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

<p>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 found to enhance greatly lateral dispersion for times less than the inertial period following release. Sub-inertial shear is the dominant mechanism responsible for shear dispersion for times greater than the inertial period. ^ The comparison of drifter and dye release experiments demonstrates the important role of Poincaré wave-induced vertical shear on the dispersion in surface mixed layer. The 3-month observation of surface drifters released at the center of stratified southern basin shows that the surface dispersion can be characterized by three time stages. Although the dispersion rate of the dye patch is slightly lower than Richardson's dispersion, the dispersion rate of the drifter cluster is comparable to Richardson's dispersion only once the drifter cluster reaches the nearshore region. ^ The dissipation rate of turbulence kinetic energy is indirectly estimated through Batchelor spectral fitting using temperature microstructure data. Based on the calculated dissipation rate, the mixing efficiency and vertical eddy diffusivity are parameterized in terms of turbulent dimensionless parameters. The estimated dissipation rate ranged from 10^-9 – 10^-6 <em>m</em>²/<em>s</em>³. The vertical eddy diffusivity is parameterized as order of 10^-8 –10^-5 <em>m</em>²/<em>s</em>.</p>

Name thesis:degree_name

Doctor of Philosophy (PhD)

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Civil Engineering

Year

2015

Author dc:creator

• Choi, Jun M

Contributors dc:contributor

• Dr. Cary D. Troy
• Dr. Dennis Lyn
• Dr. Mathew G. Wells
• Dr. Jun Chen

• Limnology
• Civil Engineering

Repository record dc:identifier

https://docs.lib.purdue.edu/open_access_dissertations/439

OAI identifier oai:identifier

oai:docs.lib.purdue.edu:open_access_dissertations-1276