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

Abstract

Even in coastal oceans where tidal currents are predominant, long-term mean currents are of great interest since they are responsible for the transport of materials over long timescales. Tides could significantly affect mean currents in long, narrow straits due to tide-topography interaction, but it is yet unclear how and to what extent tides control throughflows. Here, we focus on the throughflow in the Seto Inland Sea, Japan, which has enormous impacts on the marine environment while its long-term mean characteristics, even the flow direction, are not well described by observations. By using a state-of-the-art ocean model, we show that the simulated throughflow is eastward on annual average and its volume transport is considerably suppressed by tides. It is found that tides enhance mixing and induce time-mean eddies, and both work to reduce the throughflow. A westward throughflow was previously estimated based on an acoustic measurement. The discrepancy between this estimate and our result would be due to whether or not such eddies are taken into account. These findings imply that tides may also suppress the throughflow of the other straits around the world. Revealing such tidal effects may contribute to a better performance of oceanic and climate simulations.

Abnormal surges and the effects of the Seto Inland Sea circulation in Hiroshima Bay, Japan

“…The correction process is described in Section 3.3. This result also depicted a spatial distribution of sea level similar to that described in the literature (Kurogi and Hasumi, 2019;Nakatani et al, 2020). The 61-day-averaged surface elevation (black solid line in Figure 4) exhibited an analogous west-high-east-low pattern, a basic structure in the spatial distribution of sea surface elevation.…”

“…The sea level distribution of the SIS has distinct characteristics. Basically, the sea level in the Bungo Channel is higher than that in the Kii Channel (west high-east low), inducing easterly throughflow in the SIS (Kurogi and Hasumi, 2019;Nakatani et al, 2020). Nakatani et al (2020) suggested that the throughflow via the sea level gradient is related to the Kuroshio current.…”

“…Nakatani et al (2020) suggested that the throughflow via the sea level gradient is related to the Kuroshio current. Kurogi and Hasumi (2019) calculated the volume transport of seawater across the SIS. They found that considering tidal effects, such as vertical diffusivity and viscosity and the generation of tidal residual eddies, was important for calculating transport precisely.…”

Simulated distributions of pumice rafts in Japan following eruptions at volcanic islands and submarine volcanoes

“…For more reliable future simulations, we plan to downscale the model resolution from 10 to 2 km and consider tidal mixing and direct wind effects, which are known to affect ocean currents and pumice drift paths. Kurogi and Hasumi (2019) showed that near-coast ow elds are strongly affected by tidal mixing. Wind affects pumice drift paths in two ways: indirectly by driving sea surface currents and directly by dragging the pumice itself.…”

Unstructured Grid-Based River–Coastal Ocean Circulation Modeling towards a Digital Twin of the Seto Inland Sea

“…Through narrow and complex straits, tidal waves flowing in from these channels converge near Hiuchi Nada and Bisan Seto in the central part of the SIS. This results in difficulties in reproducing tides in the SIS [20], and although tides were reproduced in a previous study, a quite large root-mean square error (RMSE) of 40 cm was calculated in the inner part of the SIS [21]. Understanding the spatial distributions of currents in these areas is critical for environmental impact assessments, ocean energy resource assessments, marine safety, navigation, sedimentation, aquaculture, and other factors.…”