Mutually Interactive Decadal-timescale Processes Connecting the Tropical Atlantic and Pacific (Invited)

Tuesday, December 10, 2019 - 13:40
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Decadal climate prediction presumes there are relevant processes and mechanisms that, if initialized properly, could provide predictive skill beyond the first year or two. Candidate mechanisms involve Pacific Decadal Variability (PDV, e.g. the Interdecadal Pacific Oscillation, IPO), and Atlantic Multidecadal Variability (AMV, e.g the Atlantic Multidecadal Oscillation, AMO). If one is driving the other, then a skillful prediction of decadal variability in one basin would result in skillful predictions of SST in the other basin. Resulting global-scale teleconnections would then simplify the decadal climate prediction problem. Pacemaker model configurations are run in separate experiments first with specified idealized patterns of decadal-timescale SSTs for AMV and PDV, with the rest of the model fully coupled. Additional pacemaker experiments are run with observed time-evolving SSTs in the Pacific and Atlantic. In the idealized AMV pacemaker experiment, there tends to be a weak opposite-sign PDV response in the tropical Pacific. Conversely, for the idealized PDV experiment, there is a weak same-sign AMV response in the tropical Atlantic. Both tropical basins are connected through the atmosphere by the large-scale east-west Walker Circulation. Net surface heat flux in the Atlantic and ocean dynamics in the Pacific play contrasting roles in the ocean response in the respective basins. We propose a new paradigm for decadal timescale variability such that processes in the Pacific and Atlantic are mutually interactive through the atmospheric Walker Circulation. This result implies that processes and mechanisms in both basins, and their interations, must be simulated to produce credible decadal climate predictions.

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