Impact of topographic internal lee wave drag on an eddying global ocean model

AbstractThe effects of a parameterized linear internal wave drag on the semidiurnal barotropic and baroclinic energetics of a realistically forced, three-dimensional global ocean model are analyzed. Although the main purpose of the parameterization is to improve the surface tides, it also influences the internal tides. The relatively coarse resolution of the model of ~8 km only permits the generation and propagation of the first three vertical modes. Hence, this wave drag parameterization represents the energy conversion to and the subsequent breaking of the unresolved high modes. The total tidal energy input and the spatial distribution of the barotropic energy loss agree with the Ocean Topography Experiment (TOPEX)/Poseidon (TPXO) tidal inversion model. The wave drag overestimates the high-mode conversion at ocean ridges as measured against regional high-resolution models. The wave drag also damps the low-mode internal tides as they propagate away from their generation sites. Hence, it can be considered a scattering parameterization, causing more than 50% of the deep-water dissipation of the internal tides. In the near field, most of the baroclinic dissipation is attributed to viscous and numerical dissipation. The far-field decay of the simulated internal tides is in agreement with satellite altimetry and falls within the broad range of Argo-inferred dissipation rates. In the simulation, about 12% of the semidiurnal internal tide energy generated in deep water reaches the continental margins.

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The impact of lee waves on the Southern Ocean circulation

Journal of Physical Oceanography ◽

10.1175/jpo-d-20-0263.1 ◽

2021 ◽

Author(s):

Luwei Yang ◽

Maxim Nikurashin ◽

Andrew McC. Hogg ◽

Bernadette M. Sloyan

Keyword(s):

Southern Ocean ◽

Ocean Circulation ◽

Turbulent Mixing ◽

Wave Drag ◽

Global Ocean ◽

Mixing Effects ◽

Lee Waves ◽

Lee Wave ◽

Eddy Field ◽

The Impact

AbstractLee waves play an important role in transferring energy from the geostrophic eddy field to turbulent mixing in the Southern Ocean. As such, lee waves can impact the Southern Ocean circulation and modulate its response to changing climate through their regulation on the eddy field and turbulent mixing. The drag effect of lee waves on the eddy field and the mixing effect of lee waves on the tracer field have been studied separately to show their importance. However, it remains unclear how the drag and mixing effects act together to modify the Southern Ocean circulation. In this study, a lee wave parameterization that includes both lee wave drag and its associated lee-wave-driven mixing is developed and implemented in an eddy-resolving idealized model of the Southern Ocean to simulate and quantify the impacts of lee waves on the Southern Ocean circulation. The results show that lee waves enhance the baroclinic transport of the Antarctic Circumpolar Current (ACC) and strengthen the lower overturning circulation. The impact of lee waves on the large-scale circulation are explained by the control of lee wave drag on isopycnal slopes through their effect on eddies, and by the control of lee-wave-driven mixing on deep stratification and water mass transformation. The results also show that the drag and mixing effects are coupled such that they act to weaken one another. The implication is that the future parameterization of lee waves in global ocean and climate models should take both drag and mixing effects into consideration for a more accurate representation of their impact on the ocean circulation.

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A closure for lee wave drag on the large-scale ocean circulation

Journal of Physical Oceanography ◽

10.1175/jpo-d-20-0230.1 ◽

2021 ◽

Author(s):

Carsten Eden ◽

Dirk Olbers ◽

Thomas Eriksen

Keyword(s):

Large Scale ◽

Surface Wind ◽

Wave Drag ◽

Ocean Model ◽

Mean Flow ◽

Model Simulations ◽

Energy Transfers ◽

Lee Waves ◽

Lee Wave ◽

The Mean

AbstractA new, energetically and dynamically consistent closure for the lee wave drag on the large scale circulation is developed and tested in idealized and realistic ocean model simulations. The closure is based on the radiative transfer equation for internal gravity waves, integrated over wavenumber space, and consists of two lee wave energy compartments for up-and downward propagating waves, which can be co-integrated in an ocean model. Mean parameters for vertical propagation, mean-ow interaction, and the vertical wave momentum flux are calculated assuming that the lee waves stay close to the spectral shape given by linear theory of their generation.Idealized model simulations demonstrate how lee waves are generated and interact with the mean flow and contribute to mixing, and document parameter sensitivities. A realistic eddy-permitting global model at 1/10° resolution coupled to the new closure yields a globally integrated energy flux of 0.27 TW into the lee wave field. The bottom lee wave stress on the mean flow can be locally as large as the surface wind stress and can reach into the surface layer. The interior energy transfers by the stress are directed from the mean flow to the waves, but this often reverses, for example in the Southern Ocean in case of shear reversal close to the bottom. The global integral of the interior energy transfers from mean ow to waves is 0.14 TW, while 0.04 TW is driving the mean ow, but this share depends on parameter choices for non-linear effects.

