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Research papers

The current filters are: Starting year = 2022, Ending year = 2023
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Biguino B., Olmedo E., Ferreira A., Zacarias N., Lamas L., Favareto L., Palma C., Borges C., Teles-Machado A., Dias J., Castellanos P., Brito A.C. (2022)
Remote Sensing, 14, 2, 423. DOI: 10.3390/rs14020423. (BibTeX: biguino.etal.2022)
Abstract: See
Salinity is one of the oldest parameters being measured in oceanography and one of the most important to study in the context of climate change. However, its quantification by satellite remote sensing has been a relatively recent achievement. Currently, after over ten years of data gathering, there are still many challenges in quantifying salinity from space, especially when it is intended for coastal environments study. That is mainly due to the spatial resolution of the available products. Recently, a new higher resolution (5 km) L4 SMOS sea surface salinity (SSS) product was developed by the Barcelona Expert Center (BEC). In this study, the quality of this product was tested along the Western Iberian Coast through its comparison with in situ observations and modelled salinity estimates (CMEMS IBI Ocean Reanalysis system). Moreover, several parameters such as the temperature and depth of in situ measurements were tested to identify the variables or processes that induced higher errors in the product or influenced its performance. Lastly, a seasonal and interannual analysis was conducted considering data between 2011 to 2019 to test the product as a potential tool for long-term studies. The results obtained in the present analysis showed a high potential of using the L4 BEC SSS SMOS product in extended temporal and spatial analyses along the Portuguese coast. A good correlation between the satellite and the in situ datasets was observed, and the satellite dataset showed lower errors in retrieving coastal salinities than the oceanic model. Overall, the distance to the coast and the closest rivers were the factors that most influenced the quality of the product. The present analysis showed that great progress has been made in deriving coastal salinity over the years and that the SMOS SSS product is a valuable contribution to worldwide climatological studies. In addition, these results reinforce the need to continue developing satellite remote sensing products as a global and cost-effective methodology for long-term studie
Keywords: surface salinity, SMOS, coastal ocean, CMEMS IBI Ocean reanalysis system, climate change
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Campuzano F., Santos F., Simionesei L., Oliveira A.R., Olmedo E., Turiel A., Fernandes R., Brito D., Alba M., Novellino A., Neves R. (2022)
Journal of Marine Science and Engineering, 10, 852 DOI: 10.3390/jmse10070852. (BibTeX: campuzano.etal.2022)
Abstract: See
The coupling of coastal or regional ocean models to hydrological models or observed data is currently an uncommon practice in operational oceanography. Though hydrological models are regarded as a powerful and useful tool for estimating the quantity and quality of freshwater running in a watershed, they fail to provide accurate results for river flow reaching the coastal area due to water-management activities occurring within the river catchment, activities such as human consumption, irrigation, storage, etc. For this reason, many coastal and regional ocean models continue to impose surface zero-salinity discharges as land boundary conditions for representing such a dynamic boundary. Moreover, river flows are based in climatologies, thus neglecting seasonal and interannual variability. To achieve those objectives, this study proposes an integrated methodology ranging from watershed models to validation in the coastal area and passing through methods and proxies for integrating the freshwater flows into regional ocean models. The main objective of this study is to explore the results obtained by using more sophisticated land boundary conditions based on the capacities of state-of-the-art hydrologic models combined with observation networks. In addition to the evaluation of the source of river-flow data, this work also explores the use of estuarine proxies based on simple modelling grids. The estuarine proxies enable the incorporation of the mixing processes that take place in estuaries into the land fluxes and obtain the plume momentum. The watershed, estuarine proxies, and ocean were modelled using the MOHID Water modelling system and evaluated in western Iberia waters. The modelling results served to illustrate the sea surface salinity extension of the Western Iberia Buoyant Plume (WIBP) during an extreme event in March 2018.
Keywords: freshwater discharges; operational oceanography; sea surface salinity; IBI region; land boundary; estuarine proxy; water continuum; numerical models
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Cazzaniga I., Zibordi G., Mélin F., Kwiatkowska E., Talone M., Dessailly D., Gossn J.I., Müller D. (2022)
IEEE Geoscience and Remote Sensing Letters, 19, 1-5. DOI: 10.1109/LGRS.2021.3136291. (BibTeX: cazzaniga.etal.2022)
Abstract: See
Radiometric water products from the Neural Network (NNv2) in the Alternative Atmospheric Correction (AAC) processing chain of Ocean and Land Colour Instruments (OLCI) were assessed over different marine regions. These products, not included among the operational ones, were custom produced from the Copernicus Sentinel-3 OLCI Baseline Collection 3. The assessment benefitted of in situ reference data from the Ocean Color component of the Aerosol Robotic Network (AERONET-OC) from sites representative of different water types. These included clear waters in the Western Mediterranean Sea, optically-complex waters characterized by varying concentrations of total suspended matter and chromophoric dissolved organic matter (CDOM) in the northern Adriatic Sea, and optically-complex waters characterized by very high concentrations of CDOM in the Baltic Sea. The comparison of the water-leaving radiances 𝑳𝑾𝑵 derived from OLCI data on board Sentinel-3A and Sentinel-3B with those from AERONETOC confirmed consistency between the products from the two satellite sensors. However, the accuracy of satellite data products exhibited dependence on the water type. A general underestimate of 𝑳𝑾𝑵 was observed for clear waters. Conversely, overestimates were observed for data products from optically-complex waters with the worst results obtained for CDOM-dominated waters. These findings suggest caution in exploiting NNv2 radiometric products, especially for highly absorbing and clear waters.
