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

自由对流翻转期湖流垂向分量的测量由于测量困难，一直没有进行。本文主要在日本山满县的高山山湖志必雷湖进行观测，结果表明，在夜间，水团的垂直交换量增加，而在白天，水团的垂直交换量减少。除了垂直流的日变化外，还记录到一些暂时的波动。这些波动被认为是由平流和内波引起的，水温是了解垂直速度记录的有用元素，但溶解氧只能提供很少的信息。在小型湖泊中，即使在翻转期间，表面温度也有很大变化。因此，垂直速度也有明显的日变化。最大流速通常出现在清晨，约为± 2cm/sec。与水平流相比，这种速度非常慢，但在分析热量和物质交换方面具有重要意义。

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.