Scottish Marine and Freshwater Science Volume 5 Number 3: The Science of Deepwater Oil Spills - Results from the 2013 Marine Scotland Science Workshop

Theme 2 - Circulation modelling

State Of The Art

Presentations:

1. Operational modelling (John Siddorn, UK Met Office).
2. Model development (Sarah Wakelin, NOC-L).
3. Small scale processes (Vasyl Vlasenko, Plymouth University).
4. International perspective (Lars R. Hole, Met No)

Presentations were made by representatives from the UK Met Office, the UK National Oceanographic Centre - Liverpool, Plymouth University and the Norwegian Meteorological Institute. A brief review of the state-of-the-art of hydrodynamic regional models for the UK continental shelf was presented. A validation of the FOAM AMM7 modelled currents in the FSC was presented. Validation of other regional scale models were also presented, including currents, CTD, tracer tracks, drifters, and sub-surface fluxes. A comparison with a real oil spill was also shown. Some attention was also paid to small scale processes that require high resolution modelling, such as internal waves and some wind driven currents.

Specific items identified by the workshop participants in the discussions to characterise the state of the art were:

• Oceanographic Fronts: Oceanographic fronts are often areas of enhanced convergence and vertical velocities (sinking). Such fronts are known to exist in the FSC, and require consideration. Are such features captured by the current models?
• Data Assimilation: This was again identified as a priority to enhance present modelling in the FSC.
• Temperature/Salinity Structure: The vertical distribution of temperate and salinity in the FSC is well described by the repeat monitoring that is undertaken there. Temperature/salinity profiles should be used more to test the skill of circulation models. The vertical density structure is a key factor when considering the initial dynamics of a released oil plume.
• Model Validation: In the presentations of models of the FSC, few talks mentioned model validation using observations. More information on model validation, especially sub-surface currents and processes is needed.
• Explaining the Models: If models are to become the basis of most of the dispersion planning and prediction in the FSC, then we need better simple descriptions of ocean models in order to explain what is being done.
• Expert Interpretations: Expert interpretation is needed to aid end-users' understanding and use of circulation models and their outputs.
• Stokes Drift: It was questioned to what extent this dispersion process (resulting from the interaction of waves and currents) is incorporated into current dispersion models in the FSC, and if observations were available to show the magnitude of this dispersion mechanism under the extreme conditions found in the FSC?
• Waves in UK Models: The workshop questioned to what extent surface waves and their interactions were incorporated in the current generation of circulation models, particularly those used by UK institutes.
• Regional Model Suitability: It was suggested that different models may work best in different regions (e.g. the FSC, the Norwegian Sea, the Iceland Basin, the UK Continental shelf). The question was put, which models work best in which region?
• Model Applications: It was felt that there had been a focus on the operational use of models in the FSC, and less on the use of models to hind cast events or as planning tools. These different uses support spill response vs environmental assessment.
• Bathymetry: It was noted that there are many bathymetric effects on circulation and mixing in the FSC. It was questioned how well bathymetric effects are included in the current generation of models, and if accurate bathymetries are available for the region.

• Meteorological Models: It was recognised that most meteorological forcing data fields come from models, and hence a review is needed of the available meteorological forcing models, their strengths and their weaknesses.
• Circulation Models: Similarly a review of all available ocean circulation models could be useful in order to identify input for spill models.
• Model Skill: One validation method might be to test model skills in terms of predicted trajectories, including above deep water, the shelf edge and in coastal waters. Here drifters would provide useful in situ validation data.
• Parameterised Processes: Most models parameterise sub-grid scale processes and do this in differing ways. A discussion is needed of the sub-scale physics included in each model.
• Probabilistic Ensemble vs Deterministic: There is a distinction between probabilistic ensemble vs deterministic model runs. However, the workshop asked what is more valuable for the end-user?
• Driving Factors Behind Model Choice?: What is the driving factor behind the choice an offshore operator/regulator/monitoring agency/environmental consultancy makes as to which model to purchase and use? In reality it was thought that it may be the cost and availability of a model rather than its applicability or accuracy. Additionally, circulation models may be being selected simply as they meet the input requirements of spill models (e.g. format/scale) rather than being the most skilful models.
• IT Considerations: There are also issues concerning the hardware (e.g. data storage, processing power, etc.) that may influence model selection, mode resolution and model use.
• Understanding by the Regulator: The workshop discussed if there was a lack of critical understanding by the regulator of the complexity of the field of hydrodynamic modelling and oil spill modelling. This might be a barrier to the correct selection and application of models in the FSC.

