Dynamics of Large Polymictic Lake. I: Field Observations

The internal dynamics of Clear Lake, California—a large, multibasin and polymictic lake—under stratified conditions is described in this work. Particular attention is paid to one of the subbasins of Clear Lake (Oaks Arm). Several field experiments were conducted in the lake to obtain data of wind, currents, and water temperature using a wide range of devices. Based on field observations and previously published results on basin responses to wind stress, a conceptual model of the internal circulation of the Oaks Arm is proposed. Its internal dynamics are characterized by diurnal cycles of setup and relaxation of horizontal temperature gradients driven by the wind forcing. The setup and relaxation processes are modulated by the influence of the earth’s rotation and create a residual cyclonic circulation. This circulation mechanism is here referred to as baroclinic pumping. It is in all likelihood not exclusive to Clear Lake but probably exists in other large and relatively shallow lakes forced by strong and almost periodic wind events where basin-scale internal waves do not play a major role in the dynamics of the system.