Water circulation in Lake Biwa-ko as deduced from the distribution of water density
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概要
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In this country few studies on the water circulation in lakes have been made so far, although the current is one of the most fundamental factors in physical, chemical, and biological limnology. In Lake Biwa-ko, thirty-six years ago lake currents were surveyed by the staff of Kobe Marine Observatory with the aid of current-meter, afterwards Dr. HIDAKA carried out a series of model experiments. In the last summer, the present authors investigated the current of that lake by drift-bottle method.<BR>On the occasion of the authors, limnological survey in Lake Biwa-ko last autumn, water temperature was observed in the surface and subsurface layers at about 100 stations. Sectional distribution of temperature was found to suggest the existence of water circulation of special mode : a strong thermocline, which developed over the entire lake at about 25 meters below the surface, was inclined or rose considerably as shown in Fig. 2. Remembering that the density of lake water is principally influenced by water temperature, deformation of thermocline should be considered to prove the existence of horizontal pressure gradient in the lake water.<BR>In the present paper, the authors treat the water movement as geostrophic current in two layered waters divided by the thermocline, and for the determination of pressure distribution they draw the depth contours of thermocline corresponding to 15°C isothermal surface (Fig. 1). Current pattern in the upper layer along those contours indicates such directions that deeper contours lie on the right-hand side as the observer looks in the direction of flow, and current velocity is calculated by assuming that pressure gradient equals Coriolis force (taking centrifugal force in some rigions into consideration). In Lake Biwa-ko, two counter-clockwise swirls, velocity of which is about 16 cm/sec, are deduced from the procedures stated above.
- 日本陸水学会の論文
日本陸水学会 | 論文
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