Summer Circulation and Temperature Structure of Lake Kinneret

Abstract

A three-dimensional lake model driven by wind stress and heat flux fields derived from an atmospheric model is applied to Lake Kinneret, Israel. The summer wind field over the lake has a strong diurnal and large spatial variation due to complex terrain surrounding the lake, the sharp temperature contrast between the arid land and the lake, and due to the penetration of the Mediterranean sea breeze (MSB) into the lake area. The daily mean wind curl field, which is predominantly determined by the penetration of the MSB, is responsible for the generation of three lake gyres. One of them dominates most of the lake and rotates counterclockwise. It is flanked to the north and to the south by two smaller ones that rotate clockwise. During the summer, the diurnal variation of the wind over the lake is repeated daily due to consistent forcing conditions during that season. Numerical tests show that the rectified flow induced by the diurnal winds plays a minor role in the lake circulation. The thermocline oscillation, which was believed to be the free propagation of internal Kelvin waves, mainly responds to the surface elevation set up by the time-dependent winds, and it appears that no systematic counterclockwise propagating waves with large thermocline displacements exist in the lake. The intense MSB over the lake in the late afternoon pushes the heated surface water toward the east, forcing the deep cooler water to be advected westward, and creating strong mixing over the shallow western shore. This results in higher temperature off the eastern shore and lower temperature off the western shore. However, a strong mean flow is constantly eliminating the temperature difference by counterclockwise transfer of the western cooler water eastward. The results are in good agreement with available observations.