Articles

Els filtres actuals son: Any inici = 2023, Any final = 2024
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Talone M., Zibordi G., Pitarch J., (2024)
IEEE Geoscience and Remote Sensing Letters, 21, 6002105. DOI: 10.1109/LGRS.2024.3350928. (BibTeX: talone.etal.2024)
Resum: Veure
The potential for applying in situ multispectral Rrs data from the Ocean Color component of the Aerosol Robotic Network (AERONET-OC) to validate satellite-derived ocean color hyperspectral Rrs products was investigated in the 400–700 nm interval. The analysis was performed using a comprehensive dataset of simulated hyperspectral Rrs in combination with an algorithm designed to reconstruct hyperspectral Rrs from multispectral ones. Results were assessed using in situ hyperspectral Rrs representative of diverse water types. Excluding waters dominated by a high concentration of colored dissolved organic matter, results indicate the capability of determining hyperspectral Rrs from AERONET-OC multispectral data with mean relative and absolute uncertainties generally lower than 2% and 5×10−5 sr−1, respectively, at a number of the key center-wavelengths of the Ocean Color Instrument (OCI) onboard the Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) spacecraft.
Paraules clau: Ocean color, remote sensing, validation.
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Umbert M., De Andrés E., Sánchez M., Gabarró C., Hoareau N., González-Gambau V., García-Espriu A., Olmedo E., P. Raj R., Xie J., Catany R. (2024)
Ocean Science, 20, 279-291. DOI: 10.5194/os-20-279-2024. (BibTeX: umbert.etal.2024a)
Resum: Veure
The hydrography of the Arctic Ocean has expe- rienced profound changes over the last 2 decades. The sea ice extent has declined by more than 10 % per decade, and its liquid freshwater content has increased mainly due to glaciers and sea ice melting. Further, new satellite retrievals of sea surface salinity (SSS) in the Arctic might contribute to better characterizing the freshwater changes in cold re- gions. Ocean salinity and freshwater content are intimately related such that an increase (decrease) in one entails a de- crease (increase) in the other. In this work, we evaluate the freshwater content in the Beaufort Gyre using surface salin- ity measurements from the satellite radiometric mission Soil Moisture and Ocean Salinity (SMOS) and TOPAZ4b reanal- ysis salinity at depth, estimating the freshwater content from 2011 to 2019 and validating the results with in situ mea- surements. The results highlight the underestimation of the freshwater content using reanalysis data in the Beaufort Sea and a clear improvement in the freshwater content estimation when adding satellite sea surface salinity measurements in the mixed layer. The improvements are significant, with up to a 70 % reduction in bias in areas near the ice melting. Our re- search demonstrates how remotely sensed salinity can assist us in better monitoring the changes in the Arctic freshwater content and understanding key processes related to salinity variations that cause density differences with potential to in- fluence the global circulation system that regulates Earth’s climate
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Roca Ramis de Ayreflor P., Viudez A. (2023)
European Journal of Mechanics B/Fluids, 103, 329-333. DOI: 0.1016/j.euromechflu.2023.10.009. (BibTeX: rocaramisdeayreflor.viudez.2023)
Resum: Veure
Inelastic interactions between a small, intense dipole and a weak, neutral monopole in two-dimensional flows are analysed. The neutral vortex has vanishing exterior potential flow and the interactions involve the rotational flow of the vortices. It is shown that dipoles of small-size but large-amplitude, relative to the neutral vortex, may cross the vortex and scatter while leave the vortex stable
Paraules clau: Inelastic interactions, Lamb–Chaplygin dipole, Neutral vortex
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Caetano L., Guallar C., Martín J., Vidal M., Cotrim da Cunha L., Vieira R., Amora-Nogueira L., Pelegrí J.L., Marotta H. (2023)
Journal of Marine Systems, 239 DOI: 10.1016/j.jmarsys.2023.103858. (BibTeX: caetano.etal.2023)
Resum: Veure
