Decadal variability of two oceans and an atmosphere

A model of the midlatitude, large-scale interaction between the upper ocean and the troposphere is used to illustrate possible mechanisms of connectio n between the decadal variability in the North Atlantic and in the North Pa cific. The two ocean basins are connected to each other only through their coupling to the common, zonally averaged atmosphere. The ocean-atmosphere c oupling takes place via wind-driven torques and heat fluxes at the air-sea interface. In this formulation, the decadal variability in each ocean basin consists of ocean-atmosphere modes and arises from a delayed feedback of t he upper-ocean heat content onto the wind-driven flow mediated by the atmos phere through the requirements of global heat and momentum balances. The pr esence of two ocean basins leads to three basic kinds of coupling-induced b ehavior: phase locking, oscillation death, and chaos. In the phase-locked r egime, the western boundary currents of the two basins oscillate in synchro ny, with the narrower basin following the wider basin by a small time lag. In the oscillation death solutions, a steady solution is reached, even thou gh each ocean basin, when uncoupled, would have sustained oscillations. In the chaotic regime, the interbasin coupling induces aperiodic fluctuations in both basins characterized by variability at centennial, as well as decad al, timescales.