Simulating the Agulhas system in global ocean models – nesting vs. multi-resolution unstructured meshes

Biastoch, Arne; Sein, Dmitry V.; Durgadoo, Jonathan V.; Wang, Qiang; Danilov, Sergey

doi:10.1016/j.ocemod.2017.12.002

Cited by 26 publications

(30 citation statements)

References 79 publications

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“…Features such as ocean mesoscale eddies are now increasingly present in ocean and ocean‐atmosphere simulations. In some instances increased resolution results in better representation of boundary currents such as the Gulf Stream, the Agulhas‐, Brazil‐, and Malvinas currents (e.g., Biastoch et al, ; Griffies et al, ; Hewitt et al, ; Murakami et al, ; Sein et al, ; Small et al, ). Similarly, fronts, and the associated gradients of temperature and salinity, are more sharply defined.…”

Section: Introductionmentioning

confidence: 99%

The Atlantic Meridional Overturning Circulation in High‐Resolution Models

et al. 2020

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The Atlantic meridional overturning circulation (AMOC) represents the zonally integrated stream function of meridional volume transport in the Atlantic Basin. The AMOC plays an important role in transporting heat meridionally in the climate system. Observations suggest a heat transport by the AMOC of 1.3 PW at 26°N-a latitude which is close to where the Atlantic northward heat transport is thought to reach its maximum. This shapes the climate of the North Atlantic region as we know it today. In recent years there has been significant progress both in our ability to observe the AMOC in nature and to simulate it in numerical models. Most previous modeling investigations of the AMOC and its impact on climate have relied on models with horizontal resolution that does not resolve ocean mesoscale eddies and the dynamics of the Gulf Stream/North Atlantic Current system. As a result of recent increases in computing power, models are now being run that are able to represent mesoscale ocean dynamics and the circulation features that rely on them. The aim of this review is to describe new insights into the AMOC provided by high-resolution models. Furthermore, we will describe how high-resolution model simulations can help resolve outstanding challenges in our understanding of the AMOC. Key Points:• Observations and high-resolution models have changed view on the AMOC pathways • High-resolution models suggest the presence of previously unknown high-frequency AMOC variability • High-resolution models allow to estimate the intrinsic/chaotic component of the AMOCCorrespondence to:

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Section: Introductionmentioning

confidence: 99%

The Atlantic Meridional Overturning Circulation in High‐Resolution Models

et al. 2020

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“…With both the cold and the warm water routes of the upper MOC branches and a portion of the lower MOC branch passing through the Cape Basin, it is evident that this is a critical region for observing MOC‐related flows. Recognition of the key roles that ocean dynamics in the Cape Basin play in the MOC is not new—Numerous previous experiments have studied aspects of the flows in the region using ship sections (e.g., Arhan et al, ; Duncombe Rae, ; Ganachaud, ; Gladyshev et al, ; Whittle et al, ), deep profiling floats (Lutjeharms et al, ; Richardson et al, ; van Aken et al, ), Argo float‐altimetry syntheses (Majumder & Schmid, ; Rusciano et al, ; Schmid, ), and numerical models (e.g., Biastoch et al, , , ; Rimaud et al, ; Weijer & van Sebille, ). Historical in situ measurements using moored instruments in the region have been focused in the Agulhas Current and Agulhas Retroflection region farther east (Baker‐Yeboah et al, , ; Beal, ; Beal et al, ; Bryden et al, ) and in the greater Agulhas Current system farther south or north (Duncombe Rae et al, ; Garzoli & Gordon, ; Goni et al, ).…”

Section: Introductionmentioning

confidence: 99%

Shallow and Deep Eastern Boundary Currents in the South Atlantic at 34.5°S: Mean Structure and Variability