Subpolar coastal waters are key hotspots in the global carbon cycle. However, the small-scale distribution of partial pressure of carbon dioxide (pCO2) in these environments and the physical and biological controls underlying this variability are still poorly understood. Here, we examine simultaneous high-resolution spatial measurements of wind speed and pCO2, temperature, salinity, and in-vivo chlorophyll-a fluorescence (chl-a fluo, a proxy of phytoplankton biomass) in surface waters that were obtained during an oceanographic survey in the Argentinian Beagle Channel (subantarctic Atlantic Patagonian) in early fall 2017. The 240 km study transect (centered at 55◦S - 67◦W) was divided into two zones: (A1) The Beagle Channel innermost portion, semi-enclosed and subject to strong continental influence and (A2) its eastern outlet towards the open Southwest Atlantic. Discrete seawater samples were also collected for apparent oxygen utilization (AOU), nutrients and pH measurements. High-resolution spatial measurements revealed the persistence of pCO2 below atmospheric equilibrium, increasing in median (interquartile range 25–75%) from 314 μatm in the inner Beagle Channel (A1) to 348 μatm towards the adjacent open sea (A2). A decrease in atmospheric CO2 sequestration was associated with an increase in water temperature from 9.5 ◦C to 10.7 ◦C, salinity from 30.8 to 32.5, and chl-a fluo from 2.24 to 2.91 mg m− 3 along the coastal-offshore gradient. Low AOU and nutrient levels were found in regions inside the channel. Indeed, the relationships between CO2 and temperature or salinity were significantly different from those expected from the theoretical solubility effect, indicating a dominance of metabolic over physicochemical controls on this gas. Moreover, physical factors such as vertical stratification contributed to the variable surface pCO2 values. These findings reveal the existence of short-scale spatial variability of CO2 in the Beagle Channel, improving our understanding of the multiple controls on atmospheric carbon sequestration in extensive subpolar continental shelves.
Paraules clau: pCO2 High-resolution spatial variability Patagonia Sub-Antarctic waters Beagle Channel
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Estrada-Allis S.N., Rodríguez-Santana A., Naveira-Garabato A.C., García-Weil L., Arcos-Pulido M., Emelianov M. (2023)
Frontiers in Marine Science, 10 DOI: 10.3389/fmars.2023.1113879. (BibTeX: estrada-allis.etal.2023)
Resum: Veure
The filaments of the African Eastern Boundary Upwelling System (EBUS) are responsible for feeding nutrients to the oligotrophic waters of the northeastern Atlantic. However, turbulent mixing associated with nutrient uplift in filaments is poorlydocumented and has beenmainly evaluatednumerically. Usingmicrostructure profiler measurements, we detected enhanced turbulent kinetic energy dissipation rates (e) within the Cape Ghir upwelling filament. In contrast to previous studies, this enhancement was not related to symmetrical instabilities induced by down-front winds but to an increase in vertical current shear at the base of the mixed layer (hr). In order to quantify the impact of vertical shear and the influence of the active mixing layer depth (he ) in the filament, a simple one-dimensional (1D) turbulent entrainment approachwas used.We found that the effect of turbulent enhancement, togetherwith the isopycnal morphology of the filament front, drove the formation of local positive entrainment zones (Dh = he − hr), as he was deeper than hr. This provided suitable conditions for the entrainment of cold, nutrient-rich waters from below the filament pycnocline and the upward transport of biophysical properties to the upper boundary layer of the front.We also found that diapycnal nutrient fluxes in stations influenced by the filament (1.35 mmol m-2 d-1) were two orders of magnitude higher than those of stations not affected by the filament front (0.02 mmol m-2 d-1). Despite their importance, the effects of vertical shear and he have often been neglected in entrainment parameterizations. Thus, a modified entrainment parameterization was adapted to include vertical shear and observed e, which are overestimated by existing parameterizations. To account for the possible role of internal waves in the generation of vertical shear, we considered internal wave scaling to parameterize the observed dissipation. Using this adapted parameterization, the average entrainment velocities were six times (6 m d-1) higher than those obtained with the classic parameterization (1 m d-1).
