Global trends in surface eddy mixing from satellite altimetry

Zhang, Guangchuang; Chen, Ru; Li, Laifang; Wei, Hao; Sun, Shantong

doi:10.3389/fmars.2023.1157049

Cited by 3 publications

(4 citation statements)

References 87 publications

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“…With the focus on the 5-year means, we are assuming a slowlyvarying eddy field and attempting to parameterize its time-mean impact. However, we note that geostrophic turbulence is known to be intermittent with implications for variability in eddy transport and mixing (Busecke & Abernathey, 2019;Huneke et al, 2019;G. Zhang et al, 2023;Ong et al, 2023).…”

Section: Model Setupmentioning

confidence: 69%

Parameterizing mesoscale eddy buoyancy transport over sloping topography

Nummelin,

Isachsen

2024

Preprint

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Most of the ocean’s kinetic energy is contained within the mesoscale eddy field. Models that do not resolve these eddies tend to parameterize their impacts such that the parameterized transport of buoyancy and tracers reduces the large-scale available potential energy and spreads tracers. However, the parameterizations used in the ocean components of current generation Earth System Models (ESMs) rely on an assumption of a flat ocean floor even though observations and high-resolution modelling show that eddy transport is sensitive to the potential vorticity gradients associated with a sloping seafloor. We show that buoyancy transport coefficient diagnosed from idealized eddy-resolving simulations is indeed reduced over both prograde and retrograde bottom slopes (topographic wave propagation along or against the mean flow, respectively) and that the reduction can be skilfully captured by a mixing length parameterization by introducing the topographic Rhines scale as a length scale. This modified ‘GM’ parameterization enhances the strength of thermal wind currents over the slopes in coarse-resolution, non-eddying, simulations. We find that in realistic global coarse-resolution simulations the impact of topography is most pronounced at high latitudes, enhancing the mean flow strength and reducing temperature and salinity biases. Reducing the buoyancy transport coefficient further with a mean-flow dependent eddy efficiency factor, has notable effects also at lower latitudes and leads to reduction of global mean biases.

show abstract

Section: Model Setupmentioning

confidence: 69%

Parameterizing mesoscale eddy buoyancy transport over sloping topography

Nummelin,

Isachsen

2024

Preprint

View full text Add to dashboard Cite

show abstract

Section: Model Setupmentioning

confidence: 69%

Parameterizing mesoscale eddy buoyancy transport over sloping topography

Nummelin

Isachsen

2023

Preprint

View full text Add to dashboard Cite

Most of the ocean’s kinetic energy is contained within the mesoscale eddy field. Models that do not resolve these eddies tend to parameterize their impacts through down-gradient transport of buoyancy and tracers, aiming to reduce the large-scale available potential energy and spread tracers. However, the parameterizations used in the ocean components of current generation Earth System Models (ESMs) rely on an assumption of a flat ocean floor even though observations and high-resolution modelling show that eddy transport is sensitive to the potential vorticity gradients associated with a sloping sea floor. We show that buoyancy diffusivity diagnosed from idealized eddy-resolving simulations is indeed reduced over both prograde and retrograde bottom slopes (topographic wave propagation along or against the mean flow, respectively) and that the reduction can be skilfully captured by mixing length parameterization by introducing the topographic Rhines scale as a length scale. This modified ‘GM’ parameterization enhances the strength of thermal wind currents over the slopes in coarse-resolution, non-eddying, simulations. We find that in realistic global coarse-resolution simulations the impact of topography is most pronounced at high latitudes, enhancing the mean flow strength and reducing temperature and salinity biases. Reducing buoyancy diffusivities further with a mean-flow dependent eddy efficiency factor has notable effects also at lower latitudes and leads to reduction of global mean biases.

show abstract

“…With the focus on the 5‐year means, we are assuming a slowly‐varying eddy field and attempting to parameterize its time‐mean impact. However, we note that geostrophic turbulence is known to be intermittent with implications for variability in eddy transport and mixing (Busecke & Abernathey, 2019; Huneke et al., 2019; Ong et al., 2023; G. Zhang et al., 2023). Also our simulations suggest that over the northern prograde slope the jet there undergoes periods of alternating strong and weak eddy activity on a timescale of several months (not shown).…”

Section: Methodsmentioning

confidence: 77%

“…With the focus on the 5-year means, we are assuming a slowly-varying eddy field and attempting to parameterize its time-mean impact. However, we note that geostrophic turbulence is known to be intermittent with implications for variability in eddy transport and mixing (Busecke & Abernathey, 2019;Huneke et al, 2019;Ong et al, 2023;G. Zhang et al, 2023).…”

Section: Model Setupmentioning

confidence: 86%

Parameterizing Mesoscale Eddy Buoyancy Transport Over Sloping Topography

Nummelin,

Isachsen

2024

J Adv Model Earth Syst

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Most of the ocean's kinetic energy is contained within the mesoscale eddy field. Models that do not resolve these eddies tend to parameterize their impacts such that the parameterized transport of buoyancy and tracers reduces the large‐scale available potential energy and spreads tracers. However, the parameterizations used in the ocean components of current generation Earth System Models rely on an assumption of a flat ocean floor even though observations and high‐resolution modeling show that eddy transport is sensitive to the potential vorticity gradients associated with a sloping seafloor. We show that buoyancy transport coefficient diagnosed from idealized eddy‐resolving simulations is indeed reduced over both prograde and retrograde bottom slopes (topographic wave propagation along or against the mean flow, respectively) and that the reduction can be skilfully captured by a mixing length parameterization by introducing the topographic Rhines scale as a length scale. This modified “GM” parameterization enhances the strength of thermal wind currents over the slopes in coarse‐resolution, non‐eddying, simulations. We find that in realistic global coarse‐resolution simulations the impact of topography is most pronounced at high latitudes, enhancing the mean flow strength and reducing temperature and salinity biases. Reducing the buoyancy transport coefficient further with a mean‐flow dependent eddy efficiency factor, has notable effects also at lower latitudes and leads to reduction of global mean biases.

show abstract

Global trends in surface eddy mixing from satellite altimetry

Cited by 3 publications

References 87 publications

Parameterizing mesoscale eddy buoyancy transport over sloping topography

Parameterizing mesoscale eddy buoyancy transport over sloping topography

Parameterizing mesoscale eddy buoyancy transport over sloping topography

Parameterizing Mesoscale Eddy Buoyancy Transport Over Sloping Topography

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