Global prediction of abyssal hill root‐mean‐square heights from small‐scale altimetric gravity variability

Goff, John A.

doi:10.1029/2010jb007867

Cited by 50 publications

(128 citation statements)

References 45 publications

(118 reference statements)

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“…Building upon the work of Goff and Jordan [], Goff and Arbic [] estimated abyssal hill statistical parameters globally using empirical relationships derived previously between seafloor spreading rate and direction, while taking into account the smoothing effects of sediment cover. Goff [] then formulated an alternative representation of global abyssal hill statistics over a larger domain of the ocean based primarily on the small‐scale roughness of the gravity field measured by satellite altimeters. Although both can be considered realistic renderings, the latter is considered to be more accurate, particularly in more heavily sedimented regions [ Goff , ], such as the Kerguelen Plateau examined by Waterman et al .…”

Section: Lee Wave Closuresmentioning

confidence: 99%

Internal lee wave closures: Parameter sensitivity and comparison to observations

et al. 2015

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This paper examines two internal lee wave closures that have been used together with ocean models to predict the time‐averaged global energy conversion rate into lee waves and dissipation rate associated with lee waves and topographic blocking: the Garner (2005) scheme and the Bell (1975) theory. The closure predictions in two Southern Ocean regions where geostrophic flows dominate over tides are examined and compared to microstructure profiler observations of the turbulent kinetic energy dissipation rate, where the latter are assumed to reflect the dissipation associated with topographic blocking and generated lee wave energy. It is shown that when applied to these Southern Ocean regions, the two closures differ most in their treatment of topographic blocking. For several reasons, pointwise validation of the closures is not possible using existing observations, but horizontally averaged comparisons between closure predictions and observations are made. When anisotropy of the underlying topography is accounted for, the two horizontally averaged closure predictions near the seafloor are approximately equal. The dissipation associated with topographic blocking is predicted by the Garner (2005) scheme to account for the majority of the depth‐integrated dissipation over the bottom 1000 m of the water column, where the horizontally averaged predictions lie well within the spatial variability of the horizontally averaged observations. Simplifications made by the Garner (2005) scheme that are inappropriate for the oceanic context, together with imperfect observational information, can partially account for the prediction‐observation disagreement, particularly in the upper water column.

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Section: Lee Wave Closuresmentioning

confidence: 99%

Internal lee wave closures: Parameter sensitivity and comparison to observations

et al. 2015

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“…Above this scale, sea floor features do not appreciably increase in height as their lateral scale increases. The upper limit of the self-affine regime can be thought of as a ''characteristic scale'' of the topography (Goff and Jordan 1988). If we assume that, in the selfaffine regime, the skirt length L T is approximately a constant proportion of ''feature length'' (L x and L y ), then Eq.…”

Section: A Wind Stressmentioning

confidence: 99%

“…A major difficulty in understanding the role of smallscale topography in arresting the ocean circulation is that abyssal hill scales cannot be resolved by conventional global topographic datasets, which are largely reliant on satellite altimetric gravity measurements and have a characteristic horizontal resolution of 10-20 km (e.g., Smith and Sandwell 2004). In the present work, we take advantage of the recent development of two quasiindependent, near-global datasets of small-scale topographic parameters by Goff and Arbic (2010) and Goff (2010) (respectively referred to as GA2010 and G2010 hereafter) verified by comparison with available multibeam bathymetric observations. The GA2010 dataset predicts abyssal hill roughness statistical parameters via relationships for the average statistical properties of abyssal hills as a function of spreading rate and direction, and for the modification to these roughness parameters as a function of sediment thickness.…”

Section: ) Small-scale Topographymentioning

confidence: 99%

“…They are created at midocean ridge spreading centers by faulting and volcanism, and are modified in time by sedimentation. They exhibit characteristic scales from 50 to 300 m in height, 2 to 8 km in width, and 10 to 25 km in length and obey fractal scaling below a corner wavenumber (Goff andJordan 1988, 1989;Goff et al 1997); see Fig. 2b.…”