Keywords: Remote Sensing, Ocean Color, Validation
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Gabarró C., Fabregat P., Hernández-Maciá F., Jove R., Salvador J., Spreen G., Thielke L., Dadic R., Huntemann M., Kolabutin N., Nomura D., Hannula H.R., Schneebeli M. (2022)
Elementa: Science of the Anthropocene, 10, 1 DOI: 10.1525/elementa.2022.00031. (BibTeX: gabarro.etal.2022)
Abstract: See
Arctic sea ice is changing rapidly. Its retreat significantly impacts Arctic heat fluxes, ocean currents, and ecology, warranting the continuous monitoring and tracking of changes to sea ice extent and thickness. L-band (1.4 GHz) microwave radiometry can measure sea ice thickness for thin ice 1 m, depending on salinity and temperature. The sensitivity to thin ice makes L-band measurements complementary to radar altimetry which can measure the thickness of thick ice with reasonable accuracy. During the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition, we deployed the mobile ARIEL L-band radiometer on the sea ice floe next to research vessel Polarstern to study the sensitivity of the L-band to different sea ice parameters (e.g., snow and ice thickness, ice salinity, ice and snow temperature), with the aim to help improve/validate current microwave emission models. Our results show that ARIEL is sensitive to different types of surfaces (ice, leads, and melt ponds) and to ice thickness up to 70 cm when the salinity of the sea ice is low. The measurements can be reproduced with the Burke emission model when in situ snow and ice measurements for the autumn transects were used as model input. The correlation coefficient for modeled Burke brightness temperature (BT) versus ARIEL measurements was approximately 0.8. The discrepancy between the measurements and the model is about 5%, depending on the transects analyzed. No explicit dependence on snow depth was detected. We present a qualitative analysis for thin ice observations on leads. We have demonstrated that the ARIEL radiometer is an excellent field instrument for quantifying the sensitivity of L-band radiometry to ice and snow parameters, leading to insights that can enhance sea ice thickness retrievals from L-band radiometer satellites (such as Soil Moisture Ocean Salinity (SMOS) and Soil Moisture Active Passive (SMAP)) and improve estimates of Arctic sea-ice thickness changes on a larger scale
Keywords: Radiometry, Arctic, Emissivity, Sea ice, SMOS
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Gimeno J., Jorba À., Nicolás B., Olmedo E. (2022)
SIAM Journal on Applied Dynamical Systems, 21, 3, 1832-1861. DOI: 10.1137/21M1458363. (BibTeX: gimeno.etal.2022)
Abstract: See
In this paper we present a procedure to compute reducible invariant tori and their stable and unstable manifolds in Poincar´e maps. The method has two steps. In the first step we compute, by means of a quadratically convergent scheme, the Fourier series of the torus, its Floquet transformation,and its Floquet matrix. If the torus has stable and/or unstable directions, in the second step we compute the Taylor-Fourier expansions of the corresponding invariant manifolds up to a given order. The paper also discusses the case in which the torus is highly unstable so that a multiple shooting strategy is needed to compute the torus. If the order of the Taylor expansion of the manifolds is fixed and N is the number of Fourier modes, the whole computational effort (torus and manifolds) increases as OpN log Nq and the memory required behaves as OpNq. This makes the algorithm very suitable to compute high-dimensional tori for which a huge number of Fourier modes are needed. Besides, the algorithm has a very high degree of parallelism. The paper includes examples where we compute invariant tori (of dimensions up to 5) of quasi-periodically forced ODEs. The computations are run in a parallel computer and its efficiency with respect to the number of processors is also discussed.
