Low-frequency turbulence spectra in the mixed layer of Lake Tahoe, California-Nevada

Abstract

Low-frequency turbulence was measured in the unstratified mixed layer (epilimnion) of Lake Tahoe, California-Nevada, during August and September 1973 by using savonius rotor current meters positioned at three depths. Kinetic energy frequency spectra derived from these measurements were compared with the Kolmogorov inertial subrange prediction by assuming that Taylor's hypothesis is valid. The spectra are proportional to (wave number)−5/3 in a wavelength range generally between 10 m and 100 m at all depths. In view of the shallow thermocline depth (18–27 m) the turbulence cannot be considered isotropic in this wavelength range, and a true inertial subrange should not exist. Kinetic energy dissipation rates averaged over the epilimnion were calculated from the −5/3 portion of the kinetic energy spectra and vary between 4×10−4 cm2/s3 (with slight winds) to 5×10−3 cm2/s3 (with winds ranging from 2 to 8 m/s). These dissipation rates are comparable with dissipation rates measured at similar depths in oceanic waters.