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Published Papers 【 display / non-display 】

• Swell and wind-wave height variability in the East China Sea

  Yukiharu Hisaki

  Ocean Dynamics ( Springer Science and Business Media LLC )  73 ( 8 ) 493 - 515   2023.08 [ Peer Review Accepted ]

  Type of publication: Research paper (scientific journal)

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• Use of drifting buoys for wave observation: Effect of current on wave data

  Yukiharu Hisaki

  Deep Sea Research Part I: Oceanographic Research Papers ( Elsevier BV )  195   103986 - 103986   2023.05 [ Peer Review Accepted ]

  Type of publication: Research paper (scientific journal)

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• Sea Level Variability in the Equatorial Malacca Strait: The Influence of Climatic–Oceanographic Factors and Its Implications for Tidal Properties in the Estuarine Zone

  Ulung J. Wisha, Yusuf J. Wijaya, Yukiharu Hisaki

  Climate ( MDPI AG )  11 ( 3 ) 70 - 70   2023.03 [ Peer Review Accepted ]

  Type of publication: Research paper (scientific journal)

  　View Summary

  The sea level trend in the equatorial Malacca Strait is a significant issue that needs to be reviewed since it is an area of interest. Assessing its future impact on estuarine tidal characteristics is worth studying because it relates to the potency of coastal damages. This study aimed to discuss the relationship between sea level variations and anomalies and their possible triggering factors and to estimate the future impacts on the tidal properties in the estuarine zone. Tide gauge and altimetry data in the Tanjong Pagar site were used to assess the sea level trends over 27 years of observation (from 1992 to 2019). Both altimetry and tide gauge data showed an upward trend, with 0.24 cm/year and 0.39 cm/year, respectively. Due to the near-equatorial area of interest, sea level variability is more synchronized with ENSO rather than IOD. At some points, ENSO shapes the sea level fluctuation, with an R2 of less than 10%. For specific periods, the coupling effects between MJO and La Niña may trigger higher evaporation in the maritime continent, triggering increasing sea levels. Of particular concern, among the other assessed factors, the zonal currents and winds (wind-driven currents) are strongly correlated with sea level variations, primarily during the NE monsoon and the second transitional periods, with a determination coefficient of about 18–36%. As a result of sea level rises, it is estimated that tidal constituent amplitudes will increase by about 8.9% and 18.3% in 2050 and 2100, respectively. The increase in tidal range will possibly relate to the tidal bore passage in the Kampar estuary. Therefore, more advanced hydrodynamic modeling is necessary to determine the impact of sea level rises on tidal bore generation.

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• The Western Pacific North Equatorial Countercurrent Responses to Two Forms of El Niño during the Period 1978 to 2017

  Yusuf Jati Wijaya, Ulung Jantama Wisha, Yukiharu Hisaki

  Climate ( Climate )  10 ( 10 )   2022.10 [ Peer Review Accepted ]

  Type of publication: Research paper (scientific journal)

  　View Summary

  This research aims to examine how the Western Pacific North equatorial countercurrent (NECC) flow reacts to two different forms of El Nino (EN) over a 40-year period. To establish the prevailing modes for each season, we implemented Empirical Orthogonal Function (EOF) analysis on the eastward current component of the Ocean Reanalysis System 5 (ORAS5) dataset. In comparison to the Central Pacific (CP) episode, the time series principal component of the first mode (PC1) demonstrated that the strongest NECC's magnitude often emerged during the development period (spring to fall) of the Eastern Pacific (EP) EN event. However, in episode CP 2002/2003, we witnessed an abnormal behavior in which the stronger NECC manifested. This was due to the emergence of a strong anomalous westerly wind, which differed from other CP events and forced the NECC's magnitude to be greater. When approaching the peak stage, on the other hand, the magnitude of the NECC during the CP episode was typically greater than that of the EP episode. The NECC's magnitude fell greatly in the second year of the EP episode, particularly during the spring season, since most EP episodes would transition into an La Nina (LN) event in the succeeding event. During the EP EN, it was found that the strength of the westerly wind had a bigger effect on the NECC than during the CP EN.

