Sato Tomoya

Understanding Ocean Characteristics in the Waters Around Sado Island Using Autonomous Ocean Observation Devices

Inukai Naoyuki

Currently, offshore wind power generation in Japan is viewed as a key solution for establishing renewable energy as a primary power source.
Furthermore, in the vicinity of Niigata Prefecture, the waters off Murakami City and Tainai City have been designated as a wind power promotion zone under the Renewable Energy Marine Area Utilization Act, and projects to install bottom-fixed wind turbines are underway. Offshore winds in Niigata Prefecture predominantly feature annual average wind speeds of 6–8 m/s across most areas, suggesting that favorable conditions for offshore wind power generation likely exist beyond the waters off Murakami City and Tainai City.
Therefore, this study focuses on the waters off Sado Island in Niigata Prefecture, considered one such promising area for offshore wind power generation, aiming to comprehensively understand its meteorological and oceanographic characteristics. The waters off Sado Island, Niigata Prefecture, are monitored for meteorological and oceanographic conditions by the Japan Coast Guard using an AOV (Nodoguro). We therefore decided to use this observation data to understand the meteorological and oceanographic characteristics of this area.
Offshore winds around Sado generally have speeds around 10 m/s, which is suitable for offshore wind power generation. It was found that wind speeds increase when the wind direction is WNW, NE, or SW. Furthermore, current speeds increased approximately half a day after wind speeds increased.
Offshore Sado, current speeds averaged around 0.4 m/s throughout all layers, with a maximum of approximately 0.6 m/s. Flow conditions can differ near the surface layer and in the lower layer. Therefore, if a floating structure is installed, it may experience different forces at the surface and in the lower layer.
During typhoon approach or passage, wind direction changed slowly, whereas during low-pressure systems, wind direction changed abruptly. Surface flow velocity, wave height, and wind speed were found to increase during typhoon or low-pressure system approach/passage. However, flow velocity did not always increase during the abrupt passage of low-pressure systems. Particularly during low-pressure passage, abrupt changes are likely to occur. Wave height was found to be strongly affected approximately 8 hours after changes in offshore wind speed.
It was determined that multiplying the wave height observation data from the Ministry of Land, Infrastructure, Transport and Tourism's wave observation station off Niigata City (Nowphas Niigata) by approximately 1.6 yields wave heights near the coast of Sado Island.
Looking ahead, it is necessary to conduct more detailed research on the suitability of offshore wind power generation off Sado Island using the findings from this study, such as the approximate linear relationship and wave height ratios.