Simulation of the Arctic – North Atlantic Ocean Circulation with a Two-Equation k-omega Turbulence Parameterization

A method for solving the turbulence equations embedded in the sigma ocean general ocean circulation model is proposed. Like the general circulation model, the turbulence equations are solved using the splitting method by physical processes. The turbulence equations are split into two main stages describing transport-diffusion and generation-dissipation processes. Parameterization of turbulence in the framework of equations allows, at the generation-dissipation stage, to use both numerical and analytical solutions and to ensure high efficiency of the algorithm. The results of large-scale ocean dynamics simulation taking into account the parameterization of vertical turbulent exchange are considered. Numerical experiments were carried out using k-omega turbulence model embedded to the Institute of Numerical Mathematics Ocean general circulation Model (INMOM). Both the circulation and turbulence models are solved using the splitting method with respect to physical processes. The coupled model is used to simulate the hydrophysical fields of the North Atlantic and Arctic Oceans for 1948--2009. The model has a horizontal resolution of 0.25 degree and 40 sigma-levels along the vertical. The sensitivity of the solution to the changes in mixing parameterization is studied. Experiments demonstrate that taking into account the climatic annual mean buoyancy frequency improves the reproduction of large-scale ocean characteristics. There is a positive effect of Prandtl number variations for reproducing the upper mixed layer depth. The experiments also demonstrate the computational effectiveness of the proposed approach in solving the turbulence equations.

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Simulation of the Arctic—North Atlantic Ocean Circulation with a Two-Equation K-Omega Turbulence Parameterization

Journal of Marine Science and Engineering ◽

10.3390/jmse6030095 ◽

2018 ◽

Vol 6 (3) ◽

pp. 95 ◽

Cited By ~ 1

Author(s):

Sergey Moshonkin ◽

Vladimir Zalesny ◽

Anatoly Gusev

Keyword(s):

Prandtl Number ◽

Ocean Circulation ◽

North Atlantic ◽

Large Scale ◽

Mixed Layer Depth ◽

Ocean Dynamics ◽

Dynamics Simulation ◽

The Arctic ◽

Buoyancy Frequency ◽

Physical Factors

The results of large-scale ocean dynamics simulation taking into account the parameterization of vertical turbulent exchange are considered. Numerical experiments were carried out using k − ω turbulence model embedded to the Institute of Numerical Mathematics Ocean general circulation Model (INMOM). Both the circulation and turbulence models are solved using the splitting method with respect to physical processes. We split k − ω equations into the two stages describing transport-diffusion and generation-dissipation processes. At the generation-dissipation stage, the equation for ω does not depend on k. It allows us to solve both turbulence equations analytically that ensure high computational efficiency. The coupled model is used to simulate the hydrophysical fields of the North Atlantic and Arctic Oceans for 1948–2009. The model has a horizontal resolution of 0.25 ∘ and 40 σ -levels along the vertical. The numerical results show the model’s satisfactory performance in simulating large-scale ocean circulation and upper layer dynamics. The sensitivity of the solution to the change in the coefficients entering into the analytical solution of the k − ω model which describe the influence of some physical factors is studied. These factors are the climatic annual mean buoyancy frequency (AMBF) and Prandtl number as a function of the Richardson number. The experiments demonstrate that taking into account the AMBF improves the reproduction of large-scale ocean characteristics. Prandtl number variations improve the upper mixed layer depth simulation.

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Simulating oceanic radiocarbon with the FAMOUS GCM: implications for its use as a proxy for ventilation and carbon uptake

10.5194/bg-2019-365 ◽

2019 ◽

Cited By ~ 1

Author(s):

Jennifer E. Dentith ◽

Ruza F. Ivanovic ◽

Lauren J. Gregoire ◽

Julia C. Tindall ◽

Laura F. Robinson ◽

...

