To elucidate the changes of the ocean current in connection with global warming and to prevent marine disaster and pollution problems in such a distant area, the development of systems that can precisely identify the fluctuations of the sea such as ocean current in the entire area of the North Pacific Ocean has been called for.
Under the present circumstances, however, there are many difficulties to attain such development because the establishment of complete observation networks in a vast ocean requires enormous time and expenses.
Various kinds of numerical simulations of the ocean are presently under way in order to understand the condition of the ocean which we find difficult to indentify because of the lack of measured values and the incompetency of present measured values. On the other hand, marine numerical models contain various uncertain elements such as basic equations and boundary conditions, thereby making it difficult to analyze the ocean circulation with a sufficient accuracy. Insofar as numerical models are incomplete, therefore, a possible method to obtain more realistic results is to make adjustments by replacing predicted values with observed values.
In this research, numerical simulations using a data assimilation system were conducted in the Pacific Ocean areas to examine the effectiveness of data assimilations on marine fluctuation prediction systems.
The results of the research which has been conducted in relation to the data assimilation system may be summarized as follows:
(1)The objective of flow analysis by the data assimilation system is to determine a flow field by giving a realistic density distribution field based on the measured results while maintaining such a field.
The results of analysis obtained by this system indicate a very high reproducibility as compared with the existing data on surface current which we are currently aware of. The results of analysis on water temperature and salinity distribution fields in the middle layer also agree well with the observed values.
(2)Moreover, in the calculations conducted by tracking sea water particles based on such a system, the results obtained could approximately reproduce the tracking of Algos-buoys, which was carried out in the past, thus supporting the aforementioned reproducibility of flow.
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