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The Global Ocean Forecast System, Version 3.0 (GOFS 3.0) or the Hybrid Coordinate Ocean Model (HYCOM)

10.21236/ada570050 ◽

2012 ◽

Author(s):

Frank L. Bub

Keyword(s):

Ocean Model ◽

Global Ocean ◽

Forecast System ◽

Hybrid Coordinate Ocean Model

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Response to Filchner-Ronne Ice Shelf cavity warming in a coupled ocean–ice sheet model. Part I: The ocean perspective

10.5194/os-2017-41 ◽

2017 ◽

Cited By ~ 1

Author(s):

Ralph Timmermann ◽

Sebastian Goeller

Keyword(s):

World Ocean ◽

Ice Sheet ◽

Coupled Model ◽

Freezing Temperature ◽

Ocean Model ◽

Climate Forcing ◽

Global Ocean ◽

Ice Shelf ◽

Marginal Seas ◽

Grounding Line

Abstract. A Regional Antarctic and Global Ocean (RAnGO) model has been developed to study the interaction between the world ocean and the Antarctic ice sheet. The coupled model is based on a global implementation of the Finite Element Sea-ice Ocean Model (FESOM) with a mesh refinement in the Southern Ocean, particularly in its marginal seas and in the sub-ice shelf cavities. The cryosphere is represented by a regional setup of the ice flow model RIMBAY comprising the Filchner-Ronne Ice Shelf and the grounded ice in its catchment area up to the ice divides. At the base of the RIMBAY ice shelf, melt rates from FESOM's ice-shelf component are supplied. RIMBAY returns ice thickness and the position of the grounding line. The ocean model uses a pre-computed mesh to allow for an easy adjustment of the model domain to a varying cavity geometry. RAnGO simulations with a 20th-century climate forcing yield realistic basal melt rates and a quasi-stable grounding line position close to the presently observed state. In a centennial-scale warm-water-inflow scenario, the model suggests a substantial thinning of the ice shelf and a local retreat of the grounding line. The potentially negative feedback from ice-shelf thinning through a rising in-situ freezing temperature is more than outweighed by the increasing water column thickness in the deepest parts of the cavity. Compared to a control simulation with fixed ice-shelf geometry, the coupled model thus yields a slightly stronger increase of ice-shelf basal melt rates.

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Antarctic ice sheet fertilises the Southern Ocean

Biogeosciences ◽

10.5194/bg-11-2635-2014 ◽

2014 ◽

Vol 11 (10) ◽

pp. 2635-2643 ◽

Cited By ~ 53

Author(s):

R. Death ◽

J. L. Wadham ◽

F. Monteiro ◽

A. M. Le Brocq ◽

M. Tranter ◽

...

Keyword(s):

Southern Ocean ◽

Ice Sheet ◽

Ocean Model ◽

Coastal Sediments ◽

Global Ocean ◽

Iron Cycling ◽

Antarctic Ice Sheet ◽

Significant Control ◽

Subglacial Meltwater ◽

The Impact

Abstract. Southern Ocean (SO) marine primary productivity (PP) is strongly influenced by the availability of iron in surface waters, which is thought to exert a significant control upon atmospheric CO2 concentrations on glacial/interglacial timescales. The zone bordering the Antarctic Ice Sheet exhibits high PP and seasonal plankton blooms in response to light and variations in iron availability. The sources of iron stimulating elevated SO PP are in debate. Established contributors include dust, coastal sediments/upwelling, icebergs and sea ice. Subglacial meltwater exported at the ice margin is a more recent suggestion, arising from intense iron cycling beneath the ice sheet. Icebergs and subglacial meltwater may supply a large amount of bioavailable iron to the SO, estimated in this study at 0.07–0.2 Tg yr−1. Here we apply the MIT global ocean model (Follows et al., 2007) to determine the potential impact of this level of iron export from the ice sheet upon SO PP. The export of iron from the ice sheet raises modelled SO PP by up to 40%, and provides one plausible explanation for seasonally very high in situ measurements of PP in the near-coastal zone. The impact on SO PP is greatest in coastal regions, which are also areas of high measured marine PP. These results suggest that the export of Antarctic runoff and icebergs may have an important impact on SO PP and should be included in future biogeochemical modelling.

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M2 tidal dynamics in the Ross Sea

Antarctic Science ◽

10.1017/s0954102003001044 ◽

2003 ◽

Vol 15 (1) ◽

pp. 41-46 ◽

Cited By ~ 13

Author(s):

ROBIN ROBERTSON ◽

AIKE BECKMANN ◽

HARTMUT HELLMER

Keyword(s):