Paraules clau: upwelling filament, diapycnal mixing, active mixing, turbulent, entrainment, entrainment parameterization
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Fournier S., Bingham F.M., González-Haro C., Hayashi A., Ulfsax-Carlin K.M., Brodnitz S.K., González-Gambau V., Kuusela M. (2023)
Remote Sensing, 15, 422 DOI: 10.3390/rs15020422. (BibTeX: fournier.etal.2023)
Resum: Veure
Evaluating and validating satellite sea surface salinity (SSS) measurements is fundamental. There are two types of errors in satellite SSS: measurement error due to the instrument’s inaccuracy and problems in retrieval, and sampling error due to unrepresentativeness in the way that the sea surface is sampled in time and space by the instrument. In this study, we focus on sampling errors, which impact both satellite and in situ products. We estimate the sampling errors of Level 3 satellite SSS products from Aquarius, SMOS and SMAP, and in situ gridded products. To do that, we use simulated L2 and L3 Aquarius, SMAP and SMOS SSS data, individual Argo observations and gridded Argo products derived from a 12-month high-resolution 1/48◦ ocean model. The use of the simulated data allows us to quantify the sampling error and eliminate the measurement error. We found that the sampling errors are high in regions of high SSS variability and are globally about 0.02/0.03 psu at weekly time scales and 0.01/0.02 psu at monthly time scales for satellite products. The in situ-based product sampling error is significantly higher than that of the three satellite products at monthly scales (0.085 psu) indicating the need to be cautious when using in situ-based gridded products to validate satellite products. Similar results are found using a Correlated Triple Collocation method that quantifies the standard deviation of products’ errors acquired with different instruments. By improving our understanding and quantifying the effect of sampling errors on satellite-in situ SSS consistency over various spatial and temporal scales, this study will help to improve the validation of SSS, the robustness of scientific applications and the design of future salinity missions.
Paraules clau: sea surface salinity; SMAP; SMOS; Aquarius; sampling errors
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Gabarró C., Hughes N., Wilkinson J., Bertino L., Bracher A., Diehl T., Dierking W., Gonzalez-Gambau V., Lavergne T., Madurell T., Malnes E., Mae Wagner P. (2023)
Frontiers in Remote Sensing, 4 DOI: 10.3389/frsen.2023.952091. (BibTeX: gabarro.etal.2023)
Resum: Veure
Improving satellite-based monitoring of the polar regions: Identification of research and capacity gaps Carolina Gabarró 1 *, Nick Hughes 2 , Jeremy Wilkinson 3 , Laurent Bertino 4 , Astrid Bracher 5 , 6 , Thomas Diehl 7 , Wolfgang Dierking 8 ,5 , Veronica Gonzalez-Gambau 1 , Thomas Lavergne 9 , Teresa Madurell 1 , Eirik Malnes 10 and Penelope Mae Wagner 2 1 Barcelona Expert Center (BEC) and Institute of Marine Sciences (ICM), Consejo Superior de Investigaciones Marinas (CSIC), Barcelona, Spain, 2 Norwegian Meteorological Institute, Norwegian Ice Service, Tromsø, Norway, 3 British Antarctic Survey, Cambridge, United Kingdom, 4 Nansen Environmental and Remote Sensing Center and Bjerknes Centre for Climate Research, NERSC, Bergen, Norway, 5 Alfred- Wegener-Institute Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany, 6 Institute of Environmental Physics, University Bremen, Bremen, Germany, 7 European Commission, Joint Research Centre, Ispra, Italy, 8 UiT The Arctic University of Norway, Tromsø, Norway, 9 Research and Development Department, Norwegian Meteorological Institute, Oslo, Norway, 10 NORCE Norwegian Research Centre AS, Oslo, Norway We present a comprehensive review of the current status of remotely sensed and in situ sea ice, ocean, and land parameters acquired over the Arctic and Antarctic and identify current data gaps through comparison with the portfolio of products provided by Copernicus services. While we include several land parameters, the focus of our review is on the marine sector. The analysis is facilitated by the outputs of the KEPLER H2020 project. This project developed a road map for Copernicus