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We examine inter-annual and inter-seasonal effects of the fluctuating Kuroshio path, sea-surface wind and tides on circulation and larval dispersal in the Seto Inland Sea (SIS) using a massive amount of Lagrangian particles released in the modeled SIS circulation field with a double-nested, high-resolution ROMS-based SIS model for the years 2007-20...
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Results of long-term studies of zooplankton species in the Amur Bay (Japan Sea) are analyzed. Two seasonal «waves» of the allochtonous species are defined: the first in the early summer that is formed mainly by inter-zonal copepods spawning in the deep layers ( Metridia pacifica , Neocalanus plumchrus, Calanus glacialis ) and the second in the late...
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... The results of the Seto-2km model are compared with those of another higher-resolution SIS model developed in Kosako et al. (2016) (hereinafter Seto-600m; Fig. 3 and Table 1). The Seto-600m model is in a double-nested configuration based on ROMS with grid spacings of 2 km and 600 m, embedded in the JCOPE2 reanalysis. ...
... The freshwater discharges from all the major rivers in each model domain are given as monthly climatological freshwater mass point sources based on the Annual Record of Rainfall and Discharge Database issued by the Japan River Association. The Seto-600m model was also carefully validated with observed surface temperature and salinity in Kosako et al. (2016) as well as high-frequency tidal signals in the SIS in Uchiyama et al. (2018b). Other numerical configurations are the same as those of the Seto-2km model, as summarized in Table 1. ...
The primary objective of this study is to develop a new weather routing system for vessel navigation in coastal and marginal seas based on the A-star algorithm. The cost function inherent in the original A-star algorithm is modified to account for oceanic and atmospheric conditions around the vessel of interest. Three options are introduced to search for optimal paths with the shortest travel distance, shortest travel time, and minimal fuel consumption. An avoidance algorithm for unsafe conditions is further incorporated to exempt any arbitrary area from the navigation solution. Furthermore, a compact ocean circulation model based on the Regional Ocean Modeling System executable on typical laptop PCs is configured for a vessel-borne weather routing system; the system is successfully applied to evaluate the optimal vessel paths in the Seto Inland Sea, where high-frequency tidal currents modified by complex topography make it essential to alter the vessel's speed.
... Another important factor that should be considered in STEAMER is tide, which MOVE and RTOFS-Global do not consider. Kosako et al. (2016) [8] conducted Lagrangian particle tracking in the Seto Inland Sea, where the Ikata nuclear power plant is located. Their sensitivity experiments focusing on tidal influences demonstrated that material transport toward the offshore direction was largely suppressed by vertical mixing due to tides; thus, the usage of nontidal MOVE and RTOFS-Global as input data for STEAMER may lead to overestimation of offshore material transport in tidal-flow-dominated waters. ...
... Another important factor that should be considered in STEAMER is tide, which MOVE and RTOFS-Global do not consider. Kosako et al. (2016) [8] conducted Lagrangian particle tracking in the Seto Inland Sea, where the Ikata nuclear power plant is located. Their sensitivity experiments focusing on tidal influences demonstrated that material transport toward the offshore direction was largely suppressed by vertical mixing due to tides; thus, the usage of nontidal MOVE and RTOFS-Global as input data for STEAMER may lead to overestimation of offshore material transport in tidal-flow-dominated waters. ...
... The reason for the difference in 137 Cs distribution between the models with and without tidal forcing is that enhanced vertical mixing by tides retards the 137 Cs dilution. These retardations of offshore material transport and dilution due to the coastal flows, small eddies, and tides are consistent with the findings of previous studies [7,8,14]. Figure 9 shows the area-averaged surface K e , depth-averaged vertical velocity variance, and depthintegrated 137 Cs concentration variance averaged over the area displayed in Figures 4-8 The submesoscale and tidal effects on the material mixing can be estimated from the area averaged 137 Cs concentration variance from MOVE-WNP (SG-M) and ROMS-L2 (SG-L2 (w/tide)) because the values in Figure 9 are ratios of the corresponding quantities computed with ROMS-L2 (w/o tide) and SG-L2 (w/o tide) models. Thus, the submesoscale effects strengthen the material mixing of concentration by as much as 10 times, while the tidal effects increase material mixing by approximately 3%. ...
Oceanic regional downscaling capability was implemented into Short-Term Emergency Assessment system of Marine Environmental Radioactivity (STEAMER) developed by Japan Atomic Energy Agency to enable us to predict more realistically the oceanic dispersion of radionuclides at higher spatiotemporal resolutions for broader applications. The system consisted of a double-nested oceanic downscaling circulation model with tidal forcing and an oceanic radionuclide dispersion model. This system was used to comparatively examine downscaling and tidal effects on the dispersion of radionuclides hypothetically released from the Fukushima Daiichi Nuclear Power Plant in the colder season. The simulated dissolved ¹³⁷Cs distribution was different from that obtained using coarser-resolution models because downscaling enhanced both horizontal and vertical mixing. The suppression of horizontal mixing and the promotion of vertical mixing by tidal forcing synergistically reduced offshore ¹³⁷Cs transport. In addition, the submesoscale effects strengthened the three-dimensional ¹³⁷Cs fluctuations by <10 times, while the tidal effects promoted slightly increased the intensity of three-dimensional ¹³⁷Cs fluctuations by approximately 3%. This indicated that the submesoscale effects substantially surpassed tidal forcing in oceanic mixing in the coastal margin off Fukushima in the colder season.
