Three-dimensional baroclinic eddies in the ocean: Evolution, propagation, overall structures, and angular models

Abstract

The evolution and dynamics of an initially Gaussian baroclinic vortex embedded in a resting stratification environment are investigated with a three-dimensional primitive equation model. The vortex evolution process strongly depends on multiple parameters. Particularly, the effects of the gradient of planetary vorticity, nonlinearity, and friction have been studied to evaluate their roles. Comparisons with previous results from a simplified model are made. We particularly focus on interactions between vortices at different levels to understand their evolution. Additionally, a set of numerical simulations has been performed to examine the role of parameter space (Froude–Rossby number) on the evolution of eddies. The evolution and propagation of the vortex is affected by the planetary vorticity gradient; nonlinearity accelerates the transfer of energy from low to high angular mode and speeds up the propagation of eddies. A new finding is that a ‘‘double dipole’’ structure is observed with the development of a vortex, which is located in the core and edge regions, respectively. Only eddies in a finite depth range can maintain synchronous motion, and the dispersive translation paths in all levels imply that initially aligned eddies finally develop into misaligned structures and lead the tilted axis. In contrast to the results in a previous study, eddies have a southward drift irrespective of the vortex polarity. The eddies in the upper level maintain strong stability; in the middle depths, eddies decay rapidly where they form mixed barotropic and baroclinic instabilities. The energy budget analysis demonstrates the complex energy conversion between eddy and angular modes. The Burger number is the most important factor affecting the pattern of eddy evolution.