to deliver an improved European capacity for monitoring and forecasting of the Polar Regions, including recommendations and lessons learnt, and the role citizen science can play in supporting Copernicus’ capabilities and giving users ownership in the system. In addition to summarising this information we also provide an assessment of future satellite missions (in particular the Copernicus Sentinel Expansion Missions), in terms of the potential enhancements they can provide for environmental monitoring and integration/assimilation into modelling/forecast products. We identify possible synergies between parameters obtained from different satellite missions to increase the information content and the robustness of specific data products considering the end-users requirements, in particular maritime safety. We analyse the potential of new variables and new techniques relevant for assimilation into simulations and forecasts of environmental conditions and changes in the Polar Regions at various spatial and temporal scales. This work concludes with several specific recommendations to the EU for improving the satellite-based monitoring of the Polar Regions
Paraules clau: polar observations, satellite remote sensing, Copernicus, citizen science, Arctic, recommendation for stakeholders
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Grégoire M., Alvera-Azcaráte A., Buga L., Capet A., Constantin S., D\'ortenzio F., Doxaran D., Faugeras Y., García-Espriu A., Golumbeanu M., González-Haro C., González-Gambau V., Kasprzyk J.P., Ivanov E., , , Mateescu R., Meulders C., Olmedo E., Pons L., Pujol M.I., Sarbu G., Turiel A., Vandenbulcke L., Rio M.H. (2023)
Frontiers in Marine Science, 9, 2862 DOI: 10.3389/fmars.2022.998970. (BibTeX: gregoire.etal.2023)
Resum: Veure
In this paper, satellite products developed during the Earth Observation for Science and Innovation in the Black Sea (EO4SIBS) ESA project are presented. Ocean colour, sea level anomaly and sea surface salinity datasets are produced for the last decade and validated with regional in-situ observations. New data processing is tested to appropriately tackle the Black Sea’s particular configuration and geophysical characteristics. For altimetry, the full rate (20Hz) altimeter measurements from Cryosat-2 and Sentinel-3A are processed to deliver a 5Hz along-track product. This product is combined with existing 1Hz product to produce gridded datasets for the sea level anomaly, mean dynamic topography, geostrophic currents. This new set of altimetry gridded products offers a better definition of the main Black Sea current, a more accurate reconstruction and characterization of eddies structure, in particular, in coastal areas, and improves the observable wavelength by a factor of 1.6. The EO4SIBS sea surface salinity from SMOS is the first satellite product for salinity in the Black Sea. Specific data treatments are applied to remedy the issue of land-sea and radio frequency nterference contamination and to adapt the dielectric constant model to the low salinity and cold waters of the Black Sea. The quality of the SMOS products is assessed and shows a significant improvement from Level-2 to Level -3 and Level 4 products. Level-4 products accuracy is 0.4-0.6 psu, a comparable value to that in the Mediterranean Sea. On average SMOS sea surface salinity is lower than salinity measured by Argo floats, with a larger error in the eastern basin. The adequacy of SMOS SSS to reproduce the spatial characteristics of the Black Sea surface salinity and, in particular, plume patterns is analyzed. For ocean colour, chlorophyll-a, turbidity and suspended particulate materials are proposed using regional calibrated algorithms and satellite data provided by OLCI sensor onboard Sentinel-3 mission. The seasonal cycle of ocean colour products is described and a water classification scheme is proposed. The development of these three types of products has suffered from important in-situ data gaps that hinder a sound calibration of the algorithms and a proper assessment of the datasets quality. We propose recommendations for improving the in-situ observing system that will support the development of satellite products.