Keyword(s):

Carbon Cycle ◽

Ocean Circulation ◽

North Atlantic ◽

General Circulation ◽

Large Scale ◽

Circulation Model ◽

Deep Ocean ◽

Intermediate Water ◽

Water Age ◽

Surface Ocean

Abstract. Constraining ocean circulation and its temporal variability is crucial for understanding changes in surface climate and the carbon cycle. Radiocarbon (14C) is often used as a geochemical tracer of ocean circulation, but interpreting ∆14C in geological archives is complex. Isotope-enabled models enable us to directly compare simulated ∆14C values to Δ14C measurements and investigate plausible mechanisms for the observed signals. We have added three new tracers (water age, abiotic 14C, and biotic 14C) to the ocean component of the FAMOUS General Circulation Model to study large-scale ocean circulation and the marine carbon cycle. Following a 10 000 year spin-up, we prescribed the Suess effect (the isotopic imprint of anthropogenic fossil fuel burning) and the bomb pulse (the isotopic imprint of thermonuclear weapons testing) in a transient simulation spanning 1765 to 2000 CE. To validate the new isotope scheme, we compare the model output to direct ∆14C observations in the surface ocean (pre-bomb and post-bomb) and at depth (post-bomb only). We also compare the timing, shape and amplitude of the simulated marine bomb spike to ∆14C in geological archives from shallow-to-intermediate water depths across the North Atlantic. The model captures the large-scale structure and range of ∆14C values (both spatially and temporally) suggesting that, on the whole, the uptake and transport of 14C are well represented in FAMOUS. Differences between the simulated and observed values arise due to physical model biases (such as weak surface winds and over-deep North Atlantic Deep Water), demonstrating the potential of the 14C tracer as a sensitive, independent tuning diagnostic. We also examine the importance of the biological pump for deep ocean 14C concentrations and assess the extent to which 14C can be interpreted as a ventilation tracer. Comparing the simulated biotic and abiotic δ14C, we infer that biology has a spatially heterogeneous influence on 14C distributions in the surface ocean (between 18 and 30 ‰), but a near constant influence at depth (≈ 20 ‰). Nevertheless, the decoupling between the simulated water ages and the simulated 14C ages in FAMOUS demonstrates that interpreting proxy ∆14C measurements in terms of ventilation alone could lead to erroneous conclusions about palaeocean circulation. Specifically, our results suggest that ∆14C is only a faithful proxy for water age in regions with strong convection; elsewhere, the temperature dependence of the solubility of CO2 in seawater complicates the signal.

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Extreme Precipitation in an Atmosphere General Circulation Model: Impact of Horizontal and Vertical Model Resolutions

Journal of Climate ◽

10.1175/jcli-d-14-00337.1 ◽

2015 ◽

Vol 28 (3) ◽

pp. 1184-1205 ◽

Cited By ~ 18

Author(s):

Claudia Volosciuk ◽

Douglas Maraun ◽

Vladimir A. Semenov ◽

Wonsun Park

Keyword(s):

General Circulation Model ◽

Extreme Precipitation ◽

General Circulation ◽

Large Scale ◽

Circulation Model ◽

Generalized Extreme Value Distribution ◽

Precipitation Extremes ◽

Vertical Resolution ◽

Physical Processes ◽

The Impact

Abstract To investigate the influence of atmospheric model resolution on the representation of daily precipitation extremes, ensemble simulations with the atmospheric general circulation model ECHAM5 at different horizontal (from T213 to T31 spectral truncation) and vertical (from L31 to L19) resolutions and forced with observed sea surface temperatures and sea ice concentrations have been carried out for January 1982–September 2010. All results have been compared with the highest resolution, which has been validated against observations. Resolution affects both the representation of physical processes and the averaging of precipitation across grid boxes. The latter, in particular, smooths out localized extreme events. These effects have been disentangled by averaging precipitation simulated at the highest resolution to the corresponding coarser grid. Extremes are represented by seasonal maxima, modeled by the generalized extreme value distribution. Effects of averaging and representation of physical processes vary with region and season. In the tropical summer hemisphere, extreme precipitation is reduced by up to 30% due to the averaging effect, and a further 65% owing to a coarser representation of physical processes. Toward middle to high latitudes, the latter effect reduces to 20%; in the winter hemisphere it vanishes toward the poles. A strong drop is found between T106 and T63 in the convection-dominated tropics. At the lowest resolution, Northern Hemisphere winter precipitation extremes, mainly caused by large-scale weather systems, are in general represented reasonably well. Coarser vertical resolution causes an equatorward shift of maximum extreme precipitation in the tropics. The impact of vertical resolution on mean precipitation is less pronounced; for horizontal resolution it is negligible.