Keywords: Parametrization method, Quasi-periodic Floquet Theory, Jet transport, and Parallel computing
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González-Gambau V., Olmedo E., Turiel A., González-Haro C., García-Espriu A., Martínez J., Alenius P., Tuomi L., Catany R., Arias M., Gabarró C., Hoareau N., Umbert M., Sabia R., Fernández D. (2022)
Earth System Science Data, 14, 2343-2368. DOI: 10.5194/essd-14-2343-2022. (BibTeX: gonzalezgambau.etal.2022)
Abstract: See
This paper presents the first Soil Moisture and Ocean Salinity (SMOS) Sea Surface Salinity (SSS) dedicated products over the Baltic Sea. The SSS retrieval from L-band brightness temperature (TB) measurements over this basin is really challenging due to important technical issues, such as the land–sea and ice–sea contamination, the high contamination by radio-frequency interference (RFI) sources, the low sensitivity of L-band TB at SSS changes in cold waters, and the poor characterization of dielectric constant models for the low SSS range in the basin. For these reasons, exploratory research in the algorithms used from the level 0 up to level 4 has been required to develop these dedicated products. This work has been performed in the framework of the European Space Agency regional initiative Baltic+ Salinity Dynamics. Two Baltic+ SSS products have been generated for the period 2011–2019 and are freely distributed: the Level 3 (L3) product (daily generated 9 d maps in a 0.25◦ grid; https://doi.org/10.20350/digitalCSIC/13859, González-Gambau et al., 2021a) and the Level 4 (L4) product (daily maps in a 0.05◦ grid; https://doi.org/10.20350/ digitalCSIC/13860, González-Gambau et al., 2021b), which are computed by applying multifractal fusion to L3 SSS with SST maps. The accuracy of L3 SSS products is typically around 0.7–0.8 psu. The L4 product has an improved spatiotemporal resolution with respect to the L3 and the accuracy is typically around 0.4 psu. Regions with the highest errors and limited coverage are located in Arkona and Bornholm basins and Gulfs of Finland and Riga. The impact assessment of Baltic+ SSS products has shown that they can help in the understanding of salinity dynamics in the basin. They complement the temporally and spatially very sparse in situ measurements, covering data gaps in the region, and they can also be useful for the validation of numerical models, particularly in areas where in situ data are very sparse.
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Grieco G., Stoffelen A., Verhoef A., Vogelzang J., Portabella M. (2022)
Remote Sensing, 14, 21, 5444. DOI: 10.3390/rs14215444. (BibTeX: grieco.etal.2022)
Abstract: See
The normalized standard deviation (Kp) of the noise that affects scatterometer Normalized Radar Cross-Sections (σ0s) plays a key role in the ocean and more in particular coastal wind retrieval procedures and the a posteriori quality control. This paper presents a method based on SeaWinds measurements to estimate Kps. The method computes the standard deviation of the differences between the full-resolution (slice) σ0s and the footprint (egg) σ0. The results are compared to the median of Kps provided with SeaWinds σ0s, showing some non-negligible differences. Kps estimated on non-homogeneous surfaces are larger than those estimated on sea, whereas no differences are appreciated in the provided Kps, which is likely due to the ability of this methodology to account for the effect of the scene variability in the estimates. The presence of inter-slice biases is demonstrated with a trend with the antenna azimuth angle. A multi-collocation slice cross-calibration procedure is suggested for the retrieval stage. Finally, a theoretical model of the distribution of σ0s is proposed and used to validate Kps. The results prove the efficacy of this model and that the provided Kps seem to be largely underestimated at low-wind regimes.
Keywords: SeaWinds; normalized radar cross-section noise; wind
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Isern-Fontanet J., Capet X., Turiel A., Olmedo E., González-Haro C. (2022)
Geophysical Research Letters, 49 DOI: 10.1029/2022GL098038. (BibTeX: isernfontanet.etal.2022)
Abstract: See
The contribution of ocean fronts to the properties and temporal evolution of Sea Surface Temperature (SST) structure functions have been investigated using a numerical model of the California Current system. First, the intensity of fronts have been quantified by using singularity exponents. Then, leaning on the multifractal theory of turbulence, we show that the departure of the scaling of the structure functions from a straight line, known as anomalous scaling, depends on the intensity of the strongest fronts. These fronts, at their turn, are closely related to the seasonal change of intensity of the coastal upwelling characteristics of this area. Our study points to the need to correctly reproduce the intensity of the strongest fronts and, consequently, properly model processes such as coastal upwelling in order to reproduce SST statistics in ocean models.
