Kazuo Nadaoka

Publications (3)3.55 Total impact

• Article: Existence of eddies at crossroad of the Indonesian seas

  Aditya R. Kartadikaria, Yasumasa Miyazawa, Kazuo Nadaoka, Atsushi Watanabe
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  ABSTRACT: An eddy-resolving Indo-Pacific ocean circulation model was applied to highlight the behavior of eddies throughout the Indonesian seas. The complexity of the topography and coastline at the entrance of the Makassar Strait induce an eddy-type throughflow, instead of a straightforward flow. A sill and a narrow passage in the Makassar strait creates a barrier and impedes the continuation of eddies from the Pacific ocean, but the existence of a steep deep basin (>500m depth) between the Java and Flores seas indicates a possible area for eddies. Based on our numerical results, we described the presence of a unique eddy structure north of Lombok Island, which we designated the “Lombok Eddy” and verified it by performing a drifter release field experiment and reviewing monthly mean climatology data from the World Ocean Atlas 2001 and XBT PX2 track data. NCEP/NCAR reanalysis, satellite observation data, and mixed layer depth analysis were also used to confirm these processes. By analyzing numerical simulation results and available temperature datasets, two additional eddies were found. All eddies form primarily due to eastward local winds correlated with seasonal monsoon winds during the austral summer. These eddies vary synchronously at an interannual time scale. Together, they are referred to as the Lombok Eddy Train (LET), which affects the surface layer down to a depth of 60m, and the intensity of the eddy system is strongly affected by mixed layer depth variability from December to February. KeywordsLombok eddy train–Wind stress–February–Upwelling-downwelling–Cyclonic-anticyclinic
  Ocean Dynamics 05/2012; 62(1):31-44. · 1.77 Impact Factor
• Article: Numerical study of surface water circulation around Sekisei Lagoon, southwest Japan

  Li-Feng Lu, Yasumasa Miyazawa, Wei Cui, Kazuo Nadaoka
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  ABSTRACT: This paper discusses the variability of surface currents around Sekisei Lagoon using a nested grid ocean circulation model. We developed a triple-nested grid system that consists of a coarse-resolution (1/60° or ∼1.85km) model off Taiwan, an intermediate-resolution (1/300° or ∼370m) model around the Yaeyama Islands, and a fine-resolution (1/900° or ∼123m) model of Sekisei Lagoon. The nested grid system was forced by wind and heat flux calculated from six-hourly atmospheric reanalysis data and integrated over the period from May to July 2003. The coarse-resolution model was driven by lateral boundary conditions calculated from daily ocean reanalysis data to include realistic variation of the Kuroshio and mesoscale eddies with spatial scales of ∼500–700km in the open ocean. The tidal forcing was included in the intermediate-resolution model by interpolating sea level data obtained from a data-assimilative tidal model. The results were then used to drive the fine-resolution model to simulate the surface water circulation around Sekisei lagoon. Model results show that (1) currents inside the lagoon are mainly driven by tide and wind; (2) there exists a strong southwestward current along the bottom slope in the southeast portion of the lagoon; the current is mainly driven by remote mesoscale eddies and at times intensified by the local wind; (3) the flow relaxation scheme is effective in reducing biases along the open boundaries. The simulated currents were used to examine the retention and dispersion of passive particles in the surface layer. Results show that the surface dispersion in the strong open ocean current region is significantly higher than that inside the lagoon. KeywordsNumerical model-Sekisei Lagoon-Yaeyama Islands-Hydrodynamic dispersion
  Ocean Dynamics 04/2012; 60(2):359-375. · 1.77 Impact Factor
• Source

  Available from: terrapub.co.jp

  Article: Marine Ecosystem Simulation in the Indonesian Seas

  Yoshikazu Sasai, Aditya R Kartadikaria, Yasumasa Miyazawa, Kazuo Nadaoka
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  ABSTRACT: An eddy-resolving ocean model incorporating biological processes was applied to the Indonesian Seas to understand the current marine ecosystem and to investigate the influence of river discharges on the marine ecosystem. The model captures surface ocean circulation and relevant energetic eddy activity in the complex topography of the Indonesian archipelago. The simulated surface chlorophyll data reproduced a distribution similar to that of the satellite ocean color data. The model shows high concentrations of surface chlorophyll in the coastal and Indonesian archipelago regions and low concentrations in the subtropical region. The model also shows the large impact of river discharges on the marine ecosystem in the estuary.
  01/2011;