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Weekly Seminar: Spring 2012

Speaker: Dr. Kial Stewart (JHU | EPS)
Title: "The Effects of Turbulent Mixing on an Overturning Circulation"

Date: Friday, February 17, 2012
Time: 11:00 a.m.
Location: Gilman Hall 50 (Marjorie M. Fisher Hall)

Abstract

Turbulent mixing is thought to influence the ocean meridional overturning circulation (MOC), however a detailed physical understanding of the coupling between mixing and the MOC is yet to emerge. This coupling is examined through idealized laboratory experiments with a convective overturning driven by an applied salt flux at the surface. Additional mechanical mixing was imposed using horizontal rods that are yo-yoed continuously through the water column. The resulting density stratification and overturning rate were, for large rod velocities, found to be consistent with an existing theoretical model. The overturning rate increased with increasing mixing rates. The total diffusivity is parameterized and it is found that for weak (or no) externally imposed stirring the convection itself maintained an apparent background vertical diffusivity that is 100 times larger than the molecular level, outweighing the externally forced mixing. Insights into relevant mechanisms governing ocean mixing and stratification will be discussed.

 

Bio

Kial Stewart is a postdoc at Earth & Planetary Sciences, JHU after recently completing his PhD in Earth Physics at The Australian National University. His research relates to buoyancy-driven flows, in particular the role of buoyancy forcing in the overturning circulation of the ocean. He is Interested in the effects of turbulent mixing on ocean circulation and energetics.