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King G.P., Portabella M., Lin W., Stoffelen A. (2022)
Remote Sensing, 14, 5, 1147. DOI: 10.3390/rs14051147. (BibTeX: king.etal.2022)
Abstract: See
Air–sea fluxes are greatly enhanced by the winds and vertical exchanges generated by mesoscale convective systems (MCSs). In contrast to global numerical weather prediction models, space-borne scatterometers are able to resolve the small-scale wind variability in and near MCSs at the ocean surface. Downbursts of heavy rain in MCSs produce strong gusts and large divergence and vorticity in surface winds. In this paper, 12.5 km wind fields from the ASCAT-A and ASCAT-B tandem mission, collocated with short time series of Meteosat Second Generation 3 km rain fields, are used to quantify correlations between wind divergence and rain in the Inter-Tropical Convergence Zone (ITCZ) of the Atlantic Ocean. We show that when there is extreme rain, there is extreme convergence/divergence in the vicinity. Probability distributions for wind divergence and rain rates were found to be heavy-tailed: exponential tails for wind divergence (P∼e −αδ with slopes that flatten with increasing rain rate), and power-law tails for rain rates (P∼(R ∗ ) −β with a slower and approximately equal decay for the extremes of convergence and divergence). Co-occurring points are tabulated in two-by-two contingency tables from which cross-correlations are calculated in terms of the odds and odds ratio for each time lag in the collocation. The odds ratio for extreme convergence and extreme divergence both have a well-defined peak. The divergence time lag is close to zero, while it is 30 min for the convergence peak, implying that extreme rain generally appears after (lags) extreme convergence. The temporal scale of moist convection is thus determined by the slower updraft process, as expected. A structural analysis was carried out that demonstrates consistency with the known structure of MCSs. This work demonstrates that (tandem) ASCAT winds are well suited for air–sea exchange studies in moist convection
Keywords: air–sea interaction; scatterometer winds; ASCAT; Meteosat Second Generation; ocean wind divergence; tropical convection; mesoscale convective systems; compound extremes; heavytailed PDFs
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Latasa M., Scharek R., Anxelu X., Morán G., Gutiérrez-Rodríguez A., Emelianov M., Salat J., Vidal M., Estrada M. (2022)
Progress in Oceanography, 201, 102737 DOI: 10.1016/j.pocean.2021.102737. (BibTeX: latasa.etal.2022)
Abstract: See
A detailed study of phytoplankton composition and dynamics was carried out during three contrasting situations (cruises F1, F2, and F3) in the northwestern (NW) Mediterranean Sea. Haptophytes, diatoms, and green algae dominated in F1, during the spring bloom, with high nutrients and high phytoplankton biomass. In F2, the postbloom situation with a still weak stratification and lower nutrient concentrations, we found a high spatial variability. Stations were clearly dominated by either Synechococcus, haptophytes or cryptophytes; with Syn echococcus reaching the highest abundance (4 × 105 cells mL− 1, 60% of the integrated chlorophyll a) reported to date for the open Mediterranean Sea. Cryptophytes accumulated close to the surface in very shallow mixed layer stations. In late summer, F3 revealed a fully developed stratification with low nutrients and a marked deep chlorophyll maximum (DCM). Prochlorococcus was present only during this cruise, mainly in deep layers together with haptophytes and pelagophytes, while haptophytes and Synechococcus dominated the upper mixed layer. Flow cytometry (FCM) and pigment-based abundance estimates for Prochlorococcus, Synechococcus and cryptophytes were well correlated, as happened also between small picoeukaryotes (FCM) and green algae (pigments), and between large picoeukaryotes (FCM) and haptophytes (pigments). Dinoflagellate abundance by microscopy and by pigments did not agree well, probably due to the presence of heterotrophic forms or because they contained pigments other than peridinin, the standard dinoflagellate marker. The decrease in size of the FCM large picoeukaryotes group with depth was presumably related to the increasing contribution of pelagophytes, with smaller cells than haptophytes, the other main component of this fraction. Cell size increase of Prochlorococcus and Synechococcus with depth suggests vertical segregation of genotypes or photoadaptation. The groups’ ecological preferences are presented with respect to depth and nutrient concentrations. Synechococcus and cryptophytes occupied shallow layers; diatoms, green algae and Prochlorococcus showed a tendency for deep layers and pelagophytes for even deeper layers, while haptophyte and dinoflagellate allocations were less clear. As for nutrients, the maximum relative contributions of green algae and especially diatoms occurred when dissolved inorganic phosphorus (DIP) concentrations were highest, of Prochlorococcus, dinoflagellates and pelagophytes when lowest, and of Synechococcus and cryptophytes when DIP concentrations were low but not minimal. The contribution of haptophytes did not show a relationship with DIP concentration. These results from individual groups stand as significant exceptions to the general relationship between phytoplankton cell size and nutrient availability.
Keywords: HPLC CHEMTAX Spring bloom Synechococcus bloom Ecological preferences Size distribution
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Lin W., Portabella M. (2022)
IEEE Transactions on Geoscience and Remote Sensing, 60, 1-10. DOI: 10.1109/TGRS.2022.3228317. (BibTeX: lin.portabella.2022)
Abstract: See
Recent advances in the sea surface wind quality control of the Advanced Scatterometer (ASCAT) show that spatial wind variability within a resolution cell of 25 km  25 km, namely the subcell wind variability, is highly correlated with the ASCAT quality indicators, such as the wind inversion residual (maximum likelihood estimator, MLE) and the singularity exponent (SE) derived from singularity analysis. This opens up opportunities for quantifying the instantaneous spatial wind variability over the global sea surface. In this paper, it is assumed that the spatial wind variability is linearly proportional to the temporal variation of buoy sea surface winds time-series following the Taylor’s hypothesis. As such, the moored buoy winds with 10-minute sampling are used to examine the subcell wind variability. Then the sensitivity of ASCAT quality indicators to the subcell wind variability is evaluated. The results indicate that although SE is more sensitive than MLE in characterizing the wind variability, they are mainly complementary in flagging the most variable winds. Consequently, an empirical model is derived to relate the buoy wind vector variability to the ASCAT MLE and/or SE values. Although the overall procedure is based on the one-dimensional temporal analysis and such empirical model cannot fully represent the two-dimensional spatial variability, it leads for the first time to the development of an ASCAT-derived local wind variability product. The empirical method presented here is straightforward and can be applied to other scatterometer systems.
