Vertical patterns of eddy diffusion during stratification in Castle Lake, California 1

The vertical eddy diffusivity for heat, K z , which characterizes the intensity of vertical mixing, was estimated for depths below the epilimnion in Castle Lake, California, calculated from a series of temperature profiles collected during summer 1972 suitably corrected for solar radiation absorption. K z was usually much larger than the molecular value of diffusivity, indicating that thermal energy is transported in the vertical almost entirely by turbulent mechanisms, even below the epilimnion. Further, K z varied significantly with depth and was well described in the region of high stratification by the form K z = b(N 2 ) m , where m = −0.40 ± 0.02 and N 2 =(Brunt‐Vaisala frequency) 2 , a result close to a previous theoretical prediction.