Reveal of Dynamics of Barotropic Exchange between the Sea of Okhotsk and North Pacific through Tidal Forcing in High-Resolution Ocean General Circulation Model: the Modification of the Western Boundary Current Pathway by Tidal Rectification

Hung Wei Shu, Hokkaido University, Pan-Okhotsk Research Center, Institute of Low-Temperature Sciecne, Sapporo, Japan, Humio Mitsudera, Institute of Low Temperature Science, Hokkaido University, Sapporo, Japan, Kaihe Yamazaki, National Institute of Polar Research, Tokyo, Japan, Takao Kawasaki, Atmosphere and Ocean Research Institute, the University of Tokyo, Kashiwa, Chiba, Japan, Hideharu Sasaki, JAMSTEC, Yokohama, Japan, Tomohiro Nakamura, Hokkaido Univ, Sapporo, Japan and Hatsumi Nishikawa, Hokkaido University, Sapporo, Japan
The volume transport between the Sea of Okhotsk and North Pacific is determined by the pathway of the western boundary current, East Kamchatka Current. When East Kamchatka Current approaches the middle island chain, since the friction on the east side of middle island chain is enhanced, the barotropic transport should generate though Northern-end and Southern-end of middle island chain for balancing the circular integrated momentum equation.

By increasing the resolution of topography in OGCM COCO model, the volume transport between the Sea of Okhotsk and North Pacific decreases and is far from observation data suggestion, except adding the tidal component in the model momentum equation. The discrepancy between Non-Tidal and Tidal run implies that tidal induced vertical diffusivity enhancement and tidal topographic trapped wave are both possibly dominating in Okhotsk-Pacific exchange system by shifting the direction of East Kamchatka Current. We thus manipulate two experiments to clarify each function: 1. Compiling tidal vertical diffusivity value into Non-Tidal run to test the effect of releasing topography constraints by tidal vertical mixing on western boundary current, and 2. Inserting the tidal component into Non-Tidal run to observe the transition of flow pattern.

Finally, we present the mechanism of Okhotsk-Pacific exchange system as a multi-compound dynamics system in high-resolution OGCM within tidal forcing. Positive relative vorticity injection via tidal topographic trapped waves located at the north-east side of middle island chain enforces East Kamchatka Current containing higher potential vorticity value. The East Kamchatka Current thus shift the direction to coastal side (shallower water column height) for its potential vorticity conservation and increases the volume transport between two basin through the enhancement of friction on the east side of middle island chain(See Figure). Meanwhile, the tidal vertical diffusivity value decreases the transportation volume via reducing the kinetic energy caused by strong vertical mixing along the bathymetry.