Global rate and spectral characteristics of internal gravity wave generation by geostrophic flow over topography

Abstract

[1] The rate of generation of internal gravity waves in the lee of small length scale topography by geostrophic flow in the World Ocean was estimated using linear theory with corrections for finite amplitude topography. Several global data sets were combined for the calculation including an ocean circulation model for the near-bottom geostrophic flow statistics, over 500 abyssal current meter records, historical climatological data for the buoyancy frequency, and two independent estimates of the small scale topographic statistical properties. The first topography estimate was based on an empirically-derived relationship between paleo-spreading rates and abyssal hill roughness, with corrections for sedimentation. The second estimate was based on small-scale (<100 km) roughness of satellite altimetry-derived gravity field, using upward continuation relationships to derive estimates of abyssal hill roughness at the seafloor at scales less than approximately 20 km. The lee wave generation rate was found to be between 0.34 to 0.49 TW. The Southern Hemisphere produced 92% of the lee wave energy, with the Southern Ocean dominating. Strength of the bottom flow was the most important factor in producing the global pattern of generation rate, except in the Indian Ocean where extremely rough topography produced strong lee wave generation despite only moderate bottom flows. The results imply about one half of the mechanical power input to the ocean general circulation from the extra-equatorial wind stress of the World Ocean results from abyssal lee wave generation. Topographic length scales between 176 m and 2.5 km (horizontal wavelengths between 1 and 16 km) accounted for 90% of the globally integrated generation.Citation: Scott, R. B., J. A. Goff, A. C. Naveira Garabato, and A. J. G. Nurser (2011), Global rate and spectral characteristics of internal gravity wave generation by geostrophic flow over topography,

Eddy-induced variability in Southern Ocean abyssal mixing on climatic timescales

“…Mat.). The energization of first-baroclinic mode eddy flows is a predicted effect of baroclinic instability 33 , and may be expected to enhance abyssal dissipation through the promotion of internal wave generation by intensified near-bottom eddy flow 15,17,19,20,22 and of internal wave breaking through critical layer interactions 31 .…”

“…The radiation and breaking of lee waves is estimated to account for the bulk of the dissipation of the Southern Ocean eddy field 21,22 , and to support a major fraction of the diabatic water mass transformation closing the lower overturning cell in the abyssal ocean 23 . This prompts the hypothesis that Southern Ocean abyssal mixing and overturning are sensitive to the intensity of the regional eddy field and, since the eddy field is primarily energised by instabilities of the windforced circulation 8,24,25 , to climatic perturbations in atmospheric forcing.…”

Suppression of Internal Wave Breaking in the Antarctic Circumpolar Current near Topography

“…In brief, the SOFine field campaign was situated on the northern flank of the Kerguelen Plateau in the south Indian Ocean, a region where two main jets of the ACC form large standing meanders in climatological atlases and ocean circulation models alike (Sparrow et al 1996;Sokolov and Rintoul 2009). It is also a region of complex topography expected to host elevated levels of internal wave activity and turbulence as strong near-bottom flows impinge on the roughness of the plateau slopes (e.g., Nikurashin and Ferrari 2011;Scott et al 2011;. The SOFine survey, observations from which are considered here, was conducted in November and December 2008 and consisted of a double box survey defined by three sections emanating from the Kerguelen Plateau closed by a land boundary (Kerguelen Island) to the south and a perpendicular transect to the north of the plateau slopes ( Fig.…”

Energetics of the Global Ocean: The Role of Mesoscale Eddies

“…Duhaut and Straub 2006;Greatbatch 2006, 2007;Greatbatch et al 2007;Shuchburgh et al 2011), generation of lee waves over rough topography (e.g. Marshall and Naveira Garabato 2008;Nikurashin and Ferrari 2011;Scott et al 2011), the "Neptune effect" along sloping topography (e.g. Holloway 1992; Dukowicz and Greatbatch 1999;Greatbatch and Li 2000;Adcock and Marshall 2000), and interactions with the internal wave field through loss of balance and Rossby wave deformation (e.g.…”