Period-doubling sequence in a numerical model of two-layer wind-driven ocean circulation

Abstract

A numerical study is made of a two-layer quasigeostrophic model for a wind-driven subtropical gyre in a square beta-plane basin bounded by no-slip walls. The time series data of basin-averaged potential and kinetic energies are analyzed to examine changes in dynamical regimes when the strength of the steady winds is gradually increased. We have confirmed the following transition from steady to aperiodic states: 1) period-doubling and inverse period-doubling bifurcations associated with mesoscale eddies with a period of several months; 2) the occurrence of an interannual frequency which gives rise to a quasiperiodic state and eventually is phase-locked with the short-term frequencies; and 3) successive period-doubling bifurcations leading to the spectral broadening. Therefore, the decadal variations appearing in the present model may be related with the short-term variations through this sequence including a Feigenbaum scenario.