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 connection between the decadal variability in the North Atlantic and in the North Pacific. The two ocean basins are connected to each other only through their coupling to the common, zonally averaged atmosphere. The ocean-atmosphere coupling 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 the upper-ocean heat content onto the wind-driven flow mediated by the atmosphere through the requirements of global heat and momentum balances. The presence of two ocean basins leads to three basic kinds of coupling-induced behavior: phase locking, oscillation death, and chaos. In the phase-locked regime, the western boundary currents of the two basins oscillate in synchrony, with the narrower basin following the wider basin by a small time lag. In the oscillation death solutions, a steady solution is reached, even though 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 decadal, timescales.