Articles | Volume 21, issue 3 
            
                
                    
                    
                        
            
            
            https://doi.org/10.5194/npg-21-659-2014
                    © Author(s) 2014. This work is distributed under 
the Creative Commons Attribution 3.0 License.
                the Creative Commons Attribution 3.0 License.
Special issue:
                        
                    https://doi.org/10.5194/npg-21-659-2014
                    © Author(s) 2014. This work is distributed under 
the Creative Commons Attribution 3.0 License.
                the Creative Commons Attribution 3.0 License.
Assimilation of HF radar surface currents to optimize forcing in the northwestern Mediterranean Sea
J. Marmain
                                            Aix Marseille Université, CNRS/INSU, IRD, Mediterranean Institute of Oceanography (MIO),  UM 110, 13288 Marseille, France
                                        
                                    
                                            Université de Toulon, UMR7294, CNRS/INSU, IRD – Mediterranean Institute of Oceanography (MIO),  UM 110, 83957 La Garde, France
                                        
                                    A. Molcard
                                            Aix Marseille Université, CNRS/INSU, IRD, Mediterranean Institute of Oceanography (MIO),  UM 110, 13288 Marseille, France
                                        
                                    
                                            Université de Toulon, UMR7294, CNRS/INSU, IRD – Mediterranean Institute of Oceanography (MIO),  UM 110, 83957 La Garde, France
                                        
                                    P. Forget
                                            Aix Marseille Université, CNRS/INSU, IRD, Mediterranean Institute of Oceanography (MIO),  UM 110, 13288 Marseille, France
                                        
                                    
                                            Université de Toulon, UMR7294, CNRS/INSU, IRD – Mediterranean Institute of Oceanography (MIO),  UM 110, 83957 La Garde, France
                                        
                                    
                                            GeoHydrodynamics and Environment Research (GHER), AGO/MARE, Univeristy of Liège, Liège, Belgium
                                        
                                    Y. Ourmières
                                            Aix Marseille Université, CNRS/INSU, IRD, Mediterranean Institute of Oceanography (MIO),  UM 110, 13288 Marseille, France
                                        
                                    
                                            Université de Toulon, UMR7294, CNRS/INSU, IRD – Mediterranean Institute of Oceanography (MIO),  UM 110, 83957 La Garde, France
                                        
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Aida Alvera-Azcárate, Dimitry Van der Zande, Alexander Barth, Antoine Dille, Joppe Massant, and Jean-Marie Beckers
                                    Ocean Sci., 21, 787–805, https://doi.org/10.5194/os-21-787-2025, https://doi.org/10.5194/os-21-787-2025, 2025
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                                                This work presents an approach for increasing the spatial resolution of satellite data and interpolating gaps due to cloud cover, using a method called DINEOF (data-interpolating empirical orthogonal functions). The method is tested on turbidity and chlorophyll-a concentration data in the Belgian coastal zone and the North Sea. The results show that we are able to improve the spatial resolution of these data in order to perform analyses of spatial and temporal variability in coastal regions.
                                            
                                            
                                        Bayoumy Mohamed, Alexander Barth, Dimitry Van der Zande, and Aida Alvera-Azcárate
                                        EGUsphere, https://doi.org/10.5194/egusphere-2025-1578, https://doi.org/10.5194/egusphere-2025-1578, 2025
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                                                We quantified the role of climate change and internal variability on marine heatwaves (MHWs) in the North Sea over more than four decades (1982–2024). A key finding is the 2013 climate shift, which was associated with increased warming and MHWs. Long-term warming accounted for 80 % of the observed trend in MHW frequency. The most intense MHW event in May 2024 was attributed to an anomalous anticyclonic atmospheric circulation. We also explored the impact of MHWs on chlorophyll concentrations.
                                            
                                            
                                        Cécile Pujol, Alexander Barth, Iván Pérez-Santos, Pamela Muñoz-Linford, and Aida Alvera-Azcárate
                                        EGUsphere, https://doi.org/10.5194/egusphere-2025-1421, https://doi.org/10.5194/egusphere-2025-1421, 2025
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                                                Marine heatwaves and cold spells are periods of extreme sea temperatures. This study focuses on Chilean Northern Patagonia, a fjord region vulnerable due to its aquaculture. It aims to understand these events' distribution and identify the most affected basins. Results show higher intensity in enclosed areas like Reloncaví Sound and Puyuhuapi Fjord. Marine heatwaves are becoming more frequent over time, while cold spells are decreasing.
                                            
                                            
                                        Ehsan Mehdipour, Hongyan Xi, Alexander Barth, Aida Alvera-Azcárate, Adalbert Wilhelm, and Astrid Bracher
                                        EGUsphere, https://doi.org/10.5194/egusphere-2025-112, https://doi.org/10.5194/egusphere-2025-112, 2025
                                    This preprint is open for discussion and under review for Geoscientific Model Development (GMD). 
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                                                Phytoplankton are vital for marine ecosystems and nutrient cycling, detectable by optical satellites. Data gaps caused by clouds and other non-optimal conditions limit comprehensive analyses like trend monitoring. This study evaluated DINCAE and DINEOF gap-filling methods for reconstructing chlorophyll-a datasets, including total chlorophyll-a and five major phytoplankton groups. Both methods showed robust reconstruction capabilities, aiding pattern detection and long-term ocean colour analysis.
                                            
