Control of Decadal and Bidecadal Climate Variability in the Tropical Pacific by the Off-Equatorial South Pacific Ocean

Abstract

elayed negative feedback processes determining intrinsic decadal and bidecadal time scales for the tropical variability in the Pacific are investigated based on climate model experiments. By comparing a control run driven by preindustrial forcing and partial blocking runs driven by the same forcing but with ocean temperature and salinity restored to climatology in selected regions, subsurface oceanic signals of South Pacific origin are shown to precede SST variability in the Niño-3.4 region. Using a linear reduced-gravity ocean model driven only by wind stress changes and an offline tracer model, oceanic wave adjustment triggered by changes of wind stress curl in the South Pacific extratropics is suggested to be essential for the decadal component of the equatorial SST, while slower isopycnal advection of subsurface temperature anomalies from the formation region of South Pacific Eastern Subtropical Mode Water controls the bidecadal component. The intrinsic time scales of the tropical variability are regulated by simple linear ocean dynamics.