David Marshall

Abstract:

Oceanic Rossby waves and eddies flux energy and fluid westward, the latter through the Stokes drift or bolus transport. While the wave energy is largely dissipated at the western boundary, mass conservation requires that the fluid be returned offshore through Rossby rip currents. The form and magnitude of these rip currents are investigated through linear Rossby wave theory, a nonlinear numerical model, and analysis of sea surface height satellite observations. The net eastward volume transport by Rossby rip currents over the global ocean is estimated to be of order 10 Sv (1 Sv ≡106 m3 s -1). In an eddying ocean, both the westward Stokes drift and eastward rip currents can assume the form of banded quasi-zonal jets. Key Points Oceanic Rossby waves and eddies carry a westward Stokes drift The westward Stokes drift may be compensated by eastward Rossby rip currents Both the Stokes drift and rip currents can assume the form of banded zonal jets. © 2013. American Geophysical Union. All Rights Reserved.

Abstract:

Conceptual models are a vital tool for understanding the processes that maintain the global ocean circulation, both in nature and in complex numerical ocean models. In this chapter we provide a broad overview of our conceptual understanding of the wind-driven circulation, the thermohaline circulation, and their transient behavior. While our conceptual understanding of the time-mean wind-driven circulation is now fairly mature, basic questions remain regarding the thermohaline circulation, for example, surrounding its overall strength and stability. Similarly, basic questions remain regarding the transient adjustment and internal variability of the ocean circulation. © 2013 Elsevier Ltd.

Abstract:

The aim of this paper it to derive general coordinate-invariant forms of the Eliassen-Palm flux tensor and thereby characterize the true geometric nature of the eddy-mean-flow interaction in hydrostatic Boussinesq rotating fluids. In the quasi-geostrophic limit previous forms of the Eliassen-Palm flux tensor are shown to be related to each other via a gauge transformation; a general form is stated and its geometric properties are discussed. Similar methodology is applied to the hydrostatic Boussinesq Navier-Stokes equations to re-derive the residual-mean equations in a coordinate-invariant form. Thickness-weighted averaging in buoyancy coordinates is carefully described, via the definition of a volume-form-weighted average, constructed so as to commute with the covariant divergence of a vector. The procedures leading to the thickness-weight averaged equation are discussed, and forms of the Eliassen-Palm flux tensor which arise are identified. © 2013 Cambridge University Press.

Abstract:

We use a sector con guration of an ocean general circulation model to examine the sensitivity of circumpolar transport and meridional overturning to changes in Southern Ocean wind stress and global diapycnal mixing. We nd that at eddy-permitting, and ner, resolution the sensitivity of circumpolar transport to forcing magnitude is drastically reduced. At su ciently high resolution, there is little or no sensitivity to wind stress, even in the limit of no wind. In contrast, the meridional overturning circulation continues to vary with Southern Ocean wind stress, but with reduced sensitivity in the limit of high wind stress. We nd that both the circumpolar transport and meridional overturning continue to vary with diapycnal di usivity at all model resolutions. The circumpolar transport becomes less sensitive to changes in diapycnal di usivity at higher resolution, although sensitivity always remains. In contrast, the overturning circulation is more sensitive to change in diapycnal di usivity when the resolution is high enough to permit mesoscale eddies. These models cast doubt upon the validity of climate projections obtained using non-eddy-resolving ocean models.