44 research outputs found
Approaches for the improvement of physical transport processes in numerical models of coastal oceans
In this thesis three approaches to improve the simulated transport processes in coastal ocean models are discussed. The first approach deals with the discretisation of the governing equations and provides a diagnostic tool to assess the accuracy of a numerical transport scheme. The second approach considers the validity of the governing equations itself and suggests an alternative inclusion of missing nonhydrostatic dynamics. The third approach presents the inclusion of unresolved wind wave effects into a coastal ocean model
Discrete variance decay analysis of spurious mixing
Expressions for local discrete variance decay (DVD) rates are directly
derived from discrete tracer equations without any assumptions on discrete
fluxes of the second moment. Spurious mixing (SM) associated with numerical
implementations of scalar advection and diffusion is thus estimated. The new
framework is shown to avoid the need for second-moment flux definition when
solved on finite-volume cell edges but still invoke certain second-moment
fluxes when the DVD rates are partitioned to participating cell nodes. These
implied discrete fluxes are shown to differ from those proposed in earlier
literature (but share the same dissipative part) and thus reveal the
non-uniqueness of their nature. They are shown to be ambiguous for high-order
advection schemes introducing uncertainty to the locality of any estimates
produced by a DVD approach. Additional damping of flux divergence through
temporal averaging or some coarse-graining is thus shown to be necessary.
Through the application of this technique, SM is found to be correlated with
the distribution of eddy kinetic energy. The contribution from vertical
advection to SM is found to be relatively small and correlated with the
distribution of buoyancy fluxes. The explored high-order schemes are found to
demonstrate levels of spurious mixing which may locally exceed background
physical mixing.Comment: Submitted to Ocean Modelling Manuscript number: OCEMOD-D-23-00145.
Name of funder: Deutsche Forschungsgemeinschaft. Grant agreement or award
number: 27476265
The large scale impact of offshore wind farm structures on pelagic primary productivity in the southern North Sea
The increasing demand for renewable energy is projected to result in a
40-fold increase in offshore wind electricity in the European Union by 2030.
Despite a great number of local impact studies for selected marine populations,
the regional ecosystem impacts of offshore wind farm structures are not yet
well assessed nor understood. Our study investigates whether the accumulation
of epifauna, dominated by the filter feeder Mytilus edulis (blue mussel), on
turbine structures affects pelagic primary productivity and ecosystem
functioning in the southern North Sea. We estimate the anthropogenically
increased potential distribution based on the current projections of turbine
locations and reported patterns of M. edulis settlement. This distribution is
integrated through the Modular Coupling System for Shelves and Coasts to
state-of-the-art hydrodynamic and ecosystem models. Our simulations reveal
non-negligible potential changes in regional annual primary productivity of up
to 8% within the offshore wind farm area, and induced maximal increases of the
same magnitude in daily productivity also far from the wind farms. Our setup
and modular coupling are effective tools for system scale studies of other
environmental changes arising from large-scale offshore wind-farming such as
ocean physics and distributions of pelagic top predators.Comment: 17 pages, 6 figures, re-revised manuscript submitted to Hydrobiologi
Split-explicit external mode solver in finite volume sea ice ocean model FESOM2
A novel split-explicit (SE) external mode solver for the Finite volumE Sea
ice-Ocean Model (FESOM2) is presented. It is compared with the semi-implicit
(SI) solver currently used in FESOM2. The SE solver utilises a dissipative
asynchronous (forward-backward) time-stepping scheme. Its implementation with
Arbitrary Lagrangian-Eulerian (ALE) vertical coordinates like Z-star and
Z-tilde is explored. The comparisons are performed through multiple test cases
involving idealised and realistic global simulations. The SE solver
demonstrates lower phase errors and dissipation, but maintain a simulated mean
ocean state very similar to the SI solver. The SE solver is also shown to
possess better run-time performance and parallel scalability across all tested
workloads.Comment: Submitted to Geoscientific Model Development number: GMD-2023-208.
Development code for FESOM2.5 with explicit subcycling available at:
https://zenodo.org/doi/10.5281/zenodo.10040943. Name of funder: Deutsche
Forschungsgemeinschaft. Grant agreement or award number: 27476265
Modular System for Shelves and Coasts (MOSSCO v1.0) - a flexible and multi-component framework for coupled coastal ocean ecosystem modelling
Shelf and coastal sea processes extend from the atmosphere through the water
column and into the sea bed. These processes are driven by physical, chemical,
and biological interactions at local scales, and they are influenced by
transport and cross strong spatial gradients. The linkages between domains and
many different processes are not adequately described in current model systems.
