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  • 1
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    Simulations for CMIP6 With the AWI Climate Model AWI‐CM‐1‐1 (2020)
    AMER GEOPHYSICAL UNION
    In:  EPIC3Journal of Advances in Modeling Earth Systems, AMER GEOPHYSICAL UNION, 12(9), ISSN: 1942-2466
    Details
    Publication Date: 2020-10-05
    Description: The Alfred Wegener Institute Climate Model (AWI‐CM) participates for the first time in the Coupled Model Intercomparison Project (CMIP), CMIP6. The sea ice‐ocean component, FESOM, runs on an unstructured mesh with horizontal resolutions ranging from 8 to 80 km. FESOM is coupled to the Max Planck Institute atmospheric model ECHAM 6.3 at a horizontal resolution of about 100 km. Using objective performance indices, it is shown that AWI‐CM performs better than the average of CMIP5 models. AWI‐CM shows an equilibrium climate sensitivity of 3.2°C, which is similar to the CMIP5 average, and a transient climate response of 2.1°C which is slightly higher than the CMIP5 average. The negative trend of Arctic sea‐ice extent in September over the past 30 years is 20–30% weaker in our simulations compared to observations. With the strongest emission scenario, the AMOC decreases by 25% until the end of the century which is less than the CMIP5 average of 40%. Patterns and even magnitude of simulated temperature and precipitation changes at the end of this century compared to present‐day climate under the strong emission scenario SSP585 are similar to the multi‐model CMIP5 mean. The simulations show a 11°C warming north of the Barents Sea and around 2°C to 3°C over most parts of the ocean as well as a wetting of the Arctic, subpolar, tropical, and Southern Ocean. Furthermore, in the northern middle latitudes in boreal summer and autumn as well as in the southern middle latitudes, a more zonal atmospheric flow is projected throughout the year.
    Repository Name: EPIC Alfred Wegener Institut
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  • 2
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    Influence of mixing parametrization scheme on properties of Atlantic Water in the Arctic Ocean (2017)
    EGU
    In:  EPIC3European Geosciences Union General Assembly 2017, 2017-04-23-2017-04-28EGU
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    Publication Date: 2017-11-13
    Repository Name: EPIC Alfred Wegener Institut
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  • 3
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    Simulating the Agulhas system in global ocean models – nesting vs. multi-resolution unstructured meshes (2018)
    ELSEVIER SCI LTD
    In:  EPIC3Ocean Modelling, ELSEVIER SCI LTD, 121, pp. 117-131, ISSN: 1463-5003
    Details
    Publication Date: 2018-02-28
    Description: Many questions in ocean and climate modelling require the combined use of high resolution, global coverage and multi-decadal integration length. For this combination, even modern resources limit the use of traditional structured-mesh grids. Here we compare two approaches: A high-resolution grid nested into a global model at coarser resolution (NEMO with AGRIF) and an unstructured-mesh grid (FESOM) which allows to variably enhance resolution where desired. The Agulhas system around South Africa is used as a testcase, providing an energetic interplay of a strong western boundary current and mesoscale dynamics. Its open setting into the horizontal and global overturning circulations also requires global coverage. Both model configurations simulate a reasonable large-scale circulation. Distribution and temporal variability of the wind-driven circulation are quite comparable due to the same atmospheric forcing. However, the overturning circulation differs, owing each model’s ability to represent formation and spreading of deep water masses. In terms of regional, high-resolution dynamics, all elements of the Agulhas system are well represented. Owing to the strong nonlinearity in the system, Agulhas Current transports of both configurations and in comparison with observations differ in strength and temporal variability. Similar decadal trends in Agulhas Current transport and Agulhas leakage are linked to the trends in wind forcing. Although the number of 3D wet grid points used in FESOM is similar to that in the nested NEMO, FESOM uses about two times the number of CPUs to obtain the same model throughput (in terms of simulated model years per day). This is feasible due to the high scalability of the FESOM code.
