Study on the Kyucho in the Bungo Channel

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Investigations were made on the Kyucho in the Bungo Channel. Its structure, periodicity of its generation, mechanism of its generation and its influences on the marine environment were studied by the field observations, such as long term monitoring of water temperature and CDT surveys, and analyses of the historical data. The following results were obtained.(1) The Kyucho in the Bungo Channel is a phenomenon of the intrusion of a warm, lighter water mass from the Pacific Ocean, and is fundamentally a gravity current. The warm water mass intrudes into eastern half of the channel looking the coast to its right side. (2) The Kyucho appears around neap tide. (3) The Kyucho appears mainly around summer. (4) Generation of the Kyucho is determined by the variation of the intensity of vertical mixing. But quantitative examination of the vertical mixing suggested that some other mechanism must work in addition to this effect. (5) The intensities of the Kyucho is influenced by the oceanic disturbances. The Kyucho is intensified when the supply of warm water mass from the ocean to the southern part of the Bungo Channel falls on neap tide. (6) The Kyucho gives many influences on the marine cultures along the eastern coast of the Bungo Channel such as disease or decease of the cultured fish due to the sudden change of water temperature. On the other hand, the Kyucho contributes to the renewal of the bay water maintaining water quality, and supports the large scale cultures.Study on the generation mechanism including the effect of earth's rotation is necessary in future.