Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

Satellite altimeter data assimilation into a regional ocean model southwest of Japan is studied based on an approximate Kalman filter. System error or process noise has been conventionally attributed to surface meteorological conditions. However, the effects of surface meteorological change by the data assimilation decay rapidly to depths and may not propagate into deep layers. Here, we attempted to employ lateral boundary update by the data assimilation in comparison with surface forcing control to improve the representation of the Kuroshio Current. The magnitude of process noise from the surface and lateral boundary forcings was separately determined by minimizing the root-mean-square difference of temperature. The results showed that the effect of lateral forcing propagated into deep layers, and it performed better than the experiments controlling surface conditions around the Kuroshio Current where the water depth is deep. However, the data assimilation of surface meteorological condition was found to be still effective in shallow area. The cross-spectral analysis indicated that satellite altimeter data assimilation can improve the representation of long-term Kuroshio Current variability.

DOI： 10.1007/s10872-021-00629-y

Web of Science

Scopus

Language：English   Publishing type：Research paper (scientific journal)  

The features of coastal upwelling in the southwestern Yellow Sea were investigated based on oceanology data from a research cruise and a regional circulation model. The observation data suggest that a relatively colder and saltier water core exists from the deeper layer to the surface, off the Subei Bank. The concentrations of nutrients also suggest that coastal upwelling is beneficial for nutrient enrichment in the upper layer. The numerical simulations are in good agreement with oceanology observations. Furthermore, sensitivity experiments indicate that, in addition to the tidal-induced upwelling and tidal mixing proposed in previous studies, the summer monsoon is also critical to vertical circulation in the southwestern Yellow Sea. The southwesterly wind stress and positive wind stress curl make considerable contributions to upwelling off the Subei coast compared with tidal motions. Moreover, this study also proposes that changes in the summer monsoon and its curl may have been helpful to the formation of upwelling during the past decade, which may have provided a favorable marine environment for the frequent occurrence of green tides. This study provides a theoretical basis for the mechanisms of coastal upwelling and the nitrogen cycle in the Yellow Sea.

DOI： 10.3390/jmse9091021

Language：English  

This study clarifies the necessity of an extraordinary large coefficient of vertical viscosity for dynamical ocean modeling in a shallow and narrow strait with complex bathymetry. Sensitivity experiments and objective analyses imply that background momentum viscosity is on the order of 100 cm2 s−1, while tracer diffusivity estimates are on the order of 0.1 cm2 s−1. The physical interpretation of these estimates is also discussed in the last part of this paper. To obtain reliable solutions, this study introduces cyclic application of the dynamical response to each parameter to minimize the number of long-term sensitivity experiments. The recycling Green’s function method yields weaker bottom friction and enhanced latent heat flux simultaneously with the increased viscosity in high-resolution modeling of the Tsushima/Korea Strait.

DOI： 10.1175/jtech-d-20-0156.1

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

As a marine renewable resource, ocean thermal energy conversion (OTEC) is gaining attention because of its sustainability and environment-friendly characteristics. The thermal energy potential in the open ocean has been well documented in the previous literature. However, regional potential near the coast is not easily estimated using methods and parameters for global estimation. This study estimates the thermal energy potential of the Aguni Basin in the East China Sea using a high-resolution ocean model. An additional simulation without tide is performed to clarify the tidal effect. The results show that two traditional methods overestimate the OTEC power density in the Aguni Basin, while two other approaches are able to improve the estimation. The OTEC power density in the Aguni Basin is much larger than that in the global ocean, largely owing to vigorous tidal mixing. Strong and sustainable power generation is possible near the northeastern slope of Kumejima Island as a result of the high OTEC power density within a short distance to the coast.

DOI： 10.1016/j.apor.2020.102185

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

Ocean current power near the Japanese coast was estimated using a high-resolution, three-dimensional ocean model. Two experiments were conducted to distinguish the impact of the Kuroshio large meander. The simulation results were validated by comparison with measurements. To choose the proper site for ocean current power generation experiment, we quantitatively analyzed the variation of the current field for three candidate areas: around the Tokara Strait, south of Cape Ashizuri (AS), and south of Cape Shionomisaki (SH). The results show that the current around the Tokara Strait is the weakest among the three candidates. The current south of SH is strongest for the non-large-meander period. The area south of AS is promising for ocean current power generation, because the current is stable and strong regardless of the large meander, and the average ocean current power density can reach 1 kW/m2.

DOI： 10.1007/s40722-017-0103-9

Event date： 2026.5

Language：English   Presentation type：Oral presentation (general)  

Venue：Chiba City, Chiba Prefecture   Country：Japan  

Event date： 2026.3

Language：English   Presentation type：Oral presentation (general)  

Venue：Gwangju City, South Korea   Country：Korea, Republic of  

Event date： 2025.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Okinawa, Japan   Country：Japan  

Event date： 2025.7

Language：English   Presentation type：Oral presentation (general)  

Venue：Busan City, South Korea   Country：Korea, Republic of  

Event date： 2025.3

Language：English   Presentation type：Oral presentation (general)  

Venue：Nagasaki City, Nagasaki Prefecture   Country：Japan  

Work type：Database science  

researchmap

Work type：Web Service   Location：Kagoshima University  

This real-time ocean forecasting system adopts the DREAMS_Ep model (Liu and Hirose, 2022). It is a 3-dimensional primitive equation model based on the Research Institute for Applied Mechanics Ocean Model (RIAMOM) originally developed by Lee et al. (2003). Its horizontal resolution is 1/60° × 1/75° corresponding to about 1.5 km, and it has 114 levels in the vertical direction. The model covers a rectangle region of 126–132.65°E and 26–33.24°N. The topography is derived from JTOPO30 dataset provided by the Marine Information Research Center of the Japan Hydrographic Association (http://www.mirc.jha.jp). The open boundary conditions are from the output of DREAMS_M model (Hirose et al., 2013). The meteorological forcing data are GSM and MSM data provided by Japan Meteorological Agency. Satellite altimeter observations obtained from the AVISO website (https://aviso.altimetry.fr), HIMAWARI SST observations provided by JAXA website (https://earth.jaxa.jp/en/), and Smart-ACT CTD (Takikawa et al., 2019) and ADCP measurments by fishermen are assimilated using an approximate Kalman filter based on Fukumori and Malanotte-Rizzoli (1995) to improve the accuracy of the forecasting system. The 10-day forecasting is updated everyday at 09:00 JST (00:00 UTC).

Other Link： https://drep2.oce.kagoshima-u.ac.jp/