Abstract

<p>The flow of energy in the wind-driven circulation is examined in a <br>combined theoretical and numerical study. Based on a multiple scales <br>analysis of the ocean interior, we find the mesoscale field is strongly <br>affected by the ventilated thermocline, but no feed back from the eddies <br>to the large scale is found.  We then analyze the western boundary <br>region arguing that the associated currents divide between coastal jets, <br>which conserve mean energy, and open ocean, separated jet extensions<br>where the mesoscale is energized by the mean field.   It is the <br>separated jet zone where the primary loss of general circulation energy <br>to the mesoscale occurs.  Connections to the `Thickness Weighted <br>Average' form of the primitive equations are made which support the <br>differing roles of the eddies in these regions.  These ideas are then <br>tested by an analysis of a regional primitive equation 1/12-degree <br>numerical model of the North Atlantic. The predictions of the theory are <br>generally supported by the numerical results.  The one exception is that <br>topographic irregularities in the coastal jet spawn eddies, although <br>they contribute modestly to the energy budget.  We therefore conclude <br>the primary sink of wind input into the mean circulation is in the <br>separated jet, and not the interior.  The analysis also shows<br>wind forcing is much smaller than the interior energy fluxes. Thus, the <br>general circulation is characterized as recirculating energy in the <br>manner of a Fofonoff gyre.</p>

Highlights

  • Based on a multiple-scale analysis, we find the mesoscale field in the ocean interior is strongly affected by, but does not feed back onto, the ventilated thermocline

  • In the western boundary region, the associated currents first appear as coastal jets, conserving mean energy, and later as separated jet extensions where the mesoscale is energized by the mean field

  • The analysis shows wind energy input to be much smaller than the interior energy fluxes; the general circulation largely recirculates energy

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Summary

Introduction

Ocean energy balance have received considerable recent attention, motivated in part by interest in ocean mixing. An early examination is the classic paper by Gill et al (1974), who used a combination of theory and observations to suggest that the interior westward mean flow of the North Atlantic subtropical gyre is an important site for eddy development. The authors argued that the net release from the mean potential energy field to eddies via baroclinic instability appeared to be adequate to balance the net input of energy from the mean wind These estimates were based on local, linearized QG theory. We first provide a short review of past efforts for coupling planetary geostrophic and QG equations leading the main motivations for the present study (Section 2.) A classical multiple-scale analysis of the ocean interior is applied (Section 3 and Appendix A), and argues the local effects of eddies are relatively weak. The paper concludes with a Summary and a discussion of potential future directions (Section 5)

Background
General Circulation Structure and Energy
Regional Dynamics
Energy Considerations
Regional Energy Balances
Numerical Considerations
I xi i I
Model Description
Regional Kinetic Energy Considerations
19.8 GW 41 GW
Potential to Kinetic Energy Conversions
Is the General Circulation Generally Inertial?
Summary
Interior
Interior Energy Vector multiplying B8 by ut and using B9 yields
Coastal Jet
Full Text
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