Development of an operational coastal model of the Seto Inland Sea, Japan

Abstract

We have developed a coastal model of the Seto Inland Sea, Japan, for a monitoring and forecasting system operated by the Japan Meteorological Agency (JMA). We executed a hindcast experiment using reanalysis datasets for the atmospheric and lateral boundaries without ocean initialization by data assimilation. The seasonal variability is verified to be realistic by comparing sea surface temperature and salinity of the hindcast experiment with observations. With a horizontal resolution of approximately 2 km, the model represents explicitly various coastal phenomena with a scale of 10-100 km, such as the Kuroshio water intrusion into Japanese coasts. This leads to good representation of intramonthly variations. For example, intensity of the sea level undulations with a period shorter than 23 days shows 1.6-fold improvement, as compared to the present model of JMA with the horizontal resolution of approximately 10 km. In addition to the increased resolution, the model is optimized for coastal modeling as follows. Incorporation of a tidal mixing parameterization reduces a high temperature bias in the Bungo Channel (a western channel of the Seto Inland Sea) and contributes to formation of a frontal structure. An accurate dataset of the river discharges is used for runoff, which has a strong impact on salinity. Enhancement of coastal friction improves surface currents. Owing to the increased resolution and these optimizations, the model shows realistic variability in a wide temporal range from several days to seasons. Root-mean-square errors of sea surface temperature and heights are evaluated as 1-2 K and 7-10 cm, respectively, without data assimilation. In the eastern part, however, the predictability is relatively low, which might be related to representation of an eastward mean flow in the Seto Inland Sea.

Tidal control of the flow through long, narrow straits: a modeling study for the Seto Inland Sea

“…Therefore, an eastward volume transport is expected if the SSH difference between the channels drives the throughflow, which is opposite to the observational estimate 2 . The throughflow direction in previous numerical simulations 7,8 using ocean general circulation models (OGCMs) with realistic settings is also eastward, consistent with the SSH difference between the channels during the corresponding periods.…”

“…Because the sporadic intrusion of Kuroshio water in the Bungo Channel is pointed out to be blocked during spring tides due to tidal mixing and tidal residual eddies 9,10 , it is expected that tides may similarly suppress the throughflow. Taking this into account, a recent numerical simulation 8 used enhanced horizontal viscosity near the coast for better representation of currents by suppressing the throughflow. It should also be noted that an assumption used by the observational study 2 , that time-averaged currents are parallel to the tidal currents, is not appropriate in the presence of tidal residual eddies.…”

Development of high-resolution future ocean regional projection datasets for coastal applications in Japan

“…Table 1 presents the detailed configurations of each model. The bathymetry of the JPN02 model was based on the JTO-PO30v2 data provided by the Marine Information Research Center, and several detailed settings (e.g., physical schemes and parameters) of the JPN02 model were similar to those described by Sakamoto et al (2016).…”

Unusually high sea level at the south coast of Japan in September 2011 induced by the Kuroshio

“…The horizontal resolution is about 2 km (1/33 • × 1/50 • ). There are 50 vertical levels with the layer thickness increasing from 4 m to 600 m. More detailed descriptions on the Seto model are given in Sakamoto et al (2016).…”