Toward an internal gravity wave spectrum in global ocean models

Office of Naval Research, National Science FoundationPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/111824/1/grl_internalwavespectrum_2015.pd

Skill tests of three-dimensional tidal currents in a global ocean model: A look at the North Atlantic

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/92458/1/jgr_timkoetal_northatlatnictidalcurrentskilltest_2012.pd

On eddy viscosity, energy cascades, and the horizontal resolution of gridded satellite altimeter products

Author Posting. © American Meteorological Society, 2013. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 43 (2013): 283–300, doi:10.1175/JPO-D-11-0240.1.Motivated by the recent interest in ocean energetics, the widespread use of horizontal eddy viscosity in models, and the promise of high horizontal resolution data from the planned wide-swath satellite altimeter, this paper explores the impacts of horizontal eddy viscosity and horizontal grid resolution on geostrophic turbulence, with a particular focus on spectral kinetic energy fluxes Π(K) computed in the isotropic wavenumber (K) domain. The paper utilizes idealized two-layer quasigeostrophic (QG) models, realistic high-resolution ocean general circulation models, and present-generation gridded satellite altimeter data. Adding horizontal eddy viscosity to the QG model results in a forward cascade at smaller scales, in apparent agreement with results from present-generation altimetry. Eddy viscosity is taken to roughly represent coupling of mesoscale eddies to internal waves or to submesoscale eddies. Filtering the output of either the QG or realistic models before computing Π(K) also greatly increases the forward cascade. Such filtering mimics the smoothing inherent in the construction of present-generation gridded altimeter data. It is therefore difficult to say whether the forward cascades seen in present-generation altimeter data are due to real physics (represented here by eddy viscosity) or to insufficient horizontal resolution. The inverse cascade at larger scales remains in the models even after filtering, suggesting that its existence in the models and in altimeter data is robust. However, the magnitude of the inverse cascade is affected by filtering, suggesting that the wide-swath altimeter will allow a more accurate determination of the inverse cascade at larger scales as well as providing important constraints on smaller-scale dynamics.BKA received support from Office of Naval Research Grant N00014-11-1-0487, National Science Foundation (NSF) Grants OCE-0924481 and OCE- 09607820, and University of Michigan startup funds. KLP acknowledges support from Woods Hole Oceanographic Institution bridge support funds. RBS acknowledges support from NSF grants OCE-0960834 and OCE-0851457, a contract with the National Oceanography Centre, Southampton, and a NASA subcontract to Boston University. JFS and JGR were supported by the projects ‘‘Global and remote littoral forcing in global ocean models’’ and ‘‘Agesotrophic vorticity dynamics of the ocean,’’ respectively, both sponsored by the Office of Naval Research under program element 601153N.2013-08-0

Bottom dissipation of subinertial currents at the Atlantic zonal boundaries

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90515/1/jgr_bbldiss_wrightetal_2012.pd

Improved Internal Wave Spectral Continuum in a Regional Ocean Model

Recent work demonstrates that high‐resolution global models forced simultaneously by atmospheric fields and the astronomical tidal potential contain a partial internal (gravity) wave (IW) spectral continuum. Regional simulations of the MITgcm forced at the horizontal boundaries by a global run that carries a partial IW continuum spectrum are performed at the same grid spacing as the global run and at finer grid spacings in an attempt to fill out more of the IW spectral continuum. Decreasing only the horizontal grid spacing from 2 to 0.25 km greatly improves the frequency spectra and slightly improves the vertical wavenumber spectra of the horizontal velocity. Decreasing only the vertical grid spacing by a factor of 3 does not yield any significant improvements. Decreasing both horizontal and vertical grid spacings yields the greatest degree of improvement, filling the frequency spectrum out to 72 cpd. Our results suggest that improved IW spectra in regional models are possible if they are run at finer grid spacings and are forced at their lateral boundaries by remotely generated IWs. Additionally, consistency relations demonstrate that improvements in the spectra are indeed due to the existence of IWs at higher frequencies and vertical wavenumbers when remote IW forcing is included and model grid spacings decrease. By being able to simulate an IW spectral continuum to 0.25 km scales, these simulations demonstrate that one may be able to track the energy pathways of IWs from generation to dissipation and improve the understanding of processes such as IW‐driven mixing.Plain Language SummaryModels of internal waves (IWs) may help us to better understand the spatial geography of mixing in the ocean and are playing an increasingly important role in the planning of satellite missions. Following recent work showing that high‐resolution global models contain a partial IW spectrum, this paper describes further improvements in the spectrum seen in a high‐resolution regional model forced at the boundaries by a previously performed global IW simulation. Decreasing only the horizontal grid spacing greatly improves the frequency spectra and slightly improves the vertical wavenumber spectra of velocity. Increasing only the number of vertical levels does not yield any significant improvements. Decreasing both horizontal and vertical grid spacings yields the greatest improvement in both spectra. Our results suggest that regional models can exhibit improved IW spectra over global models if two conditions are met—they must have higher horizontal and vertical resolutions, and they must have remotely generated IWs at their boundaries. Application of the so‐called consistency relations demonstrates that the model is indeed carrying a field of high‐frequency IWs. Being able to simulate a fuller IW spectrum demonstrates that one may be able to use these models to improve the understanding of IW‐driven processes and energy pathways.Key PointsInternal gravity wave spectra in regional models are more realistic as model grid spacing decreasesThe vertical wavenumber spectra improve less dramatically than the frequency spectraInternal gravity wave consistency relations are applied to modeled spectraPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154917/1/jgrc23947_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154917/2/jgrc23947.pd

