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On the dynamics of the Atlantic meridional overturning circulation in idealized models forced by differential heating and winds

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Title:On the dynamics of the Atlantic meridional overturning circulation in idealized models forced by differential heating and winds
Authors:Schloesser, Fabian
Date Issued:Dec 2011
Publisher:[Honolulu] : [University of Hawaii at Manoa], [December 2011]
Abstract:Historically, ocean models and solutions of different complexity have been developed to investigate the dynamics of basin-scale, deep, meridional overturning circulations (MOCs). In this study, we develop a three-dimensional theory for the descending branch of the MOC in solutions near the bottom of the hierarchy, forced only by a surface buoyancy flux and a zonal wind stress.
Our theory is based on analytical solutions for a variable-density, layer ocean model (VLOM). The results are validated by comparing the VLOM solutions to numerical solutions to an ocean general circulation model (MITgcm).
Key processes that determine the strength and structure of the model MOC are the following. The eastern-boundary upper-layer thickness is determined by a no-flow condition normal to the boundary, which implies a poleward deepening of the thermocline in response to the meridional surface density gradient. The baroclinic Rossby-wave speed in VLOM illustrates how the large-scale surface density gradient aggects the propagation of Rossby waves, which adjust the interior-ocean layer thickness. In a narrow, northern region, the upper layer with a vertically uniform temperature is very thick, and Rossby waves are damped by mixing processes, which tend to restratify the water column.
In solutions without winds, the Rossby-wave damping is the main mechanism to generate a northward convergence of upper-layer flow, and to establish the sinking branch of the MOC. In solutions with winds, water also detrains in the interior subpolar gyre, as it is cooled on its way north, and is finally reaches the deep-ocean temperature.
We derive analytical expressions for MOC transports in VLOM that depend on the tropical thermocline depth, the meridional density gradient, the strength of the mixing and the wind forcing. These results recover and provide dynamical explanations for scaling laws that relate the strength of the MOC to the meridional pressure difference.
Description:Ph.D. University of Hawaii at Manoa 2011.
Includes bibliographical references.
Appears in Collections: Ph.D. - Oceanography

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