Diagnostics of isopycnal mixing in a circumpolar channel ...

• Main Authors: Abernathey, Ryan Patrick, Ferreira, David, Klocker, Andreas
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Columbia University 2013
• Subjects: Eddies; Oceanic mixing > Mathematical models; Diffusion; Ocean circulation; Oceanography; FOS: Earth and related environmental sciences; Antarctic; The Antarctic; Antarc*
• Online Access: https://dx.doi.org/10.7916/d81c1wsk; https://academiccommons.columbia.edu/doi/10.7916/D81C1WSK

Mesoscale eddies mix tracers along isopycnals and horizontally at the sea surface. This paper compares different methods of diagnosing eddy mixing rates in an idealized, eddy-resolving model of a channel flow meant to resemble the Antarctic Circumpolar Current. The first set of methods, the “perfect” diagnostics, are techniques suitable only to numerical models, in which detailed synoptic data is available. The perfect diagnostic include flux-gradient diffusivities of buoyancy, QGPV, and Ertel PV; Nakamura effective diffusivity; and the four-element diffusivity tensor calculated from an ensemble of passive tracers. These diagnostics reveal a consistent picture of isopycnal mixing by eddies, with a pronounced maximum near 1000 m depth. The isopycnal diffusivity differs from the buoyancy diffusivity, a.k.a. the Gent–McWilliams transfer coefficient, which is weaker and peaks near the surface and bottom. The second set of methods are observationally “practical” diagnostics. They involve monitoring the spreading ...