Application of MOM6 for Regional and Coastal scale Coupled with the Biogeochemistry Model (COBALTv3)

We have advanced the high-resolution (1/24˚) regional ocean model for Northwest Pacific (KOOS-OPEM), developed by the Korea Institute of Ocean Science and Technology (KIOST) by updating its base model from MOM5 to MOM6. Using this updated model, we conducted sensitivity experiments to compare the performance of simulations under two different vertical coordinate systems: the hybrid z*-isopycnal and the z* coordinate. The results indicated that both coordinate systems successfully reproduced the Kuroshio separation point in close agreement with observation data. In addition, the hybrid coordinate configuration demonstrated a more realistic representation of the Northwest Pacific intermediate water compared to the z* coordinate configuration. However, the hybrid coordinate configuration exhibited a warm bias approximately 1°C greater than that of the z* system in the Kuroshio Current and the East/Japan Sea. To address this issue, we adjusted the maximum thickness of the isopycnal layers, which effectively mitigated the warm biases in these regions. Additionally, this study introduces the regional implementation of MOM6 for the Northwest Pacific coupled with the biogeochemistry model (OPEM-MOM6-COBALT). To address the limitations of the coarse initial conditions for the biogeochemical tracers, a 10-year spinup simulation was conducted to generate improved initial conditions for the biogeochemical tracers. This study evaluated the initial conditions, intended for use in hindcast simulations, against satellite and observational data. Furthermore, we constructed the coastal implementation of MOM6 for the Yeosu-Gwangyang Bay, which will be coupled with the biogeochemistry model using the initial and boundary condition generated from OPEM-MOM6-COBALT simulation. We plan to perform hindcast simulations with these physical-biogeochemical models and compare their performance against observation data.