Abstract
Abstract. In this work, a multi-parameter inter-comparison of diverse ocean forecast models was conducted at the sea surface ranging from global to local scales in a two-phase stepwise strategy. Firstly, a comparison of CMEMS GLOBAL and the nested CMEMS IBI regional system was performed against satellite-derived and in situ observations. Results highlighted the overall benefits of both the GLOBAL direct data assimilation in open water and the increased horizontal resolution of IBI in coastal areas. Besides, IBI (Iberia–Biscay–Ireland) proved to capture shelf dynamics by better representing the horizontal extent and strength of a river freshwater plume, according to the results derived from the validation against in situ observations from a buoy moored in NW Spain. Secondly, a multi-model inter-comparison exercise for 2017 was performed in the Strait of Gibraltar among GLOBAL, IBI, and SAMPA (Sánchez-Garrido et al., 2013) high-resolution coastal forecast systems (partially nested to IBI) in order to elucidate the accuracy of each system to characterize the Atlantic Jet (AJ) inflow dynamics. A quantitative validation against hourly currents from high-frequency radar (HFR) highlighted both the steady improvement in AJ representation in terms of speed and direction when zooming from global to coastal scales through a multi-nesting model approach and also the relevance of a variety of factors at local scale such as a refined horizontal resolution, a tailored bathymetry, and a higher spatio-temporal resolution of the atmospheric forcing. The ability of each model to reproduce a 2 d quasi-permanent full reversal of the AJ surface inflow was examined in terms of wind-induced circulation patterns. SAMPA appeared to better reproduce the reversal events detected with HFR estimations, demonstrating the added value of imposing accurate meteorologically driven barotropic velocities in the open boundaries (imported from the NIVMAR (Álvarez-Fanjul et al., 2001) storm surge model) to take into account the remote effect of the atmospheric forcing over the entire Mediterranean basin, which was only partially included in IBI and GLOBAL systems. Finally, SAMPA coastal model outputs were also qualitatively analysed in the western Alboran Sea to put in a broader perspective the context of the onset, development, and end of such flow reversal episodes.
Highlights
Over the last three decades, significant progress has been made in the discipline of operational oceanography thanks to the substantial increase in high-performance computational resources that have fostered seamless evolution in ocean modelling techniques and numerical efficiency (Cotelo et al, 2018) and given rise to an inventory of operational ocean forecasting systems (OOFSs) running in overlapping regionsPublished by Copernicus Publications on behalf of the European Geosciences Union.P
In order to gain insight into the model skill assessment, the IBI service (IBISR) regional domain has been split into nine different subregions (Fig. 1a): the Irish Sea (IRISH), the English Channel (ECHAN), the Gulf of Biscay (GOBIS), the North Iberian Shelf (NIBSH), the West Iberian Shelf (WIBSH), the Western Mediterranean Sea (WSMED), the Gulf of Cádiz (CADIZ), the Strait of Gibraltar (GIBST), and the Canary Islands (ICANA)
In the two lateral open boundaries the model is partially forced by daily mean temperature, salinity, and velocity fields from Copernicus Marine Environment Monitoring Service (CMEMS) IBI regional model (Sotillo et al, 2015). Since such frequency is not suitable to resolve barotropic flows through the strait either (García-Lafuente et al, 2002b), tidal and meteorologically driven barotropic velocities are prescribed across the open boundaries: the former extracted from the Mog2D model described by Carrere and Lyard (2003) and the latter from the storm surge operational system developed by Álvarez-Fanjul et al (2001), which accounts for the remote effect of the atmospheric forcing in the barotropic flow through GIBST
Summary
Over the last three decades, significant progress has been made in the discipline of operational oceanography thanks to the substantial increase in high-performance computational resources that have fostered seamless evolution in ocean modelling techniques and numerical efficiency (Cotelo et al, 2018) and given rise to an inventory of operational ocean forecasting systems (OOFSs) running in overlapping regions. Small-scale ocean features must be explicitly computed and accurately reproduced by means of regional models with finer horizontal grid spacing but for a particular delimited area The success of this approach requires the seamless progress in several aspects, as previously identified by Wilkin et al (2017) and Kourafalou et al (2015): (i) a deep comprehension of the primary mechanisms driving coastal circulation, (ii) downscaling methods to adequately represent air–sea and land–sea interactions, and (iii) robust methods to embed high-resolution models in coarser-scale systems.
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