ON THE INFLUENCE OF DIURNAL THERMAL STRATIFICATION ON WIND-DRIVEN CURRENT

Hourly measurements of water temperature and velocity were taken in Lake Kasumigaura (36N, 140E, 1m a. s. l.) to study the influence of diurnal thermal stratification on the flow and mixing in shallow temperate lakes in summer.The vertical profile of wind-driven current is discussed with the emphasis on the effect of the diurnal thermal structure, and the erosion of diurnal thermal structure is discussed with the emphasis on the effect of the shear at the bottom of the mixed layer which is caused by wind-driven currents.A simple numerical model of the interplay between diurnal thermal stratification and wind-driven current is developed and tested using observed temperature and velocity profiles for verification. The model successfully reproduces hourly variations of the mixed layer thickness and velocities above and below the thermocline.