Numerical experiment for a westward tail of the Tsugaru Gyre along the Hidaka shelf slope

Kobayashi Naoto, Isoda Yutaka, Asahi Keijiro

doi:10.5928/kaiyou.24.5_171

<p>A recent hydrographic survey indicated that a local bifurcation of the Tsugaru Gyre, which appeared over the Hidaka shelf slope in early summer, accompanied a clockwise, small eddy. To examine the bifurcationʼs formation and development processes, we performed a numerical experiment using an f-plane σ-coordinate model with idealized shelf topography. During the stage at which the Tsugaru Gyre grew and intruded into the northern shelf slope area, the lower-layer water column on the slope was continuously contracted to induce a negative relative vorticity. As a consequence, the nearly barotropic or bottom-trapped motion with clockwise rotation emanated west of the intrusion area and then propagated westward along the slope. This motion was associated with two types of low-frequency waves characterized by surface and bottom intensifications. On the contrary, an anti-clockwise eddy formed east of the intrusion area and stably fed on the offshore bottom cold water into the coastal area. These processes suppressed the eastward shift of the Tsugaru Gyre by the mirror effect of the lateral boundary. Thus, the above-mentioned small eddies were found to dominate the Tsugaru Gyre, shifting westward along the Hidaka shelf slope.</p>

Numerical experiment for a westward tail of the Tsugaru Gyre along the Hidaka shelf slope

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