久木　幸治 (ヒサキ　ユキハル)

Hisaki Yukiharu

写真a

科研費研究者番号

60305183

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http://w3.u-ryukyu.ac.jp/yhisaki/index.html

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  • 併任   琉球大学   理学部   物質地球科学科   教授  

  • 併任   琉球大学   理工学研究科   物質地球科学専攻   教授  

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取得学位 【 表示 ／ 非表示 】

  • 東北大学 -  博士（理学）  その他 / その他

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職歴 【 表示 ／ 非表示 】

  • 1998年04月
    　
    　

      - , University of the Ryukyus, Faculty of Science, Department of Physics and Earth Sciences, Meteorology Oceanography Sedimentology, Professor  

  • 1998年04月
    -
    継続中

      琉球大学　理学部　物質地球科学科　海洋水圏科学講座　教授  

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研究キーワード 【 表示 ／ 非表示 】

  • 海洋物理学,海洋リモートセンシング

  • 海洋リモートセンシング

  • 海洋物理学

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  • 自然科学一般 / 大気水圏科学

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主たる研究テーマ 【 表示 ／ 非表示 】

  • 海洋レーダによる波浪観測手法の開発

  • 沖縄近海域の海流の観測とその解析

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論文 【 表示 ／ 非表示 】

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

    Hisaki Y.

    Deep-Sea Research Part I: Oceanographic Research Papers ( Deep-Sea Research Part I: Oceanographic Research Papers )  195   2023年05月 [ 査読有り ]

    掲載種別: 研究論文（学術雑誌）

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      DOI

  • 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 ( Climate )  11 ( 3 )   2023年03月 [ 査読有り ]

    掲載種別: 研究論文（学術雑誌）

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      DOI

  • 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年10月 [ 査読有り ]

    掲載種別: 研究論文（学術雑誌）

    　概要を見る

    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年08月 [ 査読有り ]

    掲載種別: 研究論文（学術雑誌）

    　概要を見る

    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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      DOI

  • Variability of wave height in the Sea of Japan

    Hisaki Y.

    Continental Shelf Research ( Continental Shelf Research )  233   2022年01月 [ 査読有り ]

    掲載種別: 研究論文（学術雑誌）

    　概要を見る

    The Sea of Japan is a semi-enclosed sea located in the northwest Pacific area. There has been no study conducted to examine the relationship between the interannual variability of the wind field and the spatial variability of wave height in the Sea of Japan. We examined the relationship between the spatiotemporal variability of the wave height and the wind field in the Japan Sea using monthly mean ERA5 reanalysis data. Firstly, it is demonstrated that the ERA5 wave height closely matches that of moored buoys. Following that, we investigated the relationship between the wave height and the wind anomaly distribution using empirical orthogonal function (EOF) and self-organizing map (SOM) analysis. This is the first study to examine the spatial variation of wave height using the SOM. The EOF's first mode is a mode that oscillates in the central region of the Sea of Japan, while the second mode is a north-south dipole mode. In each season, the wave height anomaly EOF mode had a significant correlation with a variety of climatic indices. Although the correlation between EOF of wave height anomaly and EOF of wind speed anomaly was not high throughout the year, the correlation between them was high for each season. The SOM revealed a pattern consistent with the EOF analysis's first and second modes. Throughout the year, the relationship between wave height and wind speed anomaly patterns is not strong. The link, however, varies with the seasons. The frequency of patterns with increased wave height anomalies in the central Japan Sea has increased in recent years. This is consistent with the EOF first mode's long-term trend.

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      DOI

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  • 陸上設置型レーダによる沿岸海洋観測

    久木幸治　他 ( 担当: 共著 )

    土木学会海岸工学委員会編  2001年03月 ( 担当ページ: p.50 )

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