Near-inertial internal waves are ubiquitous features in both large lakes and oceans. In large thermally-stratified lakes such as Lake Michigan, these basin-scale waves create strong near-surface currents that rotate clockwise (in the northern hemisphere) over a near-inertial period (~17.5 hours for Lake Michigan). The influence of these basin-scale waves, for which the thermocline movement represents a spinning coin, is particularly strong in the offshore waters, where the spiraling near-surface currents can have tide-like regularity, with magnitudes exceeding 50 cm/s. While these waves are readily observed in velocity and temperature measurements taken in large lakes, their influence on vertical mixing and lateral dispersion is not well-understood. This project examines two related hypotheses: (1) strong near-inertial shear drives cross-thermocline mixing; (2) lateral dispersion is enhanced by vertical shear associated with near-inertial wave currents. Our approach for this project is to carry out a set of field measurements involving moored instruments and microstructure cruises, as well as a large-scale dye and drifter release carried out in the center of Lake Michigan’s southern basin.
National Science Foundation, Division of Ocean Sciences, Physical Oceanography Program
Nathan Hawley, NOAA Great Lakes Environmental Research Laboratory
Cross-shelf thermal structure in Lake Michigan during the stratified periods
Troy, C.D., Ahmed, S., Hawley, N., and A. Goodwell Journal of Geophysical Research, VOL. 117, C02028, 16 PP., 2012 PDF Online Article