Wind over stratified water: how accurate is the classical picture?

Session: Physical Processes in Lakes (2)

Marek Stastna, University of Waterloo, [email protected]
Ben Storer, University of Waterloo, [email protected]
David Deepwell, University of Alberta, [email protected]

Abstract

The classical picture of seiche dynamics (both barotropic and internal) states that a wind blowing across the surface of a lake creates a build up of water toward the downwind end of the lake. The lake surface thus tilts upward in the downwind direction, with an opposing (much larger) tilt in the underlying thermocline.  When the wind ceases, the tilt injects energy into both barotropic and internal seiches. We report on a combination of laboratory experiments and numerical simulations of this situation.  In the lab, a fan installed a portion of the tank away from the from the end wall is used to drive air flow over a quasi-two-layer fluid.  Significant turbulence is observed near the forcing, with entrainment of material into the turbulent region.  After a period of adjustment, during which significant wave activity is observed at the pycnocline, a stratification with an upwelled, thicker pycnocline is observed on the upwind side of the tank.   The numerical simulations reproduce the turbulence and entrainment observed in the experiment quite well and allow for a quantitative assessment of the change of pycnocline shape as a function of the across-lake variable.  An exploration of parameter space, especially the Reynolds and Schmidt numbers