| Co-Investigator(Kenkyū-buntansha) |
OSHIMA Keiichiro Hokkaido University, Inst. Low Temp. Sci., Asso. Prof. (30185251)
NAKAMURA T. Hokkaido University, Inst. Low Temp. Sci., Lecturer (60400008)
ONO K. Hokkaido University, Inst. Low Temp. Sci., Technical Staff (40396320)
NISHIGAKI H. Oita University, Faculty Edu. Wel Sci., Lecturer (70253763)
内本 圭亮 北海道大学, 低温科学研究所, 非常勤研究員 (10374646)
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| Budget Amount *help |
¥3,500,000 (Direct Cost: ¥3,500,000)
Fiscal Year 2006: ¥1,700,000 (Direct Cost: ¥1,700,000)
Fiscal Year 2005: ¥1,800,000 (Direct Cost: ¥1,800,000)
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| Research Abstract |
Clockwise circulations are dominant in the Kuril Basin, the southern portion of the Sea of Okhotsk. Correspondingly, potential vorticity (PV) in the intermediate layer is low in this region. In this project, formation processes of the clockwise circulation were investigated.
First, effects of localized mixing around the Kuril Islands were considered. A two-layer model with a submarine ridge was used, and mixing is parameterized as diapycnal vertical velocity over the ridge topography. When the mixing commences, the interface deepens over the ridge locally. For weak mixing cases, the depth of the interface corresponds well to a linear beta-plume solution. If the mixing becomes stronger, low PV water forms first over the ridge. Then, the low PV water is carried westward by eddies and waves, letting low PV water occupy the entire region west of the ridge. It is noted that the lower layer flow around the ridge gives significant influences on the circulation through modifying characteristics
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of the upper-layer wave. In particular, if the characteristics have closed contours, then PV input due to vertical velocity is hardly radiated from the topographic region until the interface becomes so deep that baroclinic instability can take place. Bimodal states in the clockwise circulation are found.
Second, a high resolution Okhotsk Sea Model, with a 1/12 degree horizontal resolution, was used to investigate wind-driven circulation. The clockwise circulation in the Kuril Basin is formed as a recirculation gyre associated with an eastward jet that extends from the East Sakhalin Current. Both the numerical results and the altimeter data from satellites indicate that this circulation has an annual signal corresponding to the annual variations in wind-stress.
From these experiments, it has been found that the clockwise circulation in the Sea of Okhotsk has rich structures incorporating both wind-driven and thernmohaline components. An analytical model that investigates impacts on the intermediate layer circulation was also constructed. Further, analysis of data from the intensive CTD survey across the Bussol' Strait were carried out to estimate the vertical mixing strength along the Kuril Islands. Less
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