Section: ) Small-scale Topographymentioning

confidence: 99%

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The Impact of Small-Scale Topography on the Dynamical Balance of the Ocean

Garabato

Nurser

Scott

et al. 2013

Journal of Physical Oceanography

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The impact of small-scale topography on the ocean's dynamical balance is investigated by quantifying the rates at which internal wave drag extracts (angular) momentum and vorticity from the general circulation. The calculation exploits the recent advent of two near-global descriptions of topographic roughness on horizontal scales on the order of 1-10 km, which play a central role in the generation of internal lee waves by geostrophic flows impinging on topography and have been hitherto unresolved by bathymetric datasets and ocean general circulation models alike. It is found that, while internal wave drag is a minor contributor to the ocean's dynamical balance over much of the globe, it is a significant player in the dynamics of extensive areas of the ocean, most notably the Antarctic Circumpolar Current and several regions of enhanced small-scale topographic variance in the equatorial and Southern Hemisphere oceans. There, the contribution of internal wave drag to the ocean's (angular) momentum and vorticity balances is generally on the order of ten to a few tens of percent of the dominant source and sink terms in each dynamical budget, which are respectively associated with wind forcing and form drag by topography with horizontal scales from 500 to 1000 km. It is thus suggested that the representation of internal wave drag in general circulation models may lead to significant changes in the deep ocean circulation of those regions. A theoretical scaling is derived that captures the basic dependence of internal wave drag on topographic roughness and near-bottom flow speed for most oceanographically relevant regimes.

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“…If the topographic height has a root mean square value of order 200 m, typical of abyssal hills (Goff 2010), then η −1 rms is less than 2 days. Thus even rather small topographic features produce a topographic PV with a time scale that is much less than that of the typical drag coefficient in table 2.…”

Section: The Topographymentioning

confidence: 99%

Beta-plane turbulence above monoscale topography

Constantinou

Young

2017

J. Fluid Mech.

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Using a one-layer quasi-geostrophic model, we study the effect of random monoscale topography on forced beta-plane turbulence. The forcing is a uniform steady wind stress that produces both a uniform large-scale zonal flow U (t) and smaller-scale macroturbulence characterized by both standing and transient eddies. The large-scale flow U is retarded by a combination of Ekman drag and the domain-averaged topographic form stress produced by the eddies. The topographic form stress typically balances most of the applied wind stress, while the Ekman drag provides all of the energy dissipation required to balance the wind work. A collection of statistically equilibrated numerical solutions delineates the main flow regimes and the dependence of the time-average of U on parameters such as the planetary vorticity gradient β and the statistical properties of the topography. We obtain asymptotic scaling laws for the strength of the large-scale flow U in the limiting cases of weak and strong forcing.If β is significantly smaller than the topographic PV gradient then the flow consists of stagnant pools attached to pockets of closed geostrophic contours. The stagnant dead zones are bordered by jets and the flow through the domain is concentrated into a narrow channel of open geostrophic contours. In most of the domain the flow is weak and thus the large-scale flow U is an unoccupied mean.If β is comparable to, or larger than, the topographic PV gradient then all geostrophic contours are open and the flow is uniformly distributed throughout the domain. In this open-contour case there is an "eddy saturation" regime in which U is insensitive to large changes in the wind stress. We show that eddy saturation requires strong transient eddies that act effectively as PV diffusion. This PV diffusion does not alter the kinetic energy of the standing eddies, but it does increase the topographic form stress by enhancing the correlation between topographic slope and the standing-eddy pressure field. Using bounds based on the energy and enstrophy power integrals we show that as the strength of the wind stress increases the flow transitions from a regime in which most of the form stress balances the wind stress to a regime in which the form stress is very small and large transport ensues.

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Global prediction of abyssal hill root‐mean‐square heights from small‐scale altimetric gravity variability

Cited by 50 publications

References 45 publications

Internal lee wave closures: Parameter sensitivity and comparison to observations

Internal lee wave closures: Parameter sensitivity and comparison to observations

The Impact of Small-Scale Topography on the Dynamical Balance of the Ocean

Beta-plane turbulence above monoscale topography

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