    Repository Name: EPIC Alfred Wegener Institut
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  • 4
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    Finite-Element Sea Ice Model (FESIM), version 2 (2015)
    EGU
    In:  EPIC3Geosci. Model Dev., EGU, 8, pp. 1747-1761
    Details
    Publication Date: 2016-11-29
    Description: Abstract. The Finite-Element Sea Ice Model (FESIM), used as a component of the Finite-Element Sea ice Ocean Model, is presented. Version 2 includes the elastic-viscous-plastic (EVP) and viscous-plastic (VP) solvers and employs a flux corrected transport algorithm to advect the ice and snow mean thicknesses and concentration. The EVP part also includes a modified approach proposed recently by Bouillon et al. (2013), which is characterized by an improved stability compared to the standard EVP approach. The model is formulated on unstructured triangular meshes. It assumes a collocated placement of ice velocities, mean thicknesses and concentration at mesh vertices, and relies on piecewise-linear (P1) continuous elements. Simple tests for the modified EVP and VP solvers are presented to show that they may produce very close results provided the number of iterations is sufficiently high.
    Repository Name: EPIC Alfred Wegener Institut
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  • 5
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    Ocean modeling on unstructured meshes (2013)
    ELSEVIER SCI LTD
    In:  EPIC3Ocean Modelling, ELSEVIER SCI LTD, 69, pp. 195-210, ISSN: 1463-5003
    Details
    Publication Date: 2019-07-17
    Description: Unstructured meshes are common in coastal modeling, but still rarely used for modeling the large-scale ocean circulation. Existing and new projects aim at changing this situation by proposing models enabling a regional focus (multiresolution) in global setups, without nesting and open boundaries. Among them, finite-volume models using the C-grid discretization on Voronoi-centroidal meshes or cell-vertex quasi-B-grid discretization on triangular meshes work well and offer the multiresolution functionality at a price of being 2 to 4 times slower per degree of freedom than structured-mesh models. This is already sufficient for many practical tasks and will be further improved as the number of vertical layers is increased. Approaches based on the finite-element method, both used or proposed, are as a rule slower at present. Most of staggered discretizations on triangular or Voronoi meshes allow spurious modes which are difficult to filter on unstructured meshes. The ongoing research seeks how to handle them and explores new approaches where such modes are absent. Issues of numerical efficiency and accurate transport schemes are still important, and the question on parameterizations for multiresolution meshes is hardly explored at all. The review summarizes recent developments the main practical result of which is the emergence of multiresolution models for simulating large-scale ocean circulation.
    Repository Name: EPIC Alfred Wegener Institut
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  • 6
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    A comparison of viscous-plastic sea ice solvers with and without replacement pressure (2017)
    ELSEVIER SCI LTD
    In:  EPIC3Ocean Modelling, ELSEVIER SCI LTD, 115, pp. 59-69, ISSN: 1463-5003
    Details
    Publication Date: 2017-07-27
    Repository Name: EPIC Alfred Wegener Institut
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  • 7
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    Variability of the oceanic bottom pressure from sensor observations and ocean models (2017)
    EGU
    In:  EPIC3European Geosciences Union General Assembly Vienna | Austria | 23–28 April 2017, 2017-04-23Vienna, EGU
    Details
    Publication Date: 2017-07-10
    Description: We discuss time series of ocean bottom pressure (OBP) computed by the Finite Element Sea Ice-Ocean Model (FESOM) driven by realistic forcing. The influence of atmospheric pressure and mesoscale eddies on the OBP and surface height anomalies on time scales up to years was investigated. Also, we estimated space and time scales of mass variability simulated by both climate-type (resolution about 1 degree) and eddy resolving (down to about 10km) versions of the model. We analyze the African sector of the Southern Ocean. A part of the OBP variance there is associated with eddy activity (especially in the Agulhas region) and explore its respective contribution. Assessment of averaging interval of simulated data for the purpose of minimizing aliasing in variability of OBP is additionally carried out. An important aspect of this study is the comparison of modeled and in situ OBP records. High frequency measurements of OBP with sub-daily resolution available from Pressure Inverted Echo Sounders (PIES) used to infer temporal co-spectra of OBP variability. The PIES are placed along the prime meridian south of Africa can be used to evaluate variations of both barotropic and baroclinic geostrophic transport fluctuations of the Antarctic Circumpolar Current and verify corresponding GRACE estimates. The distance between PIES stations is chosen to resolve the major oceanic fronts for this region, which allows us to compare co-spectra of observed and simulated OBP variability. A contribution of DFG SPP 1788 and 1257
