SAMPLING OF INTERNAL WAVES AND NATURAL CONVECTION IN A RESERVOIR BASED ON WATER TEMPERATURE MEASUREMENTS

Reservoir water temperature was measured simultaneously at vertical multi-points using a thirty-channel thermistor chain. Data were collected every 10.5-second in order to detect even short time-scale motions. The objective is to make investigation on internal waves and natural convective motions that are much responsible for turbulent energy transfer as well as for water mass transport. Internal wave propagation was examined by filtering time series of water temperature and a cross-correlation analysis. A propagation diagram in a spacetime coordinate system successfully described scales, modes and propagation characteristics of internal waves. Natural convection was investigated by analyzing dataset collected during winter nights. A conditional sampling, VITA-Variational Interval Time Averaging-was applied to detect organized motions due to nocturnal cooling. From conditionally averaged time series of temperature, a velocity scale of natural convection was obtained, which well agreed with the Deardorff's velocity scale. Entrainment rate and vertical turbulent heat flux were evaluated, which were well correlated to those found in small-scale experimental models.