Larsen J, Maar M, Brüning T, She J, Mohn C. 2017. Flexsem: A new method for offline ocean modelling. Aarhus University, DCE – Danish Centre for Environment and Energy, 28 pp. Technical Report from DCE – Danish Centre for Environment and Energy No. 105.
TR105.pdfAssessment of complex marine ecosystems requires a detailed understanding of processes, drivers and their interactions across multiple scales. This information is exceedingly provided by complex three-dimensional (3D), often simultaneously online coupled physical and ecosystem models, setting great demands on computing and operating resources and skills. The present study demonstrates a novel model system for fully 3D offline flexible mesh advection forced by velocities from structured grid models. The offline method is here described in detail and validated by assessing the errors of an analytical solution. Different case studies with passive tracers evaluated the model performance and effects of different computational meshes and time-steps. The method was shown to be accurate with a low error term for both mass balance and transformation of an analytical velocity field. The offline unstructured model yielded general distribution patterns of passive tracers comparable to the original structured grid tracer distribution. Further, it was demonstrated that the flow field can be interpolated to create a higher spatial resolution in the offline unstructured model although without additional information of flow patterns, which will enable high resolution modelling of e.g. nutrients and pollutants leaking from open water aquacultures or particle tracking. Hence, the method was shown suitable for future implementation of offline models in various areas including fjords, estuaries, coastal and open marine waters with any available hydrodynamic forcing.
