Development of a 2-km resolution ocean model covering the coastal seas around Japan for operational application

In order to expand the coastal ocean monitoring and forecasting system of the Japan Meteorological Agency from the Seto Inland Sea to the entire coastal seas of Japan, a 2-km resolution model has been newly developed. We investigated the model performance based on a 4-year hindcast experiment without data assimilation. The model realistically reproduced basic distributions and seasonal variations of sea surface temperature, salinity, sea level, etc. Small-scale features in the coastal seas, such as fronts, were also well simulated due to the high resolution. Daily sea level variations on the coasts followed the tide gauge observation with an error of 7.1 cm on average. Transports through main Japanese straits were also consistent with previous research. In addition to expanding the domain, some dynamical elements are newly introduced. One of the major updates is implementing of explicit tides with high precision, as the amplitude error was only 9.2% and the phase error was 10.2 ∘ for the M2 tide. The second is coupling of a sea ice model reproducing the seasonal development of sea ice in the Sea of Okhotsk. The third is introduction of approximately 4000 river inflows across Japan to improve salinity in coastal seas. Introduction of the inverse barometer effect and high-resolution atmospheric forcings also contributed to coastal sea level variations. The Japan Meteorological Agency plans to widely utilize the model with a new data assimilation system for coastal disaster prevention and oceanic condition monitoring, and our verification results support the utility of the model.