... It has unique geographical characteristics and consists of seven main subbasins interconnected by narrow straits and > 3000 islands, which form a complex "basin-strait" system. The SIS is a partially stratified tidal estuary that is concurrently affected by: 1) energetic tidal currents up to 3 ms −1 near straits under dominant semidiurnal, mesotidal conditions with a maximum tidal range of ± 1.2 m; 2) seasonally varying freshwater discharge from 28 major rivers; and 3) quasi-persistent eastward residual circulation (the SIS throughflow) primarily driven by the eastward drifting Kuroshio offshore of the two openings that connect the SIS with the Pacific (e.g., Kosako et al., 2016). The Kuroshio is known to have a considerable impact on the SIS circulation due to sporadic intrusions (Takeoka et al., 1993;Tada et al., 2017) and meandering of the Kuroshio path (e.g., Kawabe, 1987Kawabe, , 1995. ...
... The newly developed L3 and L4 models were validated with observed data. The parent L1 and L2 models agree well with in situ measurements of temperature, salinity, and tides for the 9-year period from 2006 to 2015 in Kosako et al. (2016). Fig. 2 shows scatter plots of the modeled and measured sea surface temperature (SST) and salinity (SSS). ...
... 2a and 3), whereas it is moderate for SSS with a correlation coefficient of 0.379 (Fig. 2b). Such an overall reasonable reproducibility is inherited from their parent models (Kosako et al., 2016). The modeled SSS is overestimated because our model merely accounts for the monthly climatology of the major rivers (Section 2.1) that results in the underestimation of freshwater input to the SIS. ...
Oceanic forcing on offshore oil platforms deployed ubiquitously in the South China Sea (SCS) was evaluated from the medium-term reanalyses based on the in-house regional HYCOM-ROMS oceanic model and the JMA’s GPV-GSM global atmospheric analysis. An extreme value statistical analysis was conducted for determining the maximum surface currents and winds that may occur with multi-decadal exceedance probability. Wind stresses were most energetic off the eastern shore of the Malay Peninsula due to southwestward winter monsoons, while surface currents were intensified off the northern shore of Borneo Island. We assessed the mechanism behind the latter using a volume flux analysis at several cross-sections around the SCS. It was demonstrated that the remote forcing associated with the Kuroshio and Mindanao Currents triggered changes in the fluxes at the Luzon and Celebes Straits that are indirectly but pronouncedly influential to the coastal currents near the Borneo Strait.
A downscaling ocean model for the Southern China Sea (SCS) was developed based on ROMS initialized and forced by the HYCOM+NCODA assimilative global analysis. A multi-year reanalysis was carried out by properly accounting for wind stress and heat budget at surface, freshwater influences from the atmosphere and major rivers, and tidal variability. We successfully reproduced primary dynamics of the SCS in many aspects such as the transient Kuroshio path in the south of Taiwan prominently affecting the circulation of the northern SCS through the Luzon Strait. The Kuroshio and Mindanao Currents originated from the North Equatorial Current concurrently affect the volume fluxes at the Luzon and Celebes Straits, leading to sporadic and systematic intrusion into and discharge out of the SCS. The volume flux budget analysis revealed that these fluxes promote the through flow in the SCS, and consequently influence the formation of the SCS water.
Kinematics, dynamics, and statistical nature of mesoscale oceanic eddies and their effects on the Kuroshio are investigated using a velocity-based automated eddy detection and tracking algorithm proposed by Nencioli et al. (2010) to apply to a 20-year long satellite altimetry dataset provided by AVISO for the entire North Pacific (NP) basin. In the NP, barotropic instability associated primarily with topographic shear and frontal baroclinic instability concurrently promote generation of mesoscale eddies. The eddy sizes and magnitudes of relative and absolute vorticity are inversely correlated, which is well explained by inertial instability and potential vorticity conservation, in particular in the Kuroshio Extension region (KE) and Subtropical Zonal Band (SZB), where eddy kinetic energy is highest in the NP. Mesoscale eddies generally propagate westward as non-dispersive, first-mode baroclinic Rossby waves in the SZB and U.S. West Coast, according to a frequenc-ywavenumber spectral analysis. In contrast, the eddies in the KE are rather multi-directional with notable eastward propagation due to eastward eddy shedding from the eastward-drifting Kuroshio. Furthermore, we show two selected examples, in which mesoscale eddies collided with the Kuroshio to provoke and suppress meander of its path off the continental shelf off Japan.