Paraules clau: satellite, ocean colour, altimetry, salinity, Black Sea, environment monitoring, observing system
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Martínez J., Leonelli F.E., García-Ladona E., Garrabou J., Kersting D.K., Bensoussan N., Pisano A. (2023)
Frontiers in Marine Science, 10 DOI: 10.3389/fmars.2023.1193164. (BibTeX: martinez.etal.2023)
Resum: Veure
Anomalous warming of the upper ocean is increasingly being observed in the Mediterranean Sea. Extreme events, known as marine heatwaves (MHWs), can have a profound impact on marine ecosystems, and their correct detection and characterization are crucial to define future impact scenarios. Here, we analyze MHWs observed over the last 41 years (1982–2022) in the Mediterranean sea surface temperatures (SSTs). We show that the intensification in frequency, intensity, and duration of Mediterranean MHWs in recent years is mainly due to a shift in SST mean that occurred in the last two decades and largely reduced when analyzing detrended SST data. Detrending thus allows the use of a fixed climatology without overestimating MHW properties over time and distinguishes long-term warming (i.e., trend) from transient and abrupt SST changes. Analogous results are also found over a shorter temporal period, by analyzing 13 years (2007–2020) of in situ data collected at different depths (5 to 40 m) at Columbretes Islands. Additionally, the in situ analysis reveals that atmospheric summer heatwaves could affect a layer of 10 m in depth. Lastly, a catalogue of the major Mediterranean MHWs that have occurred since 1982 is presented. This catalogue evidences an exceptionally long-lasting and intense MHW, starting in May 2022 and persisting, at least, until the end of the year, resulting in the event with the highest cumulative intensity just after the well-known 2003 MHW event.
Paraules clau: marine heatwaves, Mediterranean Sea, sea surface temperature, extreme events, climate change, warming seas
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Martin-Rey M., Valles-Casanova I., Pelegrí J.L. (2023)
Journal of Climate, 36, 2625-2643. DOI: 10.1175/JCLI-D-22-0184.1. (BibTeX: martin-rey.etal.2023)
Resum: Veure
The impact of tropical Atlantic Ocean variability modes in the variability of the upper-ocean circulation has been investigated. For this purpose, we use three oceanic reanalyses, an interannual forced-ocean simulation, and satellite data for the period 1982–2018. We have explored the changes in the main surface and subsurface ocean currents during the emergence of Atlantic meridional mode (AMM), Atlantic zonal mode (AZM), and AMM–AZM connection. The developing phase of the AMM is associated with a boreal spring intensification of North Equatorial Countercurrent (NECC) and a reinforced summer Eastern Equatorial Undercurrent (EEUC) and north South Equatorial Current (nSEC). During the decaying phase, the reduction of the wind forcing and zonal sea surface height gradient produces a weakening of surface circulation. For the connected AMM–AZM, in addition to the intensified NECC, EEUC, and nSEC in spring, an anomalous north-equatorial wind curl excites an oceanic Rossby wave (RW) that is boundary-reflected into an equatorial Kelvin wave (KW). The KW reverses the thermocline slope, weakening the nSEC and EUC in boreal summer and autumn, respectively. During the developing spring phase of the AZM, the nSEC is considerably reduced with no consistent impact at subsurface levels. During the autumn decaying phase, the upwelling RW-reflected mechanism is activated, modifying the zonal pressure gradient that intensifies the nSEC. The NECC is reduced in boreal spring–summer. Our results reveal a robust alteration of the upper-ocean circulation during AMM, AZM, and AMM–AZM, highlighting the decisive role of ocean waves in connecting the tropical and equatorial ocean transport.
Paraules clau: Kelvin waves; Lagrangian circulation/transport; Ocean circulation; Rossby waves; Interannual variability; Tropical variability
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Orue-Echevarria D., Polzin K.L., Naveira Garabato A.C., Forryan A., Pelegrí J.L. (2023)
Journal of Geophysical Research: Oceans, 128 DOI: 10.1029/2022JC018730. (BibTeX: orue-echevarria.etal.2023)
Resum: Veure
The rates of isopycnal stirring and water mass transport by mesoscale eddies, and of diapycnal mixing by small-scale turbulence, across the Brazil-Malvinas Confluence (BMC) are assessed from a set of microstructure and hydrographic measurements in the Argentine Basin. This assessment is founded on a theoretical framework that applies a triple decomposition to the temperature variance equation and assumes eddies to transfer potential vorticity downgradient. The BMC is found to host widespread intense isopycnal stirring at rates of O(103–104 m2 s−1), and generally weak diapycnal mixing at rates of O(10−6–10−5 m2 s−1). Despite such disparity, both diapycnal mixing and isopycnal stirring play roles of comparable importance in determining regional water mass properties within surface and mode waters. In deeper layers, isopycnal stirring prevails. Eddies are further diagnosed to effect an important cross-BMC transport, at rates of O(1 m2 s−1). When scaled by the along-stream extent of the BMC, these rates integrate to volume transports that may be as large as O(10 Sverdrups). This suggests that cross-BMC transfers of waters are substantially effected by eddy-induced flows.
