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Young-Ho Seung

Abstract

The generation mechanism for a wintertime cyclonic gyre in the western Labrador Sea, first observed by Clarke and Gascard, is studied by using simple theoretical models. It is shown that atmospheric cooling, which occurs during outbreaks of cold, dry continental air, can be localized by air modification induced by oceanic heat and water vapor transport. The resulting scale of cooling is comparable to the cross-shore scale of the observed gyre. The density structure of the underlying water mass is then altered by this localized cooling and also by horizontal mixing. The model results compare reasonably well with observations. Finally, it is demonstrated that the observed gyre may be generated when the new density structure adjusts itself to geostrophic equilibrium.

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Sok Kuh Kang, Young Ho Seung, Jong Jin Park, Jae-Hun Park, Jae Hak Lee, Eun Jin Kim, Young Ho Kim, and Moon-Sik Suk

Abstract

Trajectories of Argo floats deployed in the East/Japan Sea from 2001 to 2014 reveal that the middepth gyral circulation pattern of the Japan basin, the central part of the East/Japan Sea, undergoes a seasonal variation. The middepth circulation of the Japan basin is found to be characterized usually by the gyres trapped to the east of the Bogorov Rise (E-gyres) and those extending farther westward into the whole basin (BW-gyres). The E-gyre trajectories are generally associated with the turning of the floats toward deeper regions off the isobaths. This occurs in winter either on the northern or eastern side of the eastern Japan basin. It seems that the upstream part of the otherwise BW-gyre is subject to a strong negative wind stress curl in winter, and there the circulating water columns are driven toward the deeper region, thus triggering the formation of the E-gyre. The topographic effect associated with the Bogorov Rise seems to interfere thereafter in the process of determining the passage of the E-gyre. Otherwise, the water columns continue to flow along the isobaths, hence maintaining the BW-gyre. To the knowledge of the authors, this is the first observational evidence of seasonal variability in the middepth gyral circulation pattern in the East/Japan Sea. It suggests that oceanic middepth circulation, usually known to be quasi steady or slowly varying on climatological time scales, might also undergo a significant seasonal variation as it does in the East/Japan Sea.

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