Abstract
The Unresolved Obstacles Source Term (UOST) is a general methodology for parameterizing the dissipative effects of subscale islands, cliffs, and other unresolved features in ocean wave models. Since it separates the dissipation from the energy advection scheme, it can be applied to any numerical scheme or any type of mesh. UOST is now part of the official release of WAVEWATCH III, and the freely available package alphaBetaLab automates the estimation of the parameters needed for the obstructed cells. In this contribution, an assessment of global regular and unstructured (triangular) wave models employing UOST is presented. The results in regular meshes show an improvement in model skill, both in terms of spectrum and of integrated parameters, thanks to the UOST modulation of the dissipation with wave direction, and to considering the cell geometry. The improvement is clear in wide areas characterized by the presence of islands, like the whole central-western Pacific Basin. In unstructured meshes, the use of UOST removes the need of high resolution in proximity of all small features, leading to (a) a simplification in the development process of large scale and global meshes, and (b) a significant decrease of the computational demand of accurate large-scale models.
Highlights
This article is part of the Topical Collection on the 16th International Workshop on Wave Hindcasting and Forecasting in Melbourne, AU, November 10-15, 2019Responsible Editor: Jenny M BrownElectronic supplementary material The online version of this article contains supplementary material, which is available to authorized users.Ferrara, Via Saragat, 1, 44122 Ferrara, Italy 3 Department of Earth Sciences, University of Cádiz, Avda
The results are similar for the simulations with the 0.4° regular mesh and on the unstructured mesh, though with biases of Hs reduced with respect to NOSM-150
For NOSM-040 (NOSM-UNST), the overall overestimation of Hs is 5.3% (2.6%), with local exceedance beyond 20% in many areas (Figs. 2a and 3a). Both GRIDGEN and Unresolved Obstacles Source Term (UOST) reduce such kind of overestimation, but at 0.4° as at 1.5° GRIDGEN comes with an underestimation of Hs in the western Pacific Basin and in other areas filled with islands (Fig. 2b)
Summary
This article is part of the Topical Collection on the 16th International Workshop on Wave Hindcasting and Forecasting in Melbourne, AU, November 10-15, 2019. The dissipative effect of unresolved islands and small obstacles is a major source of error in wave models if neglected, both locally and on large scale. Hardy and Young (1996) and Hardy et al (2000) showed the advantages of modulating the attenuation with wave direction, as small islands with irregular and elongated shape can lead to a non-isotropic dissipation of energy. The approach they proposed, which is based on the advection scheme and.
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