Continental Shelf ◽

Ross Sea ◽

Tidal Energy ◽

Ocean Model ◽

Internal Tides ◽

Global Ocean ◽

Tidal Dynamics ◽

Tidal Elevation ◽

Shelf Slope ◽

Continental Shelf Slope

In certain regions of the Southern Ocean, tidal energy is believed to foster the mixing of different water masses, which eventually contribute to the formation of deep and bottom waters. The Ross Sea is one of the major ventilation sites of the global ocean abyss and a region of sparse tidal observations. We investigated M2 tidal dynamics in the Ross Sea using a three-dimensional sigma coordinate model, the Regional Ocean Model System (ROMS). Realistic topography and hydrography from existing observational data were used with a single tidal constituent, the semi-diurnal M2. The model fields faithfully reproduced the major features of the tidal circulation and had reasonable agreement with ten existing tidal elevation observations and forty-two existing tidal current measurements. The differences were attributed primarily to topographic errors. Internal tides were generated at the continental shelf/slope break and other areas of steep topography. Strong vertical shears in the horizontal velocities occurred under and at the edges of the Ross Ice Shelf and along the continental shelf/slope break. Estimates of lead formation based on divergence of baroclinic velocities were significantly higher than those based on barotrophic velocities, reaching over 10% at the continental shelf/slope break.

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Experimental and diagnostic protocol for the physical component of the CMIP6 Ocean Model Intercomparison Project (OMIP)

10.5194/gmd-2016-77 ◽

2016 ◽

Cited By ~ 4

Author(s):

Stephen M. Griffies ◽

Gokhan Danabasoglu ◽

Paul J. Durack ◽

Alistair J. Adcroft ◽

V. Balaji ◽

...

Keyword(s):

Sea Ice ◽

Global Climate ◽

Coupled Model ◽

Companion Paper ◽

Ocean Model ◽

Global Ocean ◽

Model Intercomparison ◽

Experimental Protocol ◽

Diagnostic Protocol ◽

Intercomparison Project

Abstract. The Ocean Model Intercomparison Project (OMIP) aims to provide a framework for evaluating, understanding, and improving the ocean and sea-ice components of global climate and earth system models contributing to the Coupled Model Intercomparison Project Phase 6 (CMIP6). OMIP addresses these aims in two complementary manners: (A) by providing an experimental protocol for global ocean/sea-ice models run with a prescribed atmospheric forcing, (B) by providing a protocol for ocean diagnostics to be saved as part of CMIP6. We focus here on the physical component of OMIP, with a companion paper (Orr et al., 2016) offering details for the inert chemistry and interactive biogeochemistry. The physical portion of the OMIP experimental protocol follows that of the interannual Coordinated Ocean-ice Reference Experiments (CORE-II). Since 2009, CORE-I (Normal Year Forcing) and CORE-II have become the standard method to evaluate global ocean/sea-ice simulations and to examine mechanisms for forced ocean climate variability. The OMIP diagnostic protocol is relevant for any ocean model component of CMIP6, including the DECK (Diagnostic, Evaluation and Characterization of Klima experiments), historical simulations, FAFMIP (Flux Anomaly Forced MIP), C4MIP (Coupled Carbon Cycle Climate MIP), DAMIP (Detection and Attribution MIP), DCPP (Decadal Climate Prediction Project), ScenarioMIP (Scenario MIP), as well as the ocean-sea ice OMIP simulations. The bulk of this paper offers scientific rationale for saving these diagnostics.

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Antarctic Ice Sheet fertilises the Southern Ocean

Biogeosciences Discussions ◽

10.5194/bgd-10-12551-2013 ◽

2013 ◽

Vol 10 (7) ◽

pp. 12551-12570 ◽

Cited By ~ 8

Author(s):

R. Death ◽

J. L. Wadham ◽

F. Monteiro ◽

A. M. Le Brocq ◽

M. Tranter ◽

...

Keyword(s):

Southern Ocean ◽

Ice Sheet ◽

Ocean Model ◽

Coastal Sediments ◽

Global Ocean ◽

Iron Cycling ◽

Antarctic Ice Sheet ◽

Significant Control ◽

Subglacial Meltwater ◽

The Impact

Abstract. Southern Ocean (SO) marine primary productivity (PP) is strongly influenced by the availability of iron in surface waters, which is thought to exert a significant control upon atmospheric CO2 concentrations on glacial/interglacial timescales. The zone bordering the Antarctic Ice Sheet exhibits high PP and seasonal plankton blooms in response to light and variations in iron availability. The sources of iron stimulating elevated SO PP are in debate. Established contributors include dust, coastal sediments/upwelling, icebergs and sea ice. Subglacial meltwater exported at the ice margin is a more recent suggestion, arising from intense iron cycling beneath the ice sheet. Icebergs and subglacial meltwater may supply a large amount of bioavailable iron to the SO, estimated in this study at 0.07–1.0 Tg yr−1. Here we apply the MIT global ocean model (Follows et al., 2007) to determine the potential impact of this level of iron export from the ice sheet upon SO PP. The export of iron from the ice sheet raises modelled SO PP by up to 40%, and provides one plausible explanation for very high seasonally observed PP in the near-coastal zone. The impact on SO PP is greatest in coastal regions, which are also areas of high observed marine PP. These results suggest that the export of Antarctic runoff and icebergs may have an important impact on SO PP and should be included in future biogeochemical modelling.

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