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

• Published in: Geoscientific Model Development
• Main Authors: Holt, J, Hyder, P, Ashworth, M, Harle, J, Hewitt, HT, Liu, H, New, AL, Pickles, S, Porter, A, Popova, E, Allen, JI, Siddorn, J, Wood, R
• Format: Article in Journal/Newspaper
• Language: English
• Published: European Geosciences Union 2017
• Subjects: North Atlantic
• Online Access: https://plymsea.ac.uk/id/eprint/8133/; https://plymsea.ac.uk/id/eprint/8133/1/gmd-10-499-2017.pdf; https://doi.org/10.5194/gmd-10-499-2017

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 < 500m 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 high-resolution model without tides. The benefits of resolution are particularly ...