Observational and numerical modeling methods for quantifying coastal ocean turbulence and mixing

Burchard, Hans; Craig, Peter D.; Gemmrich, Johannes; Haren, Hans van; Mathieu, Pierre-Philippe; Meier, H. E. Markus; Smith, W. A. M. Nimmo; Prandke, Hartmut; Rippeth, Tom P.; Skyllingstad, Eric D.; Smyth, William D.; Welsh, David J. S.; Wijesekera, H. W.

doi:10.1016/j.pocean.2007.09.005

Cited by 123 publications

(92 citation statements)

References 164 publications

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“…The representation of vertical mixing in ocean models remains an area that requires particular attention due to the different mixing schemes, related parameters and the often poorly quantified effects of numerical mixing (e.g. Buchard et al 2008). Regionally, the departures from the ensemble mean can exceed ±500 Cm, or 0.7 C in terms of the depth-averaged temperature (Fig.…”

Section: Time-mean and Amplitude Of The Seasonal Cyclementioning

confidence: 99%

Ocean heat content variability and change in an ensemble of ocean reanalyses

et al. 2015

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regions of the Pacific and Indian Oceans where the interannual variability of the ensemble mean exceeds ensemble spread, indicating that OHC variations are well-constrained by the available observations over the period [1993][1994][1995][1996][1997][1998][1999][2000][2001][2002][2003][2004][2005][2006][2007][2008][2009]. At deeper levels, the ORAs are less well-constrained by observations with the largest differences across the ensemble mostly associated with areas of high eddy kinetic energy, such as the Southern Ocean and boundary current regions. Spatial patterns of OHC change for the period 1997-2009 show good agreement in the upper 300 m and are characterized by a strong dipole pattern in the Pacific Ocean. There is less agreement in the patterns of change at deeper levels, potentially linked to differences in the representation of ocean dynamics, such as water mass formation processes. However, the Atlantic and Southern Oceans Abstract Accurate knowledge of the location and magnitude of ocean heat content (OHC) variability and change is essential for understanding the processes that govern decadal variations in surface temperature, quantifying changes in the planetary energy budget, and developing constraints on the transient climate response to external forcings. We present an overview of the temporal and spatial characteristics of OHC variability and change as represented by an ensemble of dynamical and statistical ocean reanalyses (ORAs). Spatial maps of the 0-300 m layer show large This paper is a contribution to the special issue on Ocean estimation from an ensemble of global ocean reanalyses, consisting of papers from the Ocean Reanalyses Intercomparsion Project (ORAIP), coordinated by CLIVAR-GSOP and GODAE OceanView. The special issue also contains specific studies using single reanalysis systems. The current work emphasizes the need to better observe the deep ocean, both for providing observational constraints for future ocean state estimation efforts and also to develop improved models and data assimilation methods.

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Section: Time-mean and Amplitude Of The Seasonal Cyclementioning

confidence: 99%

Ocean heat content variability and change in an ensemble of ocean reanalyses

et al. 2015

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“…These types of closure are respectively referred to as one-and twoequation models (Burchard et al, 2008). The turbulent model, most frequently used by the NEMO community and commonly called the TKE model, is a oneequation model suggested by Blanke and Delecluse (1993).…”

Section: The Mixing Lengthmentioning

confidence: 99%

Modelling turbulent vertical mixing sensitivity using a 1-D version of NEMO

2015

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Abstract. Through two numerical experiments, a 1-D vertical model called NEMO1D was used to investigate physical and numerical turbulent-mixing behaviour. The results show that all the turbulent closures tested (k + l from Blanke and Delecluse, 1993, and two equation models: generic length scale closures from Umlauf and Burchard, 2003) are able to correctly reproduce the classical test of Kato and Phillips (1969) under favourable numerical conditions while some solutions may diverge depending on the degradation of the spatial and time discretization. The performances of turbulence models were then compared with data measured over a 1-year period (mid-2010 to mid-2011) at the PAPA station, located in the North Pacific Ocean. The modelled temperature and salinity were in good agreement with the observations, with a maximum temperature error between −2 and 2 • C during the stratified period (June to October). However, the results also depend on the numerical conditions. The vertical RMSE varied, for different turbulent closures, from 0.1 to 0.3 • C during the stratified period and from 0.03 to 0.15 • C during the homogeneous period. This 1-D configuration at the PAPA station (called PAPA1D) is now available in NEMO as a reference configuration including the input files and atmospheric forcing set described in this paper. Thus, all the results described can be recovered by downloading and launching PAPA1D. The configuration is described on the NEMO site (http://www.nemo-ocean.eu/Using-NEMO/ Configurations/C1D_PAPA). This package is a good starting point for further investigation of vertical processes.

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“…through terrain following (s) or arbitrary Lagrangian-Eulerian (ALE) coordinates (Petersen et al., 2015). Also required are turbulence models suited for multiple boundary layers (Burchard et al, 2008) and a sophisticated representation of bottom friction. This can be achieved using a quadratic friction with a log-layer formulation (Blumberg and Mellor, 1987) and a semi-implicit bed stress implementation for numerical stability, given the large stresses and thin vertical layers.…”

Section: Tidesmentioning

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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Observational and numerical modeling methods for quantifying coastal ocean turbulence and mixing

Cited by 123 publications

References 164 publications

Ocean heat content variability and change in an ensemble of ocean reanalyses

Ocean heat content variability and change in an ensemble of ocean reanalyses

Modelling turbulent vertical mixing sensitivity using a 1-D version of NEMO

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

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