Near-inertial internal Poincare waves in Lake Michigan: Seasonal variability and effects on lateral dispersion and turbulent mixing

Choi, Jun M. Ph.D., Purdue University, May 2015. Near-inertial internal Poincaré waves in Lake Michigan: Seasonal variability and effects on lateral dispersion and turbulent mixing. Major Professor: Cary D. Troy. A dominant physical process in stratified Lake Michigan is near-inertial internal Poincaré waves. The near-inertial internal Poincaré waves is described as locally quasi-uniform currents in the lateral direction, with vertically-sheared structures rotating clockwise at a near-inertial period. The goal of this dissertation is to investigate their seasonal variation and the potential roles on lateral dispersion and vertical mixing. At this mid-lake location, the Poincaré wave is seen to describe more than 80% of the observed surface current variability for much of the year, with characteristic near-inertial frequency and clockwise-rotating velocities. The wave persists during the stratified period, and is supported by as few as 1-2 degrees of thermal stratification over 150m. The strongest Poincaré wave activity is seen to correspond to the period of strongest summer thermal stratification. The vertical shear created by near-inertial internal Poincaré waves is not only an energy source for vertical mixing in the thermocline and mixed layer, but also enhances horizontal dispersion via an unsteady shear flow dispersion mechanism. The Poincaré waves are