Generation of Mid-Ocean Eddies: The Local Baroclinic Instability Hypothesis
Abstract
The plausibility of local baroclinic instability as a generation mechanism for mid-ocean mesoscale eddies is examined with a two-layer, quasi-geostrophic (QG) model forced by an imposed, horizontally homogeneous, vertically sheared mean flow and dissipated through Ekman friction. The effects of stratification and Ekman friction on the inverse cascade to the barotropic mode and to scales larger than the deformation radius are examined. When stratification is surface-trapped and friction occurs only in the bottom layer, eddies can be simultaneously near the deformation radius and strongly baroclinic, in accordance with observations. A systematic study of geostrophic turbulence forced by nonzonal flows on a beta plane is also performed. Nonzonality allows substantial eddy energy to be generated even when beta is larger than shear-induced potential vorticity gradients, but in that case eddy fields are anisotropic, unlike those in the ocean. Isotropic eddies are produced when beta is less than shear-induced gradients. When, in addition, the mean shear has a westward zonal component, fields of monopolar vortices form and persist, Energy is asymmetric between fields of cyclones and anticyclones. Such asymmetry was commonly thought not to occur in QG, but is introduced here by the nonzonal basic state.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 2000
- Accession Number
- ADA384924
Entities
People
- Brian K. Arbic
Organizations
- Massachusetts Institute of Technology