Using a resolution function to regulate parameterizations of oceanic mesoscale eddy effects

Hallberg, Robert

doi:10.1016/j.ocemod.2013.08.007

Cited by 343 publications

(399 citation statements)

References 31 publications

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“…3) Eddy-rich ocean models: the majority of CMIP5 climate projections were undertaken using coarse (1° or coarser) ocean model components (typically with meridional refinement near the equator). At this grid spacing, the first baroclinic Rossby radius is resolved only near the equator (Hallberg 2013). Hewitt et al (2017) reviewed the improvements found in going toward eddy-poor/ eddy-rich regimes (1/4°-1/10°), with important consequences for large-scale biases (McClean et al 2011;Delworth et al 2012;Small et al 2014a;Hewitt et al 2016), heat uptake (e.g., Griffies et al 2015;Kuhlbrodt et al 2015), and ocean marine ecosystems (Saba et al 2016;McKiver et al 2015;Stock et al 2011).…”

Section: Future Prospects and Challengesmentioning

confidence: 99%

The Benefits of Global High Resolution for Climate Simulation: Process Understanding and the Enabling of Stakeholder Decisions at the Regional Scale

Roberts

Vidale

Senior

et al. 2018

Bulletin of the American Meteorological Society

117

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The time scales of the Paris Climate Agreement indicate urgent action is required on climate policies over the next few decades, in order to avoid the worst risks posed by climate change. On these relatively short time scales the combined effect of climate variability and change are both key drivers of extreme events, with decadal time scales also important for infrastructure planning. Hence, in order to assess climate risk on such time scales, we require climate models to be able to represent key aspects of both internally driven climate variability and the response to changing forcings. In this paper we argue that we now have the modeling capability to address these requirements—specifically with global models having horizontal resolutions considerably enhanced from those typically used in previous Intergovernmental Panel on Climate Change (IPCC) and Coupled Model Intercomparison Project (CMIP) exercises. The improved representation of weather and climate processes in such models underpins our enhanced confidence in predictions and projections, as well as providing improved forcing to regional models, which are better able to represent local-scale extremes (such as convective precipitation). We choose the global water cycle as an illustrative example because it is governed by a chain of processes for which there is growing evidence of the benefits of higher resolution. At the same time it comprises key processes involved in many of the expected future climate extremes (e.g., flooding, drought, tropical and midlatitude storms).

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Section: Future Prospects and Challengesmentioning

confidence: 99%

The Benefits of Global High Resolution for Climate Simulation: Process Understanding and the Enabling of Stakeholder Decisions at the Regional Scale

Roberts

Vidale

Senior

et al. 2018

Bulletin of the American Meteorological Society

117

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“…To properly resolve eddies, a ratio of two grid points per radius of defor-141 mation is needed (Hallberg, 2013 …”

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confidence: 99%

Dissolved iron transport pathways in the Ross Sea: Influence of tides and horizontal resolution in a regional ocean model

Mack

Dinniman

McGillicuddy

et al. 2017

Journal of Marine Systems

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Phytoplankton production in the Ross Sea is regulated by the availability of dissolved iron (dFe), a limiting micro-nutrient, whose sources include Circumpolar Deep Water, sea ice melt, glacial melt, and benthic sources (sediment efflux and remineralization). We employ a passive tracer dye to model the benthic dFe sources and track pathways from deep areas of the continental shelf to the surface mixed layer in simulations with and without tidal forcing, and at 5 and 1.5 km horizontal resolution. This, combined with dyes for each of the other dFe sources, provides an estimate of total dFe supply to surface waters. We find that tidal forcing increases the amount of benthic dye that covers the banks on the continental shelf. shelf, but spatial patterns differ between simulations, particularly along the ice shelf front. Benthic dFe supply in simulations shows an increase with tidal forcing and a decrease with higher resolution. The changes in benthic dFe supply control the difference in total supply between simulations. Overall, the total dFe supply from simulations varies from 5.60 to 7.95 µmol m −2 yr −1 , with benthic supply comprising 32-50%, comparing well with recent data and model synthesis. We suggest that including tides and using high horizontal resolution is important, especially when considering spatial variability of iron supply on the Ross Sea shelf.