Keywords: Advanced Scatterometer (ASCAT), wind variability, maximum likelihood estimator (MLE), singularity exponent (SE), subcell
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Liu S., Lin W., Portabella M., Wang Z. (2022)
Remote Sensing, 14, 4, 1035. DOI: 10.3390/rs14041035. (BibTeX: liu.etal.2022)
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The estimation of tropical cyclone (TC) intensity using Ku-band scatterometer data is challenging due to rain perturbation and signal saturation in the radar backscatter measurements. In this paper, an alternative approach to directly taking the maximum scatterometer-derived wind speed is proposed to assess the TC intensity. First, the TC center location is identified based on the unique characteristics of wind stress divergence/curl near the TC core. Then the radial extent of 17-m/s winds (i.e., R17) is calculated using the wind field data from the Haiyang-2B (HY-2B) scatterometer (HSCAT). The feasibility of HSCAT wind radii in determining TC intensity is evaluated using the maximum sustained wind speed (MSW) in the China Meteorological Administration best-track database. It shows that the HSCAT R17 value generally better correlates with the best-track MSW than the HSCAT maximum wind speed, therefore indicating the potential of using the HSCAT data to improve the TC nowcasting capabilities.
Keywords: scatterometer; tropical cyclone; wind radii; intensity; HY-2 satellite
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Lloret J., Turiel A., Solé J., Berdalet E., Sabatés A., Olivares A., Gili J.M., Vila-Subirós J., Sardá R. (2022)
Science of The Total Environment, 824, 153803 DOI: 10.1016/j.scitotenv.2022.153803. (BibTeX: lloret.etal.2022)
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The need for alternative energy systems like offshore wind power to move towards the Green Deal objectives is undeniable. However, it is also increasingly clear that biodiversity loss and climate change are interconnected issues that must be tackled in unison. In this paper we highlight that offshore wind farms (OWF) in the Mediterranean Sea (MS) pose serious environmental risks to the seabed and the biodiversity of many areas due to the particular ecological and socioeconomic characteristics and vulnerability of this semi-enclosed sea. The MS hosts a high diversity of species and habitats, many of which are threatened. Furthermore, valuable species, habitats, and seascapes for citizens\' health and well-being coexist with compounding effects of other economic activities (cruises, maritime transport, tourism activities, fisheries and aquaculture) in a busy space on a narrower continental shelf than in other European seas. We argue that simply importing the OWF models from the northern European seas, which are mostly based on large scale projects, to other seas like the Mediterranean is not straightforward. The risks of implementing these wind farms in the MS have not yet been well evaluated and, considering the Precautionary Principle incorporated into the Marine Strategy Framework Directive and the Maritime Spatial Planning Directive, they should not be ignored. We propose that OWF development in the MS should be excluded from high biodiversity areas containing sensitive and threatened species and habitats, particularly those situated inside or in the vicinity of Marine Protected Areas or areas with valuable seascapes. In the absence of a clearer and comprehensive EU planning of wind farms in the MS, the trade-off between the benefits (climate goals) and risks (environmental and socioeconomic impacts) of OWF could be unbalanced in favor of the risks
Keywords: Offshore energy Marine protected areas, environmental impacts, biodiversity Maritime spatial planning, seascape Renewable energy Mediterranean Sea
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Marín-Beltrán I., Demaria F., Ofelio C., Serra L.M., Turiel A., Ripple W.J., Mukul S.A., Costa M.C. (2022)
Science of The Total Environment, 811, 151359 DOI: 10.1016/j.scitotenv.2021.151359. (BibTeX: marinbeltran.etal.2022)
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The metabolism of contemporary industrialized societies, that is their energy and material flows, leads to the overconsumption and waste of natural resources, two factors often disregarded in the global ecological equation. In this Discussion article, we examine the amount of natural resources that is increasingly being consumed and wasted by humanity, and propose solutions to reverse this pattern. Since the beginning of the 20th century, societies, especially from industrialized countries, have been wasting resources in different ways. On one hand, the metabolism of industrial societies relies on non-renewable resources. On the other hand, yearly, we directly waste or mismanage around 78% of the total water withdrawn, 49% of the food produced, 31% of the energy produced, 85% of ores and 26% of non-metallic minerals extracted, respectively. As a consequence, natural resources are getting depleted and ecosystems polluted, leading to irreversible environmental changes, biological loss and social conflicts. To reduce the anthropogenic footprint in the planet, and live in harmony with other species and ourselves, we suggest to shift the current economic model based on infinite growth and reduce inequality between and within countries, following a degrowth strategy in industrialized countries. Public education to reduce superfluous consumption is also necessary. In addition, we propose a set of technological strategies to improve the management of natural resources towards circular economies that, like ecosystems, rely only upon renewable resources.
