day forecasts of the Kuroshio path variabilities south of Japan are possible.
Next, in order to estimate the total heat transport by the Kuroshio, we have constructed a 4D-VAR ocean data assimilation system using an ocean general circulation model and the adjoint method. The result demonstrates the validity of this reanalysis data. For example, the Kuroshio path is corrected to be more realistic and the surface heat flux reanalysis data in the Pacific Ocean represents most of the familiar gross features of past studies. These improvements allow us to estimate the Kuroshio heat transport adequately by our data assimilation system. Less
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