Swell-dominant surface waves observed by a moored buoy with a GPS wave sensor in Otsuchi Bay, a ria in Sanriku, Japan
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Real-time monitoring of wind and surface waves in Otsuchi Bay, Iwate, Tohoku, Japan, commenced in October 2012, using a mooring buoy with an ultrasonic anemometer and a single-mode GPS wave sensor. Wind and wave data are distributed hourly in real time via the Internet along with a chart of their time series. We analyzed data monitored in the first 3 months in order to assess the variability and occurrence of wind and waves and to elucidate the main reasons for wave variation in Otsuchi Bay. The monitoring data revealed that surface waves in the bay were predominantly affected by swells propagated from the northeastern offshore region and that the wave height was significantly correlated with the component of wind velocity toward Otsuchi Bay in the northeastern offshore region that faces the bay mouth. The offshore wind field was expected to provide information useful for predicting coastal waves in a ria bay in Sanriku such as Otsuchi Bay. However, it should be emphasized that the horizontal distribution of the offshore wind field which has a significant effect on the surface waves in a ria bay depends heavily on the topographic shape of the bay.
KeywordsSurface wave Otsuchi Bay GPS wave sensor Swell Ria coast
The authors would like to express their great appreciation to K. Kogure and A. Tsuda for their encouraging promotion of this study. We also are deeply appreciative of the Kamaishi-Tobu Fishermen’s cooperative association (I. Ogawara, President) for providing facilities to moor the buoy in close vicinity to their aquaculture systems for the brown seaweed wakame. Mooring and maintenance of the buoy have been enormously supported by M. Kurosawa, M. Hirano, T. Suzuki, and other staff of the International Coastal Research Center, the Atmosphere and Ocean Research Institute at the University of Tokyo. We are also appreciative of the Shin-Otsuchi Fishermen’s cooperative association and the Iwate Fisheries Technology Center for their helpful advice on operating the buoy. Wave data recorded by the NOWPHAS were downloaded from its website (http://www.mlit.go.jp/kowan/nowphas/), and sea–wind data simulated by the Japanese Meteorological Agency were from the data server of the GFD Dennou Club (http://database.rish.kyoto-u.ac.jp/arch/jmadata/data/gpv/netcdf/). Some of the figures were drawn using information from the GFD Dennou Library. Financial support for this study was provided by the Tohoku Ecosystem-Associated Marine Sciences, subsidized by the Ministry of Education, Culture, Sports, Science and Technology.
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