Multiple Equilibria and Low-Frequency Variability of Wind-Driven Ocean Models.
Abstract
The steady states of the double-gyre wind-driven model are studied. It is shown that both stable and unstable fixed points influence the shape of the model's attractor in phase space. The bifurcation away from a unique and stable steady state are mapped as a function of the explicit damping in the model. A highly inertial branch characterized by a circulation with transports far in excess of those predicted by Sverdrup balance is present over a wide range of parameters This branch is anti-symmetric with respect to the mid-basin latitude. Additional pairs of mirror image non-symmetric equilibria exist. These equilibria have currents which redistribute relative vorticity across the line of zero wind-stress curl. This redistribution of vorticity prevents the solution from developing the large transports that are necessary for the anfl-symmetric solution to achieve a global vorticity balance. The successive pairs of non-symmetric equilibria come into existence via symmetry-breaking pitchfork bifurcation as the model's viscosity is reduced. Each new pair of equilibria has an additional half meander in the jet. A significant fraction of the low frequency variance in the time-dependent simulations is captured by coherent structures which point away from the time-mean state and towards the fixed points in phase space.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 01, 1998
- Accession Number
- ADA369289
Entities
People
- Francois W. Primeau
Organizations
- Woods Hole Oceanographic Institution