Their limited integration level in part reflects lacking modularity and
flexibility; this shortcoming hinders the exchange of data and model components
and has historically imposed supremacy of specific physical driver models. We
here present the Modular System for Shelves and Coasts (MOSSCO,
http://www.mossco.de), a novel domain and process coupling system
tailored---but not limited--- to the coupling challenges of and applications in
the coastal ocean. MOSSCO builds on the existing coupling technology Earth
System Modeling Framework and on the Framework for Aquatic Biogeochemical
Models, thereby creating a unique level of modularity in both domain and
process coupling; the new framework adds rich metadata, flexible scheduling,
configurations that allow several tens of models to be coupled, and tested
setups for coastal coupled applications. That way, MOSSCO addresses the
technology needs of a growing marine coastal Earth System community that
encompasses very different disciplines, numerical tools, and research
questions.Comment: 30 pages, 6 figures, submitted to Geoscientific Model Development
Discussion
The impact of advection schemes on restratifiction due to lateral shear and baroclinic instabilities
This paper quantifies spurious dissipation and mixing of various advection schemes in idealised experiments of lateral shear and baroclinic instabilities in numerical simulations of a re-entrant Eady channel for configurations with large and small Rossby numbers. In addition, a two-dimensional barotropic shear instability test case is used to examine numerical dissipation of momentum advection in isolation, without any baroclinic effects. Effects of advection schemes on the evolution of background potential energy and the dynamics of the restratification process are analysed. The advection schemes for momentum and tracers are considered using several different methods including a recently developed local dissipation analysis. As highly accurate but computationally demanding schemes we apply WENO and MP5, and as more efficient lower-order total variation diminishing (TVD) schemes we use among others the SPL-max-View the MathML source13 and a third-order-upwind scheme. The analysis shows that the MP5 and SPL-max-View the MathML source13 schemes provide the most accurate results. Following our comprehensive analysis of computational costs, the MP5 scheme is approximately 2.3 times more expensive in our implementation. In contrast to the configuration with a small Rossby number, in which significant differences between schemes are apparent, the different advection schemes behave similarly for a larger Rossby number. Regions of high numerical dissipation are shown to be associated with low grid Reynolds numbers. The major outcome of the present study is that generally positive global numerical dissipation and positive background potential energy evolution delay the restratification process
Challenges and prospects for dynamical cores of oceanic models across all scales
International audienceThis poster outlines an initiative to bring together the world-wide leading researchers actively contributing to the development of oceanic model dynamical cores irrespective of target applications (regional, coastal, or global). The first community for the numerical modeling ofthe global, regional and coastal ocean (COMMODORE) workshop (https://commodore2018.sciencesconf.org/) has been organized in Paris in September 2018 [1]. In total, the participants represented 15 oceanic dynamical cores among the most widely used by the research and operational community. The present poster summarizes the challenges and prospects for oceanic numerical cores across all scales discussed during the workshop. In particular, identified challenges to be addressed include strategies for multi-resolution, energy consistency and resolved/unresolved scales coupling, the design of vertical coordinates and their link with spurious numerical mixing, the inclusion of non-hydrostatic pressure contribution within existing primitive equations models, and the proper treatment of wetting and drying
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A direct comparison of a depth-dependent Radiation stress formulation and a Vortex force formulation within a three-dimensional coastal ocean model
In this study a model system consisting of the three-dimensional General Estuarine Transport Model (GETM) and the third generation wind wave model SWAN was developed. Both models were coupled in two-way mode. The effects of waves were included into the ocean model by implementing the depth-dependent Radiation stress formulation (RS) of Mellor (2011a) and the Vortex force formulation (VF) presented by Bennis et al. (2011). Thus, the developed model system offers a direct comparison of these two formulations. The enhancement of the vertical eddy viscosity due to the energy transfer by white capping and breaking waves was taken into account by means of injecting turbulent kinetic energy at the surface. Wave-current interaction inside the bottom boundary layer was considered as well.
The implementation of both wave-averaged formulations was validated against three flume experiments. One of these experiments with long period surface waves (swell), had not been evaluated before. The validation showed the capability of the model system to reproduce the three-dimensional interaction of waves and currents. For the flume test cases the wave-induced water level changes (wave set-up and set-down) and the corresponding depth-integrated wave-averaged velocities were similar for RS and VF. Both formulations produced comparable velocity profiles for short period waves. However, for large period waves, VF overestimated the wave set-down near the main breaking points and RS showed artificial offshore-directed transport at the surface where wave shoaling was taking place. Finally the validated model system was applied to a realistic barred beach scenario. For RS and VF the resulting velocity profiles were similar after being significantly improved by a roller evolution method.
Both wave-averaged formulations generally provided similar results, but some shortcomings were revealed. Although VF partly showed significant deviations from the measurements, its results were still physically reasonable. In contrast, RS showed unrealistic offshore-directed transport in the wave-shoaling regions and close to steep bathymetry.This is an author's peer-reviewed manuscript, as accepted by the publisher. The published article is copyrighted by Elsevier and can be found at: http://www.journals.elsevier.com/ocean-modelling/.Keywords: GETM, Near-shore hydrodynamics, Radiation stress, Vortex force, Wave mixing effects, Wave-current interaction, SWANKeywords: GETM, Near-shore hydrodynamics, Radiation stress, Vortex force, Wave mixing effects, Wave-current interaction, SWA