et al. 2019

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The first in situ continuous full‐water‐column observations of the eastern boundary currents (EBCs) at 34.5°S in the South Atlantic are obtained using 23 months of data from a line of Current and Pressure recording Inverted Echo Sounders (CPIES) spanning the Cape Basin. The CPIES are used to evaluate the mean structure of the EBC, the associated water masses, and the volume transport variability. The estimated northward time‐mean Benguela Current absolute geostrophic transport is 24 Sv, with a temporal standard deviation of 17 Sv. Beneath this current the time‐mean transport is southward, indicating the presence of a deep‐EBC (DEBC), with a time‐mean transport of 12 Sv, and a standard deviation of 17 Sv. Offshore of these currents, the shallow and deep flows are more variable with weak time means, likely influenced by Agulhas Rings transiting through the region. Hydrographic data collected along the CPIES line demonstrate that the DEBC is carrying recently ventilated North Atlantic Deep Water, as it flows along the continental slope. This is consistent with a previously hypothesized interior pathway bringing recently ventilated North Atlantic Deep Water from the Deep Western Boundary Current across the Atlantic to the Cape Basin. The observations further indicate that much of the DEBC must recirculate within the basin. Spectral analyses of the shallow and deep EBC transport time series demonstrate that the strongest variability occurs on timescales ranging from 30 to 90 days, associated with the propagation of Agulhas Rings.

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“…Local mesh refinement can be realized easily, even in many different regions simultaneously, and the required work is mainly to design meshes with refinement in physically meaningful regions. For example, we can use high resolution in a chosen ocean basin in an otherwise coarse global ocean (Q. Wang et al, ; Wekerle, Wang, Danilov, et al, ; Wekerle, Wang, von Appen, et al, ) or vary the resolution continuously in a global model according to the strength of local eddy variability (Biastoch et al, ; Sein et al, ) or local Rossby radius (Sein et al, ).…”

Section: Introductionmentioning

confidence: 99%

Improving the Upper‐Ocean Temperature in an Ocean Climate Model (FESOM 1.4): Shortwave Penetration Versus Mixing Induced by Nonbreaking Surface Waves

Wang

Shu

et al. 2019

J Adv Model Earth Syst

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As the first mature global ocean general circulation model based on unstructured-mesh methods, the multiresolution Finite Element Sea ice-Ocean Model (FESOM) has shown great capability in reconstructing the ocean and sea ice in both standalone and coupled simulations at a relatively low computational cost. Parameterizations of some important processes, including the vertical mixing induced by surface waves, however, are still missing, contributing to temperature biases in the upper ocean. In this work we incorporate the vertical mixing induced by nonbreaking surface waves derived from a wave model into FESOM and compare its effect with that of shortwave penetration, another key process to vertically redistribute the heat in the upper ocean. Numerical experiments with and without the shortwave penetration scheme and the nonbreaking surface wave mixing reveal that both processes ameliorate the simulation of upper-ocean temperature in middle and low latitudes mainly on the summer hemisphere. The role of nonbreaking surface waves is more pronounced in decreasing the mean cold biases at 50 m (by 1.0°C, in comparison to 0.5°C achieved by applying shortwave penetration). We conclude that the incorporation of mixing induced by nonbreaking surface waves into FESOM is practically very helpful and suggest that it needs to be considered in other ocean climate models as well.Plain Language Summary Nowadays, numerical ocean, weather, and climate forecasts play an important role in the daily life of human beings. An accurate prediction could help us prepare day-to-day activities orderly. However, the prediction ability has been much lower than expected. As an example, ocean models often simulate a warmer sea surface temperature and cooler subsurface (30-100 m deep) temperature in subtropical oceans, especially in summer, which can lead to big errors in the weather and climate forecasting. This situation was partly alleviated by distributing solar radiation in the upper ocean rather than only heating up the ocean surface. Although shortwave penetration makes some improvement on ocean model performance, it is still far from solving the common simulated temperature bias in the upper ocean. The simulated temperature is considerably improved by incorporating the mixing induced by nonbreaking surface waves into the new generation ocean model FESOM. It turns out that the nonbreaking wave is more capable in ameliorating the simulated upper-ocean temperature than the shortwave penetration.

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Simulating the Agulhas system in global ocean models – nesting vs. multi-resolution unstructured meshes

Cited by 26 publications

References 79 publications

The Atlantic Meridional Overturning Circulation in High‐Resolution Models

The Atlantic Meridional Overturning Circulation in High‐Resolution Models

Shallow and Deep Eastern Boundary Currents in the South Atlantic at 34.5°S: Mean Structure and Variability

Improving the Upper‐Ocean Temperature in an Ocean Climate Model (FESOM 1.4): Shortwave Penetration Versus Mixing Induced by Nonbreaking Surface Waves

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