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Martínez J., Gabarró C., Turiel A., González-Gambau V., Umbert M., Hoareau N., González-Haro C., Olmedo E., Arias M., Catany R., Bertino L., Raj R.P., Xie J., Sabia R., Fernández D. (2022)
Earth System Science Data, 14, 1, 307–323. DOI: 10.5194/essd-14-307-2022. (BibTeX: martinez.etal.2022)
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Measuring salinity from space is challenging since the sensitivity of the brightness temperature (TB) to sea surface salinity (SSS) is low (about 0.5 K psu−1 ), while the SSS range in the open ocean is narrow (about 5 psu, if river discharge areas are not considered). This translates into a high accuracy requirement of the radiometer (about 2–3 K). Moreover, the sensitivity of the TB to SSS at cold waters is even lower (0.3 K psu−1 ), making the retrieval of the SSS in the cold waters even more challenging. Due to this limitation, the ESA launched a specific initiative in 2019, the Arctic+Salinity project (AO/1-9158/18/I-BG), to produce an enhanced Arctic SSS product with better quality and resolution than the available products. This paper presents the methodologies used to produce the new enhanced Arctic SMOS SSS product (Martínez et al., 2019) . The product consists of 9 d averaged maps in an EASE 2.0 grid of 25 km. The product is freely distributed from the Barcelona Expert Center (BEC, http://bec.icm.csic.es/, last access: 25 January 2022) with the DOI number https://doi.org/10.20350/digitalCSIC/12620 (Martínez et al., 2019). The major change in this new product is its improvement of the effective spatial resolution that permits better monitoring of the mesoscale structures (large than 50 km), which benefits the river discharge monitoring.
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Martínez J., García-Ladona E., Ballabrera-Poy J., Isern-Fontanet J., González-Motos S., Allegue J.M., González-Haro C. (2022)
Journal of Operational Oceanography DOI: 10.1080/1755876X.2022.2102357. (BibTeX: martinez.etal.2022b)
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Sea surface currents probably are the most relevant essential ocean variable affecting diverse societal challenges concerning the marine environmental (as, for example, safe and efficient navigation, marine pollution and ecological connectivity). This work introduces a climatological Atlas (monthly resolution) of currents in the Mediterranean and Canary–Iberian–Biscay basins, based on today’s state of the art reanalyses of the ocean circulation. The focus is on surface and subsurface reanalyses (here understood as z 0.5 and z 15 m, respectively) provided by the Copernicus Marine Environment Monitoring Service (CMEMS). The climatological values are computed from the median of the empirical probability density functions and the Atlas also includes the variance matrix and a bimodality index to have quantitative information on their variability. For both domains, the subsurface climatological fields are reasonably consistent with circulation schemes proposed in the previous literature but clearly improving the time and space resolution of the emerging patterns. For the Canary–Iberian–Biscay domain, the monthly climatological surface currents capture accurately the characteristic seasonal signal and its transition between a favourable and non-favourable upwelling regime. In the Mediterranean basin, differences between the near-surface and the 15 m velocity fields suggest a non- negligible role of winds over the variability of the uppermost ocean layer, specially in the Eastern Mediterranean basin. This is, up to our knowledge, the first time that such near-surface climatological patterns are computed. It has been found that, in general, the resulting patterns agree with surface drifter trajectories. In several regions, interannual variability foster bimodal and multimodal probability distributions. The Atlas has been conceived with the purpose of providing a first quantitative assessment on the surface circulation, thus being a complementary tool of real-time ocean forecasting systems. The Atlas is distributed following the FAIR principles and is accompanied with a digital version, with enhanced visualization capabilities for both research and assessment
Keywords: Currents, climatology, atlas, Mediterranean, Atlantic, Iberian; Canary, Biscay
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Miracca-Lage M., González-Haro C., Campagnoli-Napolitano D., Isern-Fontanet J., Simionatto-Polito P. (2022)
Journal of Geophysical Research: Oceans, 127 DOI: 10.1029/2021JC018001. (BibTeX: miraccalage.etal.2022)
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Satellite altimeters provide quasi-global measurements of sea surface height, and from those the vertically integrated geostrophic velocity can be directly estimated, but not its vertical structure. This study discusses whether the mesoscale (30–400 km) dynamics of three regions in the South Atlantic can be described by the surface quasi-geostrophic (SQG) theory, both at the surface and in depth, using outputs from an ocean general circulation model. At these scales, the model surface eddy kinetic energy (EKE) spectra show slopes close to k−5/3 (k−3) in winter (summer), characterizing the SQG and quasi-geostrophic (QG) turbulence regimes. We use surface density and temperature to (a) reconstruct the stream function under the SQG theory, (b) assess its capability of reproducing mesoscale motions, and (c) identify the main parameters that improve such reconstruction. For mixed layers shallower than 100 m, the changes in the mixed-layer depth contributes nine times more to the surface SQG reconstruction than the EKE, indicating the strong connection between the quality of the reconstruction and the seasonality of the mixed layer. To further explore the reconstruction vertical extension, we add the barotropic and first baroclinic QG modes to the surface solution. The SQG solutions reproduce the model density and geostrophic velocities in winter, whereas in summer, the interior QG modes prevail. Together, these solutions can improve surface correlations (>0.98) and can depict spatial patterns of mesoscale structures in both the horizontal and vertical domains. Improved spatial resolution from upcoming altimeter missions poses a motivating scenario to extend our findings into future observational studies.