Knowledge Gaps

• A Holistic Modelling System: Currently there are many models that include the FSC region, each including different processes and at different geographical scales. There should be an effort to bring these different models together in order to create an holistic modelling system of the region. No single circulation model seems to be able to capture all relevant processes at the moment.
• Lack of Measurements: There is still a need to provide in situ measurements in order to support high resolution modelling. Modelling and observation must be performed at similar time and space scales.
• Lack of Validation: There are still very few comparisons between measurements and models in the FSC.
• Minimum Standards: We need a definition of what is the minimum requirement for an underlying hydrodynamic model used to support oil spill prediction in the FSC.
• Comparison Exercise: We need a systematic comparison exercise between models, and between models and observations in the FSC area.
• Model Ensembles: The use of model ensembles (different models using the same parameters and forcing datasets) and ensemble runs (individual models run with parameter perturbations and/or different forcing datasets to account for uncertainties in those) should be explored and compared to single model runs in order to include and quantify potential variability.
• Standard Outputs: We need standard (in terms of temporal and spatial resolution, region and format) FSC model outputs so that users could run their own comparisons between models and their various outputs. If this is unrealistic, an open library of post-processing scripts for model output re-formatting into common standards could achieve the same objective.
• Research Dissemination: There exists an end-user knowledge gap concerning what is available from the academic research community. More focus is needed on user-friendly dissemination to the end user, not just peer reviewed publications.
• Different Model Uses: We must acknowledge the different needs of planning scenarios vs emergency response, and create a system to support these different needs.

Future Directions

• Benchmark Datasets: It was suggested that "benchmark" datasets of driving forces should be established (e.g. wind fields/boundary conditions) in order to facilitate inter-model comparisons.
• Flexible Data Assimilation: Models with flexible data assimilation schemes should be developed. These could target where an incident occurs and improve models locally where needed.
• Remote Sensing: Remote sensing to provide real-time data for assimilation into models should be considered (e.g. HF Radar for surface currents and waves data).
• Industry Data: Industry (e.g. ADCP) data should be used more, and made more available to the research and modelling communities.
• Community Disconnect?: Workshop participants thought there was a disconnect between end-users, modellers and experts, and that a mechanism was needed in order to close this gap. This should include regional partners as well as national ones, for example through the EU and including Norway. Likewise, better connection between government, academia and industry is needed, possibly through the industry bodies (e.g. Oil & Gas UK) and regulators (e.g. DECC etc, MS, MMO).
• Real-time Data: For operational modelling, and data assimilation into operational models, real-time ocean data needs to be transmitted to modellers. The systems needed to do this (e.g. the Global Telecommunications System, GTS) should be investigated.
• Funding of Model Development: Industry should be encouraged to the development of regional circulation models, in collaboration with Government and funding councils.
• Standard Model Outputs: Standard model outputs for different regions in standard formats, freely available for easy comparison, including the forcing datasets.
• Model Challenges: There should be organised model comparisons, both between different models, and between models and observations in order to test their validity, consistency, strengths and weaknesses.
• Model Resolution Limit: As we go to higher spatial and temporal resolution, will there be a limit to the cost-benefit?
• Oil Spill Modelling Priorities: There should be an exercise to prioritise what is important for oil spill modelling, and then these priorities should be translated back to priority setting for hydrodynamic modelling.