- 著者
- Fang Xiaorong Isoda Yutaka
- 出版者
- 北海道大学大学院水産科学研究院
- 雑誌
- 北海道大学水産科学研究彙報 (ISSN:24353353)
- 巻号頁・発行日
- vol.70, no.1, pp.25-40, 2020-08-24
A multi-layered numerical model driven by seasonal change in sea surface heat flux with excess cooling was used to investigate the dynamics of a cooling induced current (CIC) in the Japan Sea. The original idea of the CIC was proposed by Isoda (1999) (Journal of Oceanography, 55, 585-596) as follows : eastward thermal flow in the interior region, i.e., Tsushima Warm Current (TWC), accompanied with meridional thermal gradient on the planetary-β plane would be determined by the heat balance between net heat loss at the sea surface and lateral heat transport from the southern entrance into the Japan Sea. The CIC model produced a significant meandering TWC with an east-west wave number of three, based on the property of a standing Rossby wave, only under the model condition that coexisted with seasonal disturbances of heat. A positive heat supply from the southern entrance to the Japan Sea occurred in late winter, extended slowly to the TWC region as the offshore advection of meandering patchiness in summer, and then contributed to the heat loss by sea surface cooling in the following winter. The whole TWC region was cooled not only at the sea surface in winter, but also by eastward advection of upwelled cold waters originating from the western boundary area in summer to autumn. The meandering flow was stably confined to the southern part because of the dominant southward eddy momentum fluxes, which were caused by the northwest-southeast inclinations of meandering ridge-axes. Owing to such seasonal change in the lateral transports of momentum and heat, the meandering TWC (or CIC) flow pattern was maintained as a “dynamic equilibrium state”.
- 著者
- Matsuura Hiromi Isoda Yutaka
- 出版者
- 北海道大学大学院水産科学研究院
- 雑誌
- 北海道大学水産科学研究彙報 (ISSN:24353353)
- 巻号頁・発行日
- vol.70, no.1, pp.13-23, 2020-08-24
We examine the reason why non-equilibrium response of lunar fortnightly tide, i.e., Mf tide with 13.7-day period, dominates in the Japan/East Sea including the Tsugaru Strait. In the present study, tides combining with passage-flow through the (Tsugaru) Strait are numerically simulated with a two-dimensional form of hydrodynamic model. It has been known that nonlinear interaction of dominant diurnal constituents K1 and O1 results in new oscillation with the same period of Mf tide. Analysis of computed sea level and currents is aimed primarily at describing the enhanced currents and patterns of energy flow in the Strait. Next, the focus of our model study is investigation of mechanisms of pseudo-fortnightly current enhancement where passage-flow interacts with diurnal current variations, resulting in temporal change in the friction due to “form drag”. Thus, we combine the study for form drag of passage-flow with the hydrodynamic interactions of diurnal tidal currents to provide some insight into the locally generated fortnightly tidal forcing within the Strait.