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Nicolaus M., Perovich D.K., Spreen G., Granskog M.A., von Albedyll L., Angelopoulos M., Anhaus P., Arndt S., Belter H.J., Bessonov V., , Brauchle J., Calmer R., Cardellach E., Cheng B., , Dadic R., Damm E., de Boer G., Demir O., Dethloff K., Divine D.V., Fong A.A., Fons S., Frey M.M., Fuchs N., Gabarró C., , Goessling H.F., Gradinger R., Haapala J., Haas C., , Hannula H.R., Hen.dricks S, Herber A., Heuzé C., , Hoyland K.V., Huntemann M., Hutchings J.K., Hwang B., , Jacobi H.W., Jaggi M., Jutila A., Kaleschke L., Katlein C., , Krampe D., Kristensen S.S., Krumpen T., Kurtz N., , Lange B.A., Lei R., Light B., Linhardt F., Liston G.E., , Macfarlane A.R., Mahmud M., Matero I.O., Maus S., , Naderpour R., Nandan V., Niubom A., Oggier M., Oppelt N., Pätzold F., Perron C., Petrovsky T., Pirazzini R., Polashenski C., , Raphael I.A., Regnery J., Rex M., Ricker R., Riemann-Campe K., Rinke A., Rohde J., Salganik E., Scharien R.K., Schiller M., , Semmling M., Shimanchuk E., Shupe M.D., Smith M.M., , Sokolov V., Stanton T., Stroeve J., Thielke L., , Tonboe R.T., Tavri A., Tsamados M., Wagner D.N., , Webster M., Wendisch M. (2022)
Elementa: Science of the Anthropocene, 10, 1 DOI: 10.1525/ elementa.2021.000046. (BibTeX: nicolaus.etal.2022a)
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Year-round observations of the physical snow and ice properties and processes that govern the ice pack evolution and its interaction with the atmosphere and the ocean were conducted during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition of the research vessel Polarstern in the Arctic Ocean from October 2019 to September 2020. This work was embedded into the interdisciplinary design of the 5 MOSAiC teams, studying the atmosphere, the sea ice, the ocean, the ecosystem, and biogeochemical processes.The overall aim of the snow and sea ice observations during MOSAiC was to characterize the physical properties of the snow and ice cover comprehensively in the central Arctic over an entire annual cycle. This objective was achieved by detailed observations of physical properties and of energy and mass balance of snow and ice. By studying snow and sea ice dynamics over nested spatial scales from centimeters to tens of kilometers, the variability across scales can be considered. On-ice observations of in situ and remote sensing properties of the different surface types over all seasons will help to improve numerical process and climate models and to establish and validate novel satellite remote sensing methods; the linkages to accompanying airborne measurements, satellite observations, and results of numerical models are discussed. We found large spatial variabilities of snow metamorphism and thermal regimes impacting sea ice growth. We conclude that the highly variable snow cover needs to be considered in more detail (in observations, remote sensing, and models) to better understand snow-related feedback processes.The ice pack revealed rapid transformations and motions along the drift in all seasons. The number of coupled ice–ocean interface processes observed in detail are expected to guide upcoming research with respect to the changing Arctic sea ice
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Olivar M.P., Castellón A., Sabatés A., Sarmiento-Lezcano A., Emelianov M., Bernal A., Yang Y., Proud R., Brierley A.S. (2022)
Frontiers in Marine Science DOI: 10.3389/fmars.2022.1028717. (BibTeX: olivar.etal.2022)
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Mesopelagic fish populations are characterised by high species richness and abundance, and have been identified as important contributors to the active carbon fluxes in the open ocean. We report variability in communities of mesopelagic fish between five zones around the Iberian Peninsula, i.e. Balears and Alboran in the Mediterranean, and Cadiz, Lisboa and Galicia in the Atlantic. Day and night samples were collected from 7 layers of the water column with a midwater trawl fitted with a multisampler. Temperature and salinity regimes were very different on the Mediterranean and Atlantic sides of the peninsula, with much higher values through the entire water column in the Mediterranean, characterized by a strong pycnocline. The highest productivity was observed off Lisboa, where Chlorophyll a concentrations were two orders of magnitude higher than in any other zone. Samples from the western Mediterranean held 22 fish species, while 67 were found in the Atlantic. The lowest diversity and the highest dominance were observed in Balears, and the highest diversity in Cadiz zone. In all zones, but particularly in those in the Mediterranean, mesopelagic populations were dominated by a high number of small fish with low individual biomasses. The species Benthosema glaciale, Cyclothone pygmaea and Ceratoscopelus maderensis were common in the Mediterranean populations, whereas in the Atlantic, Cyclothone microdon/ livida, Valenciennellus tripunctulatus, Ceratoscopelus warmingii and Benthosema suborbitale were the most common species. Temperature and salinity (both at surface and in the mesopelagic zone) were the main environmental factors explaining variability in assemblage composition. A persistent (day-night) deep scattering layer was observed using the vessel based echosounder in all zones, and was comprised primarily of the gonostomatid Cyclothone spp. Night-time echosounder observations of scattering layers near the surface were observed in Balears, Alboran, Cadiz and Lisboa, where night surface net collections indicated that Myctophidae, Stomiidae and Phosichthyidae migration extended to the upper 100 m. Sternoptychids and the gonostomatid Sigmops elongatus seldom reached the upper 100 m in their night vertical migrations. Night stratified hauls of 30 m resolution carried out in the epipelagic zone showed that abundances maxima of migratory fish coincided with the location of the Chlorophyll a maxima.
