Intrinsic low-frequency variability in the global turbulent ocean: key features from "realistic" simulations

• Author: Thierry Penduff, CNRS - LEGI.


• Names of other authors: Mélanie Juza, Bernard Barnier, Jan Zika, William K. Dewar, Anne-Marie Treguier, Jean-Marc Molines, Nicole Audiffren.


• Oral or poster: oral.


• Downloadable abstract: click here.


• Abstract:
  Idealized simulations show that constantly-forced eddying ocean models intrinsically generate low-frequency (interannual-to-decadal) variability in eddy-active regions. We aim to quantify from realistic, global eddying ocean simulations the imprint of this intrinsic interannual variability on climate-relevant quantities, e.g. sea-level anomalies (SLA), sea-surface temperature (SST), mixed-layer depth (MLD), and meridional overturning circulation (MOC).
  Comparing two 1/4° global ocean simulations driven by (i) the full range of atmospheric timescales and (ii) a repeated seasonal cycle reveals that the intrinsic part of the total interannual SLA variance exceeds 40% over half of the open ocean area, and exceeds 80% over one fifth of it (Southern Ocean, western boundary currents). This proportion is also large on SST and MLD, suggesting potential atmospheric and biogeochemical consequences of this oceanic phenomenon. Note that no intrinsic variability appears in coarse-resolution ocean models, which are presently used in coupled mode for IPCC climate prediction. The contribution of intrinsic/chaotic processes in the total low-frequency MOC variability is also presented. These results suggest that eddying ocean models used in future climate predictions will yield a more chaotic variability, and call for the investigation of these nonlinear processes in "realistic" ocean simulations.