Time Variation of Water Temperature in Lake Biwa-ko (III):Drastic change of temperature accompanied with the intrusion of deep water

概要

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A drastic change of water temperature which amounted up to 8°C in the bottom layer was by chance found in the southern basin of Lake Biwa-ko during the period of routine observation in August 1967. At the same time, an automatic recorder for water temperature installed at Biwa-ko Ohashi Bridge caught a remarkable variation of temperature. On analyzing the records, two kinds of oscillatory change have been indicated. One of them, whose period is 4 hours, is caused by an ordinary seiche on the occasion of horizontal gradient of temperature existing in that region. The other, which has a period of 43 hours with an amplitude of 4°C, may be caused by an internal seiche in the northern basin, because its period is computed at 42 hours on assuming a free uninodal oscillation of two layers. Successive measurements of the water current performed at the fixed station have shown that the no-flow level between the upper layer flowing northwards and the lower layer flowing southwards has gradually ascended together with the rise of thermocline level. A remarkable depression of temperature observed in the southern basin occurred owing to the intrusion of cold deep water of the northern basin accompanied with an internal seiche mentioned above. The water volume of the intrusion is calculated at 4×107m3, on the assumption of the conservation of water mass and of heat content.
日本陸水学会の論文