Keywords: diversity, bristlemouths, lanternfishes, vertical migration, deep scattering layers
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Olmedo E., Turiel A., González-Gambau V., González-Haro C., García- Espriu A., Gabarró C., Portabella M., Corbella I., Martín-Neira M., Arias M., Catany R., Sabia R., Oliva R., Scipal K. (2022)
Scientific Reports, 12, 6279 DOI: 10.1038/s41598-022-10265-1. (BibTeX: olmedo.etal.2022)
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Changes in the Earth’s water cycle can be estimated by analyzing sea surface salinity. This variable reflects the balance between precipitation and evaporation over the ocean, since the upper layers of the ocean are the most sensitive to atmosphere–ocean interactions. In situ measurements lack spatial and temporal synopticity and are typically acquired at few meters below the surface. Satellite measurements, on the contrary, are synoptic, repetitive and acquired at the surface. Here we show that the satellite-derived sea surface salinity measurements evidence an intensification of the water cycle (the freshest waters become fresher and vice-versa) which is not observed at the in-situ near-surface salinity measurements. The largest positive differences between surface and near-surface salinity trends are located over regions characterized by a decrease in the mixed layer depth and the sea surface wind speed, and an increase in sea surface temperature, which is consistent with an increased stratification of the water column due to global warming. These results highlight the crucial importance of using satellites to unveil critical changes on ocean–atmosphere fluxes.
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Ortigosa I., Bardaji R., Carbonell A., Carrasco O., Castells-Sanabra M., Figuerola R., Hoareau N., Mateu J., Piera J., Puigdefabregas J., Salvador J., Simon C., Vallès-Casanova I., Pelegrí J.L. (2022)
Journal of Marine Science and Engineering, 10, 591 DOI: 10.3390/jmse100505. (BibTeX: ortigosa.etal.2022)
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Shelf waters near large cities, such as Barcelona, are affected not only by meteorological episodes but also by anthropogenic influence. Scientists usually use data from on-site coastal platforms to analyze and understand these complex water ecosystems because remote sensing satellites have low spatiotemporal resolution and do not provide reliable data so close to the coast. However, platforms with conventional oceanographic instrumentation are expensive to install and maintain. This study presents the scientific adaptation and initial measurements from a “patí a vela”, which is a very popular unipersonal catamaran in Barcelona. This versatile sailing vessel has been adapted to contain several low-cost sensors and instruments to measure water properties. Here, we describe the setup of a multi-parameter prototype, and then focus on results obtained using a low-cost temperature profiler. First, the temperature data are compared and validated with another conventional oceanographic instrument used in monthly oceanographic cruises. Then, field measurements between July and November 2021 are used to explore the relationship between air and water temperature in the Barcelona coastal area, showing the seasonal evolution of the temperature profile. We conclude that citizen sampling from fully sustainable sailing boats may turn into an effective strategy to monitor the urban coastal waters.
Keywords: scientific sailing boat; low-cost sensors; temperature-depth profiler; citizen science
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Ostrovskii A.G., Emelianov M.V., Kochetov O.Y., Kremenetskiy V.V., Shvoev D.A., Volkov S.V., Zatsepin A.G., Korovchinsky N.M., Olshanskiy V.M., Olchev A.V. (2022)
Journal of Marine Science and Engineering, 10, 322 DOI: 10.3390/jmse10030322. (BibTeX: ostrovskii.etal.2022)
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Biogeochemical cycles of carbon transformation throughout the euphotic zone of the sea are controlled by physical processes, e.