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Simulating stable carbon isotopes in the ocean component of the FAMOUS general circulation model with MOSES1 (XOAVI)

Geoscientific Model Development ◽

10.5194/gmd-13-3529-2020 ◽

2020 ◽

Vol 13 (8) ◽

pp. 3529-3552

Author(s):

Jennifer E. Dentith ◽

Ruza F. Ivanovic ◽

Lauren J. Gregoire ◽

Julia C. Tindall ◽

Laura F. Robinson

Keyword(s):

General Circulation Model ◽

Ocean Circulation ◽

General Circulation ◽

Large Scale ◽

Stable Carbon Isotopes ◽

Numerical Models ◽

Circulation Model ◽

Ocean General Circulation Model ◽

Fossil Fuel Burning ◽

Isotope Distributions

Abstract. Ocean circulation and the marine carbon cycle can be indirectly inferred from stable and radiogenic carbon isotope ratios (δ13C and Δ14C, respectively), measured directly in the water column, or recorded in geological archives such as sedimentary microfossils and corals. However, interpreting these records is non-trivial because they reflect a complex interplay between physical and biogeochemical processes. By directly simulating multiple isotopic tracer fields within numerical models, we can improve our understanding of the processes that control large-scale isotope distributions and interpolate the spatiotemporal gaps in both modern and palaeo datasets. We have added the stable isotope 13C to the ocean component of the FAMOUS coupled atmosphere–ocean general circulation model, which is a valuable tool for simulating complex feedbacks between different Earth system processes on decadal to multi-millennial timescales. We tested three different biological fractionation parameterisations to account for the uncertainty associated with equilibrium fractionation during photosynthesis and used sensitivity experiments to quantify the effects of fractionation during air–sea gas exchange and primary productivity on the simulated δ13CDIC distributions. Following a 10 000-year pre-industrial spin-up, we simulated the Suess effect (the isotopic imprint of anthropogenic fossil fuel burning) to assess the performance of the model in replicating modern observations. Our implementation captures the large-scale structure and range of δ13CDIC observations in the surface ocean, but the simulated values are too high at all depths, which we infer is due to biases in the biological pump. In the first instance, the new 13C tracer will therefore be useful for recalibrating both the physical and biogeochemical components of FAMOUS.

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Simulating stable carbon isotopes in the ocean component of the FAMOUS General Circulation Model with MOSES1 (XOAVI)

10.5194/gmd-2019-250 ◽

2020 ◽

Author(s):

Jennifer E. Dentith ◽

Ruza F. Ivanovic ◽

Lauren J. Gregoire ◽

Julia C. Tindall ◽

Laura F. Robinson

Keyword(s):

General Circulation Model ◽

Ocean Circulation ◽

General Circulation ◽

Large Scale ◽

Stable Carbon Isotopes ◽

Numerical Models ◽

Circulation Model ◽

Ocean General Circulation Model ◽

Fossil Fuel Burning ◽

Isotope Distributions

Abstract. Isotopic ratios are often utilised as proxies for ocean circulation and the marine carbon cycle. However, interpreting these records is non-trivial because they reflect a complex interplay between physical and biogeochemical processes. By directly simulating multiple isotopic tracer fields within numerical models, we can improve our understanding of the processes that control large-scale isotope distributions and interpolate the spatiotemporal gaps in both modern and palaeo datasets. We have added the stable isotope 13C to the ocean component of the FAMOUS coupled atmosphere-ocean General Circulation Model, which is a valuable tool for simulating complex feedbacks between different Earth System processes on decadal to multi-millennial timescales. We tested three different biological fractionation parameterisations to account for the uncertainty associated with equilibrium fractionation during photosynthesis and used sensitivity experiments to quantify the effects of fractionation during air-sea gas exchange and primary productivity on the simulated δ13CDIC distributions. Following a 10,000 year pre-industrial spin-up, we simulated the Suess effect (the isotopic imprint of anthropogenic fossil fuel burning) to assess the performance of the model in replicating modern observations. Our implementation captures the large-scale structure and range of δ13CDIC observations in the surface ocean, but the simulated values are too high at all depths, which we infer is due to biases in the biological pump. In the first instance, the new 13C tracer will therefore be useful for recalibrating both the physical and biogeochemical components of FAMOUS.