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Piracha A., Olmedo E., Turiel A., Portabella M., González-Haro C. (2023)
Frontiers in Marine Science, 10, 1020153 DOI: 10.3389/fmars.2023.1020153. (BibTeX: piracha.etal.2023)
Resum: Veure
For the first time, an accurate and complete picture of Mixed Layer (ML) water mass dynamics can be inferred at high spatio-temporal resolution via the material derivative derived from Sea Surface Salinity/Temperature (SSS/T) and Currents (SSC). The product between this satellite derived material derivative and in-situ derived Mixed Layer Depth (MLD) provides a satellite based kinematic approach to the water mass (trans)formation framework (WMT/F) above ML. We compare this approach to the standard thermodynamic approach based on air-sea fluxes provided by satellites, an ocean state estimate and in-situ observations. Southern Hemisphere surface density flux and water mass (trans)formation framework (WMT/F) were analysed in geographic and potential density space for the year 2014. Surface density flux differences between the satellite derived thermodynamic and kinematic approaches and ECCO (an ocean state estimate) underline: 1) air-sea heat fluxes dominate variability in the thermodynamic approach; and 2) fine scale structures from the satellite derived kinematic approach are most likely geophysical and not artefacts from noise in SSS/T or SSC—as suggested by a series of smoothing experiments. Additionally, ECCO revealed surface density flux integrated over ML are positively biased as compared to similar estimates assuming that surface conditions are homogeneous over ML—in part owing to the e-folding nature of shortwave solar radiation. Major differences between the satellite derived kinematic and thermodynamic approaches are associated to: 1) lateral mixing and mesoscale dynamics in the kinematic framework; 2) vertical excursions of, and vertical velocities through the ML base; and 3) interactions between ML horizontal velocities and ML base spatial gradients.
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Roget E., Pelegrí J.L., Planella-Morato J., Puigdefàbregas J., Emelianov M., Vallès-Casanova I., Orúe-Echevarria D. (2023)
Progress in Oceanography, 211, 102968 DOI: 10.1016/j.pocean.2023.102968. (BibTeX: roget.etal.2023)
Resum: Veure
Diapycnal mixing in the Brazil-Malvinas Confluence Zone (BMC) is assessed on the basis of microstructure measurements done as part of an April 2017 cruise, which explored the mesoscalar and regional frontal dynamics. Sampling was done down to 400 m in 11 locations on both sides of the BMC, over the slope and in the abyssal waters. Turbulent scales, non-dimensional numbers, energy dissipation rates and diapycnal eddy diffusivities are calculated, which allow us to assess the state of the small-scale turbulence in the frontal region. Active turbulence was present at all depths and stations, with high-dissipation patches ranging from several metres to a few tens of metres. The frontal zone is characterized by high energy dissipation and eddy diffusivity. The geometric mean eddy diffusivity for all stations and the entire water column is 7.0 × 10-4 m2 s−1. The mean values halve when only considering the more stratified seasonal thermocline, 3.8 × 10-4 m2 s−1, and are twice larger south than north of the BMC. High dissipation rates coincide with high vertical shear, possibly related to the convergence of the two intense currents and/or the generation of internal waves by the associated mesoscalar and submesoscalar features. The layered structures related to intruding filaments favor double diffusive convection and salt fingering. Near-bottom mixing at the stations on the continental slope is possible related to shear-driven Kelvin-Helmoltz instabilities.
