A model for forecasting water temperature of a small bay at Sanriku coast

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To develop a model for forecasting water temperature of a small bay, Otsuchi Bay, located at the Sanriku coast of Japan, we clarified physical process of the bay, such as heat balance, water circulation, turbulent activity and so on. We first investigated inter-annual variation of heat budget through the sea surface of the bay by using weather and sea condition data supplied by International Coastal Research Center, the University of Tokyo and neighborhood meteorological stations, the Japan meteorological agency. The results show a clear difference in heat budget between the 80' and 90'. This difference is attributed to differences in both downward shortwave radiation and wind speed in Tohoku area. Second, we have carried out a measurement of turbulent activity both at the bay mouth and inner bay. The energy dissipation rate is estimated at the order of 10^<-7> to 10^<-8> W/kg in general, but sometimes up to the order of 10^<-6> W/kg at the depth of 15 to 20m of the inner bay. Third, we simulated wind driven water circulation by using GETM (General Estuarine Transport Model). The results are compared quite well with the circulation pattern obtained by the observational results. The vertical circulation caused by westerly in winter season shows the out flow above the depth of 8-10m and inflow below it. We also tried to investigate a statistical model for forecasting water temperature of the bay. On the basis of the data from 1978 to 2003, statistical coefficients of AR (Auto Regressive model) and ARMA (Moving Average of Auto Regressive model) are estimated. By using these coefficients, we calculated water temperature variation in 2004. As a result, this model forecasts water temperature of the bay with the bias of 0.58℃ and standard deviation of 0.88℃.