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Asynchronous warming and δ18O evolution of deep Atlantic water masses during the last deglaciation

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1704512114 ◽

2017 ◽

Vol 114 (42) ◽

pp. 11075-11080 ◽

Cited By ~ 16

Author(s):

Jiaxu Zhang ◽

Zhengyu Liu ◽

Esther C. Brady ◽

Delia W. Oppo ◽

Peter U. Clark ◽

...

Keyword(s):

Ocean Circulation ◽

North Atlantic ◽

General Circulation ◽

Large Scale ◽

Water Mass ◽

Critical Role ◽

Circulation Model ◽

Deep Ocean ◽

Last Deglaciation ◽

The Last Deglaciation

The large-scale reorganization of deep ocean circulation in the Atlantic involving changes in North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW) played a critical role in regulating hemispheric and global climate during the last deglaciation. However, changes in the relative contributions of NADW and AABW and their properties are poorly constrained by marine records, including δ18O of benthic foraminiferal calcite (δ18Oc). Here, we use an isotope-enabled ocean general circulation model with realistic geometry and forcing conditions to simulate the deglacial water mass and δ18O evolution. Model results suggest that, in response to North Atlantic freshwater forcing during the early phase of the last deglaciation, NADW nearly collapses, while AABW mildly weakens. Rather than reflecting changes in NADW or AABW properties caused by freshwater input as suggested previously, the observed phasing difference of deep δ18Oc likely reflects early warming of the deep northern North Atlantic by ∼1.4 °C, while deep Southern Ocean temperature remains largely unchanged. We propose a thermodynamic mechanism to explain the early warming in the North Atlantic, featuring a strong middepth warming and enhanced downward heat flux via vertical mixing. Our results emphasize that the way that ocean circulation affects heat, a dynamic tracer, is considerably different from how it affects passive tracers, like δ18O, and call for caution when inferring water mass changes from δ18Oc records while assuming uniform changes in deep temperatures.

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Global Climate and Ocean Circulation on an Aquaplanet Ocean–Atmosphere General Circulation Model

Journal of Climate ◽

10.1175/jcli3874.1 ◽

2006 ◽

Vol 19 (18) ◽

pp. 4719-4737 ◽

Cited By ~ 25

Author(s):

Robin S. Smith ◽

Clotilde Dubois ◽

Jochem Marotzke

Keyword(s):

Surface Temperature ◽

General Circulation Model ◽

Ocean Circulation ◽

General Circulation ◽

Large Scale ◽

Circulation Model ◽

Zonal Flow ◽

Climate Simulation ◽

Ocean Atmosphere ◽

Atmosphere General Circulation Model

Abstract A low-resolution coupled ocean–atmosphere general circulation model (OAGCM) is used to study the characteristics of the large-scale ocean circulation and its climatic impacts in a series of global coupled aquaplanet experiments. Three configurations, designed to produce fundamentally different ocean circulation regimes, are considered. The first has no obstruction to zonal flow, the second contains a low barrier that blocks zonal flow in the ocean at all latitudes, creating a single enclosed basin, while the third contains a gap in the barrier to allow circumglobal flow at high southern latitudes. Warm greenhouse climates with a global average air surface temperature of around 27°C result in all cases. Equator-to-pole temperature gradients are shallower than that of a current climate simulation. While changes in the land configuration cause regional changes in temperature, winds, and rainfall, heat transports within the system are little affected. Inhibition of all ocean transport on the aquaplanet leads to a reduction in global mean surface temperature of 8°C, along with a sharpening of the meridional temperature gradient. This results from a reduction in global atmospheric water vapor content and an increase in tropical albedo, both of which act to reduce global surface temperatures. Fitting a simple radiative model to the atmospheric characteristics of the OAGCM solutions suggests that a simpler atmosphere model, with radiative parameters chosen a priori based on the changing surface configuration, would have produced qualitatively different results. This implies that studies with reduced complexity atmospheres need to be guided by more complex OAGCM results on a case-by-case basis.

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