Journal of Fluid Mechanics

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On latency of multiple zonal jets in the oceans

P. Berloffa1 c1, S. Karabasova2, J. T. Farrara3 and I. Kamenkovicha4

a1 Department of Mathematics, Grantham Institute for Climate Change, Imperial College London, London SW7 2AZ, UK

a2 Department of Engineering, Whittle Laboratory, University of Cambridge, Cambridge CB3 0DY, UK

a3 Physical Oceanography Department, Woods Hole Oceanographic Institution, MA 02543, USA

a4 RSMAS, University of Miami, FL 33149, USA

Abstract

Most of the nearly zonal, multiple, alternating jets observed in the oceans are latent, that is, their amplitudes are weak relative to the ambient mesoscale eddies. Yet, relatively strong jets are often observed in dynamical simulations. To explore mechanisms controlling the degree of latency, we analyse solutions of an idealized, eddy-resolving and flat-bottom quasigeostrophic model, in which dynamically generated mesoscale eddies maintain and interact with a set of multiple zonal jets. We find that the degree of the latency is controlled primarily by the bottom friction: the larger the friction parameter, the more latent are the jets; and the degree of the latency is substantial for a realistic range of the oceanic bottom friction coefficient. This result not only provides a plausible explanation for the latency of the oceanic jets, but it may also be relevant to the prominent atmospheric multiple jets observed on giant gas planets, such as Jupiter. We hypothesize that these jets can be so strong because of the relative absence of the bottom friction. The mechanism controlling the latency in our solutions is understood in terms of the changes induced in the linear eigenmodes of the time–mean flow by varying the bottom friction coefficient; these changes, in turn, affect and modify the jets. Effects of large Reynolds numbers on the eddies, jets, and the latency are also discussed.

(Received November 24 2010)

(Reviewed August 06 2011)

(Accepted August 08 2011)

(Online publication September 27 2011)

Key Words:

  • geostrophic turbulence;
  • quasi-geostrophic flows;
  • waves in rotating fluids

Correspondence:

c1 Email address for correspondence: p.berloff@ic.ac.uk

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