Laboratory Experiments on Thermally Induced Currents in Lake Biwa

Abstract

Laboratory simulations of the surface gyres which have been stationally observed in Lake Biwa under the stratified condition were conducted by using a rectangular tank of small size and a distorted topographical model. The experimental gyres were generated by heaters installed in water. Through the rectangular tank experiments, the Rossby number, the vertical Ekman number, the densimetric Froude number and the relative upper layer depth were proved to be similar to those of the lake. The distorted model was built taking the similarities of these parameters into account and was employed under heating conditions corresponding to the annual variation of net surface heat (bouyancy) flux. The process of development and decay of the gyres is discussed in relation to heating stratification, and it is shown that the larger scale currents in lakes such as the gyres in Lake Biwa are formed by heat accumulation due to the solar radiation.