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“…What constitutes adequate resolution then depends on the process in question. Hallberg (2013) suggest two grid cells per baroclinic Rossby radius gives a good representation of eddy fluxes, so we take e > 2 to be eddy resolving. If eddies have a characteristic size of ∼ 2 L 1 (i.e.…”

Section: Coastal Ocean Process Scales In a Global Contextmentioning

confidence: 99%

“…The simplest are just depth dependence (Wakelin et al, 2009) or based on horizontal shear (Smagorinsky, 1963). Combination of these with water column density structure (Hallberg, 2013) are likely to be most appropriate, but have not yet been tested in both the open and coastal ocean contexts.…”

Section: Vertical and Horizontal Mixing Parameterisationsmentioning

confidence: 99%

Prospects for improving the representation of coastal and shelf seas in global ocean models

et al. 2017

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Abstract. Accurately representing coastal and shelf seas in global ocean models represents one of the grand challenges of Earth system science. They are regions of immense societal importance through the goods and services they provide, hazards they pose and their role in global-scale processes and cycles, e.g. carbon fluxes and dense water formation. However, they are poorly represented in the current generation of global ocean models. In this contribution, we aim to briefly characterise the problem, and then to identify the important physical processes, and their scales, needed to address this issue in the context of the options available to resolve these scales globally and the evolving computational landscape.We find barotropic and topographic scales are well resolved by the current state-of-the-art model resolutions, e.g. nominal 1/12 • , and still reasonably well resolved at 1/4 • ; here, the focus is on process representation. We identify tides, vertical coordinates, river inflows and mixing schemes as four areas where modelling approaches can readily be transferred from regional to global modelling with substantial benefit. In terms of finer-scale processes, we find that a 1/12 • global model resolves the first baroclinic Rossby radius for only ∼ 8 % of regions < 500 m deep, but this increases to ∼ 70 % for a 1/72 • model, so resolving scales globally requires substantially finer resolution than the current state of the art.We quantify the benefit of improved resolution and process representation using 1/12 • global-and basin-scale northern North Atlantic nucleus for a European model of the ocean (NEMO) simulations; the latter includes tides and a k-ε vertical mixing scheme. These are compared with global stratification observations and 19 models from CMIP5. In terms of correlation and basin-wide rms error, the high-resolution models outperform all these CMIP5 models. The model with tides shows improved seasonal cycles compared to the highresolution model without tides. The benefits of resolution are particularly apparent in eastern boundary upwelling zones.To explore the balance between the size of a globally refined model and that of multiscale modelling options (e.g. finite element, finite volume or a two-way nesting approach), we consider a simple scale analysis and a conceptual grid refining approach. We put this analysis in the context of evolving computer systems, discussing model turnaround time, scalability and resource costs. Using a simple cost model compared to a reference configuration (taken to be a 1/4 • global model in 2011) and the increasing performance of the UK Research Councils' computer facility, we estimate an unstructured mesh multiscale approach, resolving process scales down to 1.5 km, would use a comparable share of the computer resource by 2021, the two-way nested multiscale approach by 2022, and a 1/72 • global model by 2026. However, we also note that a 1/12 • global model would not have a comparable computational cost to a 1 • global model in 2017 until 2027. Hence, we conc...

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Using a resolution function to regulate parameterizations of oceanic mesoscale eddy effects

Cited by 343 publications

References 31 publications

The Benefits of Global High Resolution for Climate Simulation: Process Understanding and the Enabling of Stakeholder Decisions at the Regional Scale

The Benefits of Global High Resolution for Climate Simulation: Process Understanding and the Enabling of Stakeholder Decisions at the Regional Scale

Dissolved iron transport pathways in the Ross Sea: Influence of tides and horizontal resolution in a regional ocean model

Prospects for improving the representation of coastal and shelf seas in global ocean models

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