Effects of stencil width on surface ocean geostrophic velocity and vorticity estimation from gridded satellite altimeter data

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90421/1/2011JC007367.pd

Effects of stencil width on surface ocean geostrophic velocity and vorticity estimation from gridded satellite altimeter data

This paper examines the effect of “stencil width” on surface ocean geostrophic velocity and vorticity estimated from differentiating gridded satellite altimeter sea surface height products. In oceanographic applications, the value of the first derivative at a central grid point is generally obtained by differencing the sea surface heights at adjacent grid points. This is called a “three-point stencil centered difference”. Here the stencil width is increased from three to five, seven, and nine points, using well-known formulae from the numerical analysis literature. The discrepancies between velocities computed with successive stencils decreases with increasing stencil width, suggesting that wide stencil results are more reliable. Significant speed-dependent biases (up to 10–20%) are found between results computed from three-point stencils versus those computed from wider stencils. The geostrophic velocity, and the variance of geostrophic velocity, are underestimated with thin stencils. Similar results are seen in geostrophic velocities computed from high-resolution model output. In contrast to the case when three-point stencils are used, wider stencils yield estimates of the anisotropy of velocity variance that are insensitive to the differences in grid spacing between two widely used altimeter products. Three-point stencils yield incorrect anisotropies on the 1/4° anisotropic AVISO grid; we recommend the use of 7-point stencils. Despite the demonstrated inadequacies of the three-point stencils, the conclusions of earlier studies based on them, that the zonally averaged midlatitude eddy kinetic energy field is nearly isotropic, are found to pertain also with wider stencils. Finally, the paper also examines the strengths and limitations of applying noise-suppressing differentiators, versus classic centered differences, to altimeter data

An evaluation of the barotropic and internal tides in a high-resolution global ocean circulation model

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94189/1/jgr_shriveretal_hycomaltimetrytidecomparison_2012.pd

Three-party entanglement from positronium

The decay of ortho-positronium into three photons produces a physical realization of a pure state with three-party entanglement. Its quantum correlations are analyzed using recent results on quantum information theory, looking for the final state which has the maximal amount of GHZ-like correlations. This state allows for a statistical dismissal of local realism stronger than the one obtained using any entangled state of two spin one-half particles.Comment: REVTEX, 13 pages, 3 figure

Long-term Earth-Moon evolution with high-level orbit and ocean tide models

Tides and Earth‐Moon system evolution are coupled over geological time. Tidal energy dissipation on Earth slows [Formula: see text] rotation rate, increases obliquity, lunar orbit semi‐major axis and eccentricity, and decreases lunar inclination. Tidal and core‐mantle boundary dissipation within the Moon decrease inclination, eccentricity and semi‐major axis. Here we integrate the Earth‐Moon system backwards for 4.5 Ga with orbital dynamics and explicit ocean tide models that are “high‐level” (i.e., not idealized). To account for uncertain plate tectonic histories, we employ Monte Carlo simulations, with tidal energy dissipation rates (normalized relative to astronomical forcing parameters) randomly selected from ocean tide simulations with modern ocean basin geometry and with 55, 116, and 252 Ma reconstructed basin paleogeometries. The normalized dissipation rates depend upon basin geometry and [Formula: see text] rotation rate. Faster Earth rotation generally yields lower normalized dissipation rates. The Monte Carlo results provide a spread of possible early values for the Earth‐Moon system parameters. Of consequence for ocean circulation and climate, absolute (un‐normalized) ocean tidal energy dissipation rates on the early Earth may have exceeded [Formula: see text] rate due to a closer Moon. Prior to [Formula: see text] , evolution of inclination and eccentricity is dominated by tidal and core‐mantle boundary dissipation within the Moon, which yield high lunar orbit inclinations in the early Earth‐Moon system. A drawback for our results is that the semi‐major axis does not collapse to near‐zero values at 4.5 Ga, as indicated by most lunar formation models. Additional processes, missing from our current efforts, are discussed as topics for future investigation