    Repository Name: EPIC Alfred Wegener Institut
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  • 8
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    The adaptive EVP method for solving the sea ice momentum equation (2016)
    ELSEVIER SCI LTD
    In:  EPIC3Ocean Modelling, ELSEVIER SCI LTD, ISSN: 1463-5003
    Details
    Publication Date: 2016-04-06
    Description: Stability and convergence of the modified EVP implementation of the visco-plastic sea ice rheology by Bouillon et al., Ocean Modell., 2013, is analyzed on B- and C-grids. It is shown that the implementation on a B-grid is less restrictive with respect to stability requirements than on a C-grid. On C-grids convergence is sensitive to the discretization of the viscosities. We suggest to adaptively vary the parameters of pseudotime subcycling of the modified EVP scheme in time and space to satisfy local stability constraints. This new approach generally improves the convergence of the modified EVP scheme and hence its numerical efficiency. The performance of the new “adaptive EVP” approach is illustrated in a series of experiments with the sea ice component of the MIT general circulation model (MITgcm) that is formulated on a C-grid
    Repository Name: EPIC Alfred Wegener Institut
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  • 9
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    Impact of atmospheric forcing data on simulations of the Laptev Sea polynya dynamics using the sea-ice ocean model FESOM (2011)
    AMER GEOPHYSICAL UNION
    In:  EPIC3Journal of Geophysical Research-Oceans, AMER GEOPHYSICAL UNION, 116(C12038), pp. 1-18, ISSN: 0148-0227
    Details
    Publication Date: 2019-07-17
    Description: The polynyas of the Laptev Sea are regions of particular interest due to the strong formation of Arctic sea-ice. In order to simulate the polynya dynamics and to quantify ice production, we apply the Finite Element Sea-Ice Ocean Model FESOM. In previous simulations FESOM has been forced with daily atmospheric NCEP (National Centers for Environmental Prediction) 1. For the periods 1 April to 9 May 2008 and 1 January to 8 February 2009 we examine the impact of different forcing data: daily and 6-hourly NCEP reanalyses 1 (1.875° × 1.875°), 6-hourly NCEP reanalyses 2 (1.875° × 1.875°), 6-hourly analyses from the GME (Global Model of the German Weather Service) (0.5° × 0.5°) and high-resolution hourly COSMO (Consortium for Small-Scale Modeling) data (5 km × 5 km). In all FESOM simulations, except for those with 6-hourly and daily NCEP 1 data, the openings and closings of polynyas are simulated in principle agreement with satellite products. Over the fast-ice area the wind fields of all atmospheric data are similar and close to in situ measurements. Over the polynya areas, however, there are strong differences between the forcing data with respect to air temperature and turbulent heat flux. These differences have a strong impact on sea-ice production rates. Depending on the forcing fields polynya ice production ranges from 1.4 km3 to 7.8 km3 during 1 April to 9 May 2011 and from 25.7 km3 to 66.2 km3 during 1 January to 8 February 2009. Therefore, atmospheric forcing data with high spatial and temporal resolution which account for the presence of the polynyas are needed to reduce the uncertainty in quantifying ice production in polynyas.
    Repository Name: EPIC Alfred Wegener Institut
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  • 10
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    Two finite-volume unstructured mesh models for large-scale ocean modeling (2012)
    ELSEVIER SCI LTD
    In:  EPIC3Ocean Modelling, ELSEVIER SCI LTD, 47, pp. 14-25, ISSN: 1463-5003
    Details
    Publication Date: 2019-07-17
    Description: Two approaches pertaining to modeling large-scale ocean circulation on unstructured meshes are described. Both use the finite-volume ideology, unstructured surface triangular mesh and geopotential vertical coordinate, and promise better numerical efficiency than P1–P1 finite element models. The first one is formulated on median-dual control volumes for all variables and presents a finite-volume implementation of P1–P1 finite-element discretization (A-grid). The second one differs by the cell-centered placement of horizontal velocities (quasi-B-grid). Two practical tasks have to be solved to ensure their stable performance in long-term simulations. For triangular A-grids, it is the stabilization against pressure modes triggered by the stepwise bottom topography. The proposed solution preserves volume and tracers by introducing a composite representation for the horizontal velocity (with an elementwise- constant velocity correction). The quasi-B-grid setup is free of pressure modes but requires efficient filtering and dissipation in the momentum equation because of its too large velocity space. Implementations of momentum advection and viscosity that serve this goal are proposed. Both setups show stable performance and similar numerical efficiency, as exemplified by simulations of a baroclinic channel flow and circulation in the North Atlantic.
    Repository Name: EPIC Alfred Wegener Institut
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