Study on the variations of vertical flow, Ater temperature and dissoved oxygen during free convection overturn in lake

Research Project

Project/Area Number	60460238
Research Category	Grant-in-Aid for General Scientific Research (B)
Allocation Type	Single-year Grants
Research Field	自然地理学
Research Institution	Rissyo University
Principal Investigator	ARAI Tadashi Professor, Faculty of Letters, Rissyo University, 文学部, 教授 (10062811)
Co-Investigator(Kenkyū-buntansha)	YAMAGUCHI Masanori Associate Professor, General Education Section, Rissyo University, 教養部, 助教授 (00174631)
Project Period (FY)	1985 – 1987
Project Status	Completed (Fiscal Year 1987)
Budget Amount *help	¥2,800,000 (Direct Cost: ¥2,800,000) Fiscal Year 1987: ¥1,400,000 (Direct Cost: ¥1,400,000) Fiscal Year 1986: ¥1,400,000 (Direct Cost: ¥1,400,000)
Keywords	Lake / Convection / Vertical flow / Water temperature / 溶存酸素 / 循環期 / 湖流
Research Abstract	Measurement of the vertical component of lake flow during free-convection overturn period has not been made because of the difficulty in the measurement. This problem was resolved py the application of ultra-sonic current neter, and this device is widely used in this study. Observations were mainly made in Lake Shibire, a saall mountain lake in Yamansshi Prefecture, As expected from the preliminary study, the vertical exchange of water mass increases during night and reduced in daytime. Beseides the daily variation of the vertical flow, some temporary fluctuations were also recorded. These fluctuations are assumed to be induced by advection and internal wave. Water temperature is and useful element in understanding the record of the vertical velocity, but dissolved oxygen affords only a little imformation on this analysis. In small lakes, surface temperature varies considerably even during the over-turn period. Thus the vertical velocity also shows clear diurnal change. Usually, maximun velocity appears in the early morning, and it is about + - 2cm/sec. This velocity is extremaly slow as compared with the horizontal current, but has important significance in analyzing heat and material exchanges.