Estimating internal waves and diapycnal mixing from conventional mooring data in a lake

A methodology is described to analyze and interpret the temporal variations of temperature and current measured in lakes or on the continental shelf by generally available standard and robust equipment, a single thermistor chain, and current meters. It is assumed that variations are mainly produced by internal wave modes propagating in the mean flow and mean stratification. The analysis provides estimates of the propagation characteristics, energy density, and directional flux of the internal waves, as well as the temporal and vertical distribution of Richardson number, Ri, on scales that may be smaller than those separating the measuring instruments. The method is tested with measurements made in Lake Geneva, and provides realistic quantitative estimates of the rate of dissipation of turbulent kinetic energy per unit mass, epsilon, and of the vertical diffusivity, K-v, which are useful in establishing the processes leading to diapycnal mixing.