1998 Fiscal Year Final Research Report Summary
Studies on oceanic eddies in the Northwestern Subarctic Pacific
| Project/Area Number |
09640515
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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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 | The University of Tokyo |
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Principal Investigator |
YASUDA Ichiro The University of Tokyo, Graduate School of Science, Associate Professor, 大学院・理学系研究科, 助教授 (80270792)
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| Project Period (FY) |
1997 – 1998
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| Keywords | North Pacific / Western Subarctic Gyre / North Pacific Intermediate Water / vortex / Oyashio |
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| Research Abstract |
Summer hydrographic surveys from 1993 to 1997 in the area south of Kuril Islands in the northwestern Subarctic Pacific showed theexistence of anticyclonic eddies south of the Bussol' Strait at almost the same location but with variable sizes and intensities depending on the year. Every eddy had a cold, low-salinity and low-potential vorticity core, suggesting a strong influence from the Okhotsk Sea water. Two formation processes and annual variations were found with satellite data analyses. One is the case where eddies are locally formed south of the Bussol' Strait and intensified from summer to fall with the supply of Okhotsk Sea water as observed in 1993. In the other case, Kuroshio warm-core rings that had translated north-eastward are arrested near the Bussol' Strait and amplified with the supply of Okhotsk Sea water as seen from summer to autumn in 1995. In winter, eddies tend to move north-eastward with decay. 1992-eddy moved northeastward then northward in winter, and was eventually absorbed into the East Kamchatska Current. Mechanisms of the northeastward movements and the formations of the Bussol' eddies were discussed. Pseudo-beta effect due to deep north-eastward currents along the Kuril-Kamchatka Trench could be responsible for the northeastward movement. Since the volume transport of the coastal Oyashio water along the southern Kuril Islands is constrained by the potential vorticity difference between the Okhotsk Sea and the western Subarctic Gyre (WSAG), eddies could be generated and intensified when a outflow rate from the Okhotsk Sea exceeds the critical transport. The observed annual variations of the eddy evolutions might be explained by the critical transport variation associated with an annual change of the WASG.
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