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• Real-Time Properties of Hydraulic Jump off a Tidal Bore, Its Generation and Transport Mechanisms: A Case Study of the Kampar River Estuary, Indonesia

  Ulung Jantama Wisha, Yusuf Jati Wijaya, Yukiharu Hisaki

  Water (Switzerland) ( Water (Switzerland) )  14 ( 16 )   2022.08 [ Peer Review Accepted ]

  Type of publication: Research paper (scientific journal)

  　View Summary

  Since the hydraulic jump off a tidal bore in the Kampar Estuary has never been well-described, real-time measurements of hydraulic jump properties are crucial to understanding the tidal bore characteristics. This study aims to determine the real-time properties of a tidal bore generation, hydraulic jump, and transport mechanism in the Kampar River estuary. Tidal harmonic and range are analyzed using least-square-based tidal modeling. The tidal bore height and turbulent velocity records based on ADCP surveys in the estuary and upstream area are used to determine the hydraulic jump properties. Furthermore, an acoustic-based approach is also employed to quantify the suspended sediment concentration and flux during the passage of the bore. Kampar Estuary is predominated by semidiurnal co-tidal components (M2 and S2), where, based on the phase lag magnitude, it is categorized as an ebb-dominant estuary. This finding is proven by the more intense and prolonged ebb phases, especially during spring tidal conditions where the tidal range reaches 4 m. Of particular concern, the tidal bore height declines by 1.5 m every 20 km upstream with an erratic turbulent velocity. A sudden increase in transverse and vertical velocity during the passage of bore (ranging from -0.9 to 0.2 m/s) reflects the potency of sediment resuspension in the surrounding river edge marked by the significant increase in suspended sediment flux of about 3.7 times larger than at the end of the ebb tide. However, long-term measurement and regular bathymetry surveys are crucial to monitor the tidal bore behavior and morpho-dynamics in the Kampar River estuary.

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Other Papers 【 display / non-display 】

Other Papers 【 display / non-display 】

• 海洋レーダによる海上風補正と沿岸波浪推算

  久木幸治

  日本海洋学会大会講演要旨集   2017   52   2017.09

   

  J-GLOBAL

• 複数の停滞及び伝搬する擾乱における時間補間とモデルへの影響

  久木幸治

  日本海洋学会大会講演要旨集   2016   151   2016.08

   

  J-GLOBAL

• 単一及び複数の海洋レーダによる推定波浪スペクトルの比較

  久木幸治

  日本海洋学会大会講演要旨集   2015   90   2015.09

   

  J-GLOBAL

• Development of HF ocean radar in Japan.

  Hisaki. Y.

  Proceedings of the international conference on radar, IEEE. ( その他の出版社 )    510 - 514   2003.03

   

Grant-in-Aid for Scientific Research 【 display / non-display 】

Grant-in-Aid for Scientific Research 【 display / non-display 】

• Grant-in-Aid for Scientific Research(C)

  Project Year: 2020.04  -  2024.03 

  Direct: 3,300,000 (YEN)  Overheads: 4,290,000 (YEN)  Total: 990,000 (YEN)

• Grant-in-Aid for Scientific Research(C)

  Project Year: 2020.04  -  2024.03 

  Direct: 3,300,000 (YEN)  Overheads: 4,290,000 (YEN)  Total: 990,000 (YEN)

• Grant-in-Aid for Scientific Research(C)

  Project Year: 2020.04  -  2024.03 

  Direct: 3,300,000 (YEN)  Overheads: 4,290,000 (YEN)  Total: 990,000 (YEN)

• Study on estimation of wave spectra by HF radar and wave hindcast

  Grant-in-Aid for Scientific Research(C)

  Project Year: 2014.04  -  2019.03 

  Investigator(s): HISAKI Yukiharu 

  Direct: 3,900,000 (YEN)  Overheads: 5,070,000 (YEN)  Total: 1,170,000 (YEN)

  　View Summary

  It is possible to observe surface ocean currents and waves by high-frequency ocean radars. However, the wave estimation method has been established. The reporter estimated ocean wave spectra by the single radar. The estimated wave parameters were compared with in-situ observations and model predicted wave parameters. Next, the method was developed by estimating wave spectra on the orthogonal coordinate grid points. This method can be applied to both single and multiple radars. In addition, the time interpolation of the sea surface wind was improved in order to improve the accuracy of wave prediction.

• Study on estimation of wave spectra by HF radar and wave hindcast

  Grant-in-Aid for Scientific Research(C)

  Project Year: 2014.04  -  2019.03 

  Investigator(s): HISAKI Yukiharu 

  Direct: 3,900,000 (YEN)  Overheads: 5,070,000 (YEN)  Total: 1,170,000 (YEN)

  　View Summary

  It is possible to observe surface ocean currents and waves by high-frequency ocean radars. However, the wave estimation method has been established. The reporter estimated ocean wave spectra by the single radar. The estimated wave parameters were compared with in-situ observations and model predicted wave parameters. Next, the method was developed by estimating wave spectra on the orthogonal coordinate grid points. This method can be applied to both single and multiple radars. In addition, the time interpolation of the sea surface wind was improved in order to improve the accuracy of wave prediction.

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