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  • 1
    Publication Date: 2017-01-04
    Description: A two-dimensional, high-resolution, non-linear, two-layer, free-surface, boundary-fitted co-ordinate, hydrostatic model was applied to study the time–space variability of hydraulic controls and the development of internal bores in the Strait of Gibraltar. The model predicts the occurrence of four averaged (over a tropical month) controls located to the west of the Spartel Sill, at the Spartel and Camarinal Sills and in the Tarifa Narrows. The last of these controls is apparent in the sense that it consists of discrete fragments alternating with subcritical flow regions. The only control which extends over the whole width of the strait is the control at the Camarinal Sill, but it breaks down during neap tide, too. This control exists concurrently with the control in the Tarifa Narrows for short periods, while for much of the tropical month there is either just one or neither of the controls. The model predicts the development of a hydraulic jump and a jump-drop pair near the Camarinal Sill; the appearance of bulges of Mediterranean water to the east and west of the sill; the large-amplitude and small-amplitude internal bores released from the Camarinal Sill, which travel, respectively, eastward and westward, and their transformation due to radial spreading and dissipative effects. Also presented here are the results illustrating the effects of earth's rotation on the internal bores in the Strait of Gibraltar.
    Type: Article , PeerReviewed
    Format: text
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  • 2
    Publication Date: 2020-07-06
    Description: Climate simulations for the North Atlantic and Europe for recent and future conditions simulated with the regionally coupled ROM model are analyzed and compared to the results from the MPI‐ESM. The ROM simulations also include a biogeochemistry and ocean tides. For recent climate conditions, ROM generally improves the simulations compared to the driving model MPI‐ESM. Reduced oceanic biases in the Northern Atlantic are found, as well as a better simulation of the atmospheric circulation, notably storm tracks and blocking. Regarding future climate projections for the 21st century following the RCP 4.5 and 8.5 scenarios, MPI‐ESM and ROM largely agree qualitatively on the climate change signal over Europe. However, many important differences are identified. For example, ROM shows an SST cooling in the Subpolar Gyre which is not present in MPI‐ESM. Under the RCP8.5 scenario, ROM Arctic sea ice cover is thinner and reaches the seasonally ice‐free state by 2055, well before MPI‐ESM. This shows the decisive importance of higher ocean resolution and regional coupling for determining the regional responses to global warming trends. Regarding biogeochemistry, both ROM and MPI‐ESM simulate a widespread decline in winter nutrient concentration in the North Atlantic of up to ~35%. On the other hand, the phytoplankton spring bloom in the Arctic and in the North‐Western Atlantic starts earlier and the yearly primary production is enhanced in the Arctic in the late 21st century. These results clearly demonstrate the added value of ROM to determine more detailed and more reliable climate projections at the regional scale.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 3
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    COPERNICUS GESELLSCHAFT MBH
    In:  EPIC3Ocean Science, COPERNICUS GESELLSCHAFT MBH, 16(3), pp. 743-765, ISSN: 1812-0792
    Publication Date: 2020-07-06
    Description: We analyze the climate change signal in the Mediterranean Sea using the regionally coupled model REMO–OASIS–MPIOM (ROM; abbreviated from the regional atmosphere model, the OASIS3 coupler and the Max Planck Institute Ocean Model). The ROM oceanic component is global with regionally high horizontal resolution in the Mediterranean Sea so that the water exchanges with the adjacent North Atlantic and Black Sea are explicitly simulated. Simulations forced by ERA-Interim show an accurate representation of the present Mediterranean climate. Our analysis of the RCP8.5 (representative concentration pathway) scenario using the Max Planck Institute Earth System Model shows that the Mediterranean waters will be warmer and saltier throughout most of the basin by the end of this century. In the upper ocean layer, temperature is projected to have a mean increase of 2.7 ∘C, while the mean salinity will increase by 0.2 psu, presenting a decreasing trend in the western Mediterranean in contrast to the rest of the basin. The warming initially takes place at the surface and propagates gradually to deeper layers. Hydrographic changes have an impact on intermediate water characteristics, potentially affecting the Mediterranean thermohaline circulation in the future.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 4
    Publication Date: 2021-07-26
    Description: The Canary current upwelling is one of the major eastern boundary coastal upwelling systems in the world, bearing a high productive ecosystem and commercially important fisheries. The Canary current upwelling system (CCUS) has a large latitudinal extension, usually divided into upwelling zones with different characteristics. Eddies, filaments and other mesoscale processes are known to have an impact in the upwelling productivity, thus for a proper representation of the CCUS and high horizontal resolution are required. Here we assess the CCUS present climate in the atmosphere–ocean regionally coupled model. The regional coupled model presents a global oceanic component with increased horizontal resolution along the northwestern African coast, and its performance over the CCUS is assessed against relevant reanalysis data sets and compared with an ensemble of global climate models (GCMs) and an ensemble of atmosphere-only regional climate models (RCMs) in order to assess the role of the horizontal resolution. The coupled system reproduces the larger scale pattern of the CCUS and its latitudinal and seasonal variability over the coastal band, improving the GCMs outputs. Moreover, it shows a performance comparable to the ensemble of RCMs in representing the coastal wind stress and near-surface air temperature fields, showing the impact of the higher resolution and coupling for CCUS climate modelling. The model is able of properly reproducing mesoscale structures, being able to simulate the upwelling filaments events off Cape Ghir, which are not well represented in most of GCMs. Our results stress the ability of the regionally coupled model to reproduce the larger scale as well as mesoscale processes over the CCUS, opening the possibility to evaluate the climate change signal there with increased confidence.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 5
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    In:  EPIC3Fundamentalnaya i prikladnaya gidrofizika, 9(4), pp. 15-24, ISSN: 2073-6673
    Publication Date: 2017-01-27
    Description: We make a review on the modelling efforts devoted to better understand the complex oceanography of the Strait of Gibraltar, where Atlantic waters enter the Mediterranean Sea as a surface flow, and Mediterranean outflowing waters spread into the interior of the North Atlantic forming a prominent basin-scale termohaline anomaly at mid-depths. Besides the mean exchange flows relevant phenomena include tides, high amplitude internal waves, meteorologically forced subinertial oscillations, mixing, and involve a wide-range of spatio-temporal scales. The remarkable progress achieved in understanding and modelling the ocean processes in the Strait of Gibraltar allows now undertaking new societal demands and scientific challenges. One societal demand is given by the increasing need of operational oceanographic information as a support tool for decision-makers in an area considered as one of world's busiest shipping lanes, with an increased risk of maritime accidents and environmental pollution. We present an Operational Oceanography system for the Strait of Gibraltar responding to that demand. On the other hand, new scientific challenges call for the need of developing perspective-modelling studies accounting for process and scale interactions. Using a global ocean general circulation model with regional high resolution around the Iberian Peninsula we are able to resolve the local-scale at the Strait of Gibraltar and the Gulf of Cádiz while focusing on the basin scale. As a result, we find that tidally-induced local-scale processes in the Strait and in the Gulf of Cádiz appear to have a drastic impact on the distribution of Mediterranean outflow waters in the Atlantic basin.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , peerRev
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  • 6
    Publication Date: 2016-09-19
    Description: The key role of the South Atlantic Anticyclone (SAA) on the seasonal cycle of the tropical Atlantic is investigated with a regionally coupled atmosphere–ocean model for two different coupled domains. Both domains include the equatorial Atlantic and a large portion of the northern tropical Atlantic, but one extends southward, and the other northwestward. The SAA is simulated as internal model variability in the former, and is prescribed as external forcing in the latter. In the first case, the model shows significant warm biases in sea surface temperature (SST) in the Angola-Benguela front zone. If the SAA is externally prescribed, these biases are substantially reduced. The biases are both of oceanic and atmospheric origin, and are influenced by ocean–atmosphere interactions in coupled runs. The strong SST austral summer biases are associated with a weaker SAA, which weakens the winds over the southeastern tropical Atlantic, deepens the thermocline and prevents the local coastal upwelling of colder water. The biases in the basins interior in this season could be related to the advection and eddy transport of the coastal warm anomalies. In winter, the deeper thermocline and atmospheric fluxes are probably the main biases sources. Biases in incoming solar radiation and thus cloudiness seem to be a secondary effect only observed in austral winter. We conclude that the external prescription of the SAA south of 20°S improves the simulation of the seasonal cycle over the tropical Atlantic, revealing the fundamental role of this anticyclone in shaping the climate over this region.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 7
    Publication Date: 2015-02-17
    Description: The general circulation models used to simulate global climate typically feature resolution too coarse to reproduce many smaller scale processes, which are crucial to determining the regional responses to climate change. A novel approach to downscale climate change scenarios is presented which includes the interactions between the North Atlantic Ocean and the European shelves as well as their impact on the North Atlantic and European climate. The goal of this paper is to introduce the global ocean – regional atmosphere coupling concept and to show the potential benefits of this model system to simulate present day climate. A global ocean – sea ice – marine biogeochemistry model (MPIOM/HAMOCC) with regionally high horizontal resolution is coupled to an atmospheric regional model (REMO) and global terrestrial hydrology model (HD) via the OASIS coupler. Moreover, results obtained with ROM using NCEP/NCAR reanalysis and ECHAM5/MPIOM CMIP3 historical simulations as boundary conditions are presented and discussed for the North Atlantic and North European region. The validation of all the model components, i.e. ocean, atmosphere, terrestrial hydrology and ocean biogeochemistry is performed and discussed. The careful and detailed validation of ROM provides evidence that the proposed model system improves the simulation of many aspects of the regional climate, remarkably the ocean, even though some biases persist in other model components, thus leaving potential for future improvement. We conclude that ROM is a powerful tool to estimate possible impacts of climate change on the regional scale.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 8
    Publication Date: 2022-05-01
    Description: Deep water formation (DWF) in the North Western Mediterranean (NWMed) is a key feature of Mediterranean overturning circulation. DWF changes under global warming may have an impact on the Mediterranean biogeochemistry and marine ecosystem. Here we analyze the deep convection in the Gulf of Lions (GoL) in a changing climate using a regional climate system model with a horizontal resolution high enough to represent DWF. We find that under the RCP8.5 scenario the NWMed DWF collapses by 2040–2050, leading to a 92% shoaling in the winter mixed layer by the end of the century. The collapse is related to a strengthening of the vertical stratification in the GoL caused by changes in properties of Modified Atlantic Water and Levantine Intermediate Water, being their relative contribution to the increase of the stratification 57.8% and 42.2%, respectively. The stratification changes also alter the Mediterranean overturning circulation and the exchange with the Atlantic.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 9
    Publication Date: 2022-05-01
    Description: The Tyrrhenian Sea plays an important role in the winter deep water formation in the northwestern Mediterranean through the water that enters the Ligurian Sea via the Corsica Channel. Therefore, the study of the impact of the changes on the future climate on the Tyrrhenian circulation and its consequences represents an important issue. Furthermore, the seasonally dependent Tyrrhenian circulation, which is rich in dynamical mesoscale structures, is dominated by the interplay of local climate and the basin-wide Mediterranean circulation via the water transport across its major straits, and an adequate representation of its features represents an important modeling challenge. In this work we examine with a regionally coupled atmosphere–ocean model the changes in the Tyrrhenian circulation by the end of the 21st century under the RCP8.5 emission scenario, their driving mechanisms, and their possible impact on winter convection in the NW Mediterranean. Our model successfully reproduces the main features of the Mediterranean Sea and Tyrrhenian Basin present-day circulation. We find that toward the end of the century the winter cyclonic along-slope stream around the Tyrrhenian Basin becomes weaker. This weakening increases the wind work transferred to the mesoscale structures, which become more intense than at present in winter and summer. We also find that, in the future, the northward water transport across the Corsica Channel towards the Liguro-Provençal basin becomes smaller than today. Also, water that flows through this channel presents a stronger stratification because of a generalized warming with a freshening of upper and a saltening of intermediate waters. Both factors may contribute to the interruption of deep water formation in the Gulf of Lions by the end of the century.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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