                                            
                                        Matjaž Zupančič Muc, Vitjan Zavrtanik, Alexander Barth, Aida Alvera-Azcarate, Matjaž Ličer, and Matej Kristan
                                        Geosci. Model Dev. Discuss., https://doi.org/10.5194/gmd-2024-208, https://doi.org/10.5194/gmd-2024-208, 2025
                                    Revised manuscript accepted for GMD 
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                                                Accurate sea surface temperature data (SST) is crucial for weather forecasting and climate modeling, but satellite observations are often incomplete. We developed a new method called CRITER, which uses machine learning to fill in the gaps in SST data. Our two-stage approach reconstructs large-scale patterns and refines details. Tested on Mediterranean, Adriatic, and Atlantic seas data, CRITER outperforms current methods, reducing errors by up to 44 %.
                                            
                                            
                                        Alexander Barth, Julien Brajard, Aida Alvera-Azcárate, Bayoumy Mohamed, Charles Troupin, and Jean-Marie Beckers
                                    Ocean Sci., 20, 1567–1584, https://doi.org/10.5194/os-20-1567-2024, https://doi.org/10.5194/os-20-1567-2024, 2024
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                                                Most satellite observations have gaps, for example, due to clouds. This paper presents a method to reconstruct missing data in satellite observations of the chlorophyll a concentration in the Black Sea. Rather than giving a single possible reconstructed field, the discussed method provides an ensemble of possible reconstructions using a generative neural network. The resulting ensemble is validated using techniques from numerical weather prediction and ocean modelling.
                                            
                                            
                                        Francesca Doglioni, Robert Ricker, Benjamin Rabe, Alexander Barth, Charles Troupin, and Torsten Kanzow
                                    Earth Syst. Sci. Data, 15, 225–263, https://doi.org/10.5194/essd-15-225-2023, https://doi.org/10.5194/essd-15-225-2023, 2023
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                                                This paper presents a new satellite-derived gridded dataset, including 10 years of sea surface height and geostrophic velocity at monthly resolution, over the Arctic ice-covered and ice-free regions, up to 88° N. We assess the dataset by comparison to independent satellite and mooring data. Results correlate well with independent satellite data at monthly timescales, and the geostrophic velocity fields can resolve seasonal to interannual variability of boundary currents wider than about 50 km.
                                            
                                            
                                        Alexander Barth, Aida Alvera-Azcárate, Charles Troupin, and Jean-Marie Beckers
                                    Geosci. Model Dev., 15, 2183–2196, https://doi.org/10.5194/gmd-15-2183-2022, https://doi.org/10.5194/gmd-15-2183-2022, 2022
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                                                Earth-observing satellites provide routine measurement of several ocean parameters. However, these datasets have a significant amount of missing data due to the presence of clouds or other limitations of the employed sensors. This paper describes a method to infer the value of the missing satellite data based on a convolutional autoencoder (a specific type of neural network architecture). The technique also provides a reliable error estimate of the interpolated value.
                                            
                                            
                                        Malek Belgacem, Katrin Schroeder, Alexander Barth, Charles Troupin, Bruno Pavoni, Patrick Raimbault, Nicole Garcia, Mireno Borghini, and Jacopo Chiggiato
                                    Earth Syst. Sci. Data, 13, 5915–5949, https://doi.org/10.5194/essd-13-5915-2021, https://doi.org/10.5194/essd-13-5915-2021, 2021
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                                                The Mediterranean Sea exhibits an anti-estuarine circulation, responsible for its low productivity. Understanding this peculiar character is still a challenge since there is no exact quantification of nutrient sinks and sources. Because nutrient in situ observations are generally infrequent and scattered in space and time, climatological mapping is often applied to sparse data in order to understand the biogeochemical state of the ocean. The dataset presented here partly addresses these issues.
                                            
                                            
                                        Alexander Barth, Aida Alvera-Azcárate, Matjaz Licer, and Jean-Marie Beckers
                                    Geosci. Model Dev., 13, 1609–1622, https://doi.org/10.5194/gmd-13-1609-2020, https://doi.org/10.5194/gmd-13-1609-2020, 2020
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                                                DINCAE is a method for reconstructing missing data in satellite datasets using a neural network. Satellite observations working in the optical and infrared bands are affected by clouds, which obscure part of the ocean underneath. In this paper, a neural network with the structure of a convolutional auto-encoder is developed to reconstruct the missing data based on the available cloud-free pixels in satellite images.
                                            
                                            
                                        Luc Vandenbulcke and Alexander Barth
                                    Ocean Sci., 15, 291–305, https://doi.org/10.5194/os-15-291-2019, https://doi.org/10.5194/os-15-291-2019, 2019
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                                                In operational oceanography, regional and local models use large-scale models (such as those run by CMEMS) for their initial and/or boundary conditions, but unfortunately there is no feedback that improves the large-scale models. The present study aims at replacing normal two-way nesting by a data assimilation technique. This 
                                            
                                        upscalingmethod is tried out in the north-western Mediterranean Sea using the NEMO model and shows that the basin-scale model does indeed benefit from the nested model.
J.-M. Beckers, A. Barth, I. Tomazic, and A. Alvera-Azcárate
                                    Ocean Sci., 10, 845–862, https://doi.org/10.5194/os-10-845-2014, https://doi.org/10.5194/os-10-845-2014, 2014
                            A. Barth, J.-M. Beckers, C. Troupin, A. Alvera-Azcárate, and L. Vandenbulcke
                                    Geosci. Model Dev., 7, 225–241, https://doi.org/10.5194/gmd-7-225-2014, https://doi.org/10.5194/gmd-7-225-2014, 2014
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