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Xie J., Raj R.P., Bertino L., Martínez J., Gabarro C., Catany R. (2023)
Ocean Science, 19, 269-287. DOI: 10.5194/os-19-269-2023. (BibTeX: xie.etal.2023)
Resum: Veure
In the Arctic, the sea surface salinity (SSS) plays a key role in processes related to water mixing and sea ice. However, the lack of salinity observations causes large un- certainties in Arctic Ocean forecasts and reanalysis. Recently the Soil Moisture and Ocean Salinity (SMOS) satellite mis- sion was used by the Barcelona Expert Centre to develop an Arctic SSS product. In this study, we evaluate the impact of assimilating this data in a coupled ocean–ice data assimila- tion system. Using the deterministic ensemble Kalman filter from July to December 2016, two assimilation runs respec- tively assimilated two successive versions of the SMOS SSS product on top of a pre-existing reanalysis run. The runs were validated against independent in situ salinity profiles in the Arctic. The results show that the biases and the root-mean- squared differences (RMSD) of SSS are reduced by 10 % to 50 % depending on the area and highlight the importance of assimilating satellite salinity data. The time series of fresh- water content (FWC) further shows that its seasonal cycle can be adjusted by assimilation of the SSS products, which is encouraging of the assimilation of SSS in a long-time re- analysis to better reproduce the Arctic water cycle.
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Zoeller V., Viudez A. (2023)
Journal of Geophysical Research: Oceans, 128 DOI: 10.1029/2022JC019597. (BibTeX: zoeller.viudez.2023)
Resum: Veure
We investigate numerically the elastic interaction between an eddy-pair and an axisymmetrical eddy in inviscid isochoric two-dimensional (2D) flows, as well as in three-dimensional (3D) flows under the quasi-geostrophic (QG) approximation. The eddy-pair is a straight moving Lamb-Chaplygin dipole where the absolute value of either its positive or negative amount of vorticity equals the vorticity of the axisymmetrical eddy. The results for the 2D and 3D cases show that interactions with almost no vorticity exchange, or vorticity loss to the background field between ocean eddies, but causing changes in their displacement velocity, are possible. When the eddy-pair approaches the axisymmetrical eddy, their respective potential flows interact, the eddy-pair\'s trajectory acquires curvature and their vorticity poles separate. In the QG dynamics, the eddies suffer little vertical deformation, being the barotropic effects dominant. At the moment of highest interaction, the anticyclonic eddy of the pair elongates, simultaneously the cyclonic eddy of the pair evolves toward spherical geometry, and the axisymmetrical eddy acquires prolate ellipsoidal geometry in the vertically stretched QG space. Once the eddy-pair moves away from the axisymmetrical eddy, its poles close, returning to their original geometry, and the anticyclonic and cyclonic eddies continue as an eddy-pair with a straight trajectory but along a new direction. The interaction is sensitive to the initial conditions and, depending on the initial position of the eddy-pair, as well as on small changes in the vorticity distribution of the axisymmetrical eddy, inelastic interactions may instead occur
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Zoeller V., Viudez A. (2023)
Physics of Fluids, 35, 126607 DOI: 10.1063/5.0176659. (BibTeX: zoeller.viudez.2023a)
Resum: Veure
We provide exact solutions of axisymmetric neutral vortices, that is, vortices with zero amount of potential vorticity anomaly (PVA), in three- dimensional (3D) quasi-geostrophic (QG) flows with distributed vorticity and density stratification. These solutions are linear combinations of PVA spherical layer-modes, which consist of conveniently normalized spherical Bessel functions of order 0, truncated by a zero of the spherical Bessel function of order 1. It is shown that, depending on the superposition of the different spherical layer-modes, some vortices remain axisym- metrically robust to small amplitude PVA perturbations, while other vortices evolve to stable QG tripoles. The robust axisymmetric 3D QG vortices analyzed here do not generate exterior potential flow and may provide an explanation to the persistence of baroclinic eddies in the ocean.