Imprint of chaotic ocean variability on transports in the southwestern Pacific at interannual timescales
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Published:2021-03-18
Issue:2
Volume:17
Page:487-507
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ISSN:1812-0792
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Container-title:Ocean Science
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language:en
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Short-container-title:Ocean Sci.
Author:
Cravatte SophieORCID, Serazin GuillaumeORCID, Penduff Thierry, Menkes Christophe
Abstract
Abstract. The southwestern Pacific Ocean sits at a bifurcation where southern subtropical
waters are redistributed equatorward and poleward by different ocean
currents. The processes governing the interannual variability of these
currents are not completely understood. This issue is investigated using a
probabilistic modeling strategy that allows disentangling the
atmospherically forced deterministic ocean variability and the chaotic
intrinsic ocean variability. A large ensemble of 50 simulations performed with
the same ocean general circulation model (OGCM) driven by the same realistic
atmospheric forcing and only differing by a small initial perturbation is
analyzed over 1980–2015. Our results show that, in the southwestern Pacific, the
interannual variability of the transports is strongly dominated by chaotic
ocean variability south of 20∘ S. In the tropics, while the
interannual variability of transports and eddy kinetic energy modulation are
largely deterministic and explained by the El Niño–Southern Oscillation (ENSO),
ocean nonlinear processes still explain 10 % to 20 % of
their interannual variance at large scale. Regions of strong chaotic variance
generally coincide with regions of high mesoscale activity, suggesting that a
spontaneous inverse cascade is at work from the mesoscale toward lower frequencies
and larger scales. The spatiotemporal features of the low-frequency oceanic
chaotic variability are complex but spatially coherent within certain
regions. In the Subtropical Countercurrent area, they appear as
interannually varying, zonally elongated alternating current structures, while
in the EAC (East Australian Current) region, they are eddy-shaped. Given this
strong imprint of large-scale chaotic oceanic fluctuations, our results
question the attribution of interannual variability to the atmospheric forcing
in the region from pointwise observations and one-member simulations.
Publisher
Copernicus GmbH
Subject
Cell Biology,Developmental Biology,Embryology,Anatomy
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