Stochastic variability of oceanic flows above topography anomalies

TL;DR

This paper identifies a stochastic internal variability mechanism in oceanic flows caused by topography and eddy activity, explaining large fluctuations like those of the Zapiola anticyclone through long-term simulations.

Contribution

It introduces a new internal stochastic variability mechanism linked to topography and eddy activity, supported by a 310-year global ocean model simulation.

Findings

Vortex formation above topography anomalies causes significant variability.

Eddy-driven stochastic variability influences large-scale ocean transport.

Long-term simulation supports the mechanism's relevance to observed fluctuations.

Abstract

We describe a 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 strong interannual fluctuations of the transport of the Zapiola anticyclone ($\sim 100 \ Sv$) in the Argentine basin are argued to be partly due to such eddy-driven stochastic variability, on the basis of a 310 years long simulation of a comprehensive global ocean model run driven by a repeated-year forcing.