University of Minnesota
Aerospace Engineering and Mechanics
Fall 2000 Seminar Series



Mechanics, mixing, and patterns in the ocean surface layer


Professor Sidney Leibovich

Sibley School of Mechanical and Aerospace Engineering, Cornell University


Abstract

The heat content of the planet is strongly mediated by the ocean surface mixed layer, a relatively thin water layer at the air-sea interface. It is not an exaggeration to describe this region as the thermal flywheel for our planet. Furthermore, by its dominating effect on the balance of greenhouse gases, this thin layer does much to dictate the future course of global warming, given a prescribed global production of greenhouse gases.

Wind--generated stirring of the ocean surface and of lakes and ponds inevitably occurs in the presence of surface gravity waves. Waves can modify the turbulence and especially the mixing in significant ways. Energetic, persistent coherent motions discovered by Irving Langmuir can occur under these circumstances. These motions often mark the water surface with bold persistent patterns and can be explained by an instability mechanism due to the interaction of the waves and shear. This mechanics underlying this instability and the Langmuir circulation consequences are described.

Langmuir patterns resemble the coherent structures appearing in "ordinary" turbulent boundary layers, but they are of much larger scale and persistence. Turbulent vertical stirring in is much greater when Langmuir circulation is present. We describe the wave--induced predicted to occur by a large eddy simulation.

Pattern evolution occurs in large aspect ratio situations and is not amenable to computation from the full model equations. Simulations of amplitude equations constructed from the full equations by perturbation methods are useful in this context, and will be described.

Friday, November 3, 2000
209 Akerman Hall
2:30-3:30 p.m.


Refreshments served after the seminar in 227 Akerman Hall.
Disability accomodations provided upon request.
Contact Kristal Belisle, at (612) 625-8000.