Stochastic variability of large-scale oceanic flows above topography anomalies

Antoine Venaille (1) , Julien Le Sommer (2) , J.-M. Molines (2) , B. Barnier (2)

1 GFDL - NOAA Geophysical Fluid Dynamics Laboratory
2 LEGI - Laboratoire des Écoulements Géophysiques et Industriels [Grenoble]

Large-scale oceanic currents show large fluctuations at decadal, centennial and even millennial time scales. Here, we describe a new stochastic variability mechanism which is genuinely internal to the ocean, i.e. not due to fluctuations in atmospheric forcing. The key ingredient is the existence of closed contours of bottom topography surrounded by a stirring region of enhanced eddy activity. This configuration leads to the formation of a robust but highly variable vortex above the topography anomaly. The vortex dynamics integrates the white noise forcing of oceanic eddies into a red noise signal for the large scale volume transport of the vortex. The fluctuations of the transport of the Zapiola anticyclone (100 Sv) in the Argentine basin are argued to be an example of such eddy-driven stochastic variability, on the basis of a 310 years long simulation of a comprehensive ocean model run driven by a repeated-year forcing.

Domaines: Physique Atmosphérique et Océanique [physics.ao-ph]

Antoine Venaille, Julien Le Sommer, J.-M. Molines, B. Barnier. Stochastic variability of large-scale oceanic flows above topography anomalies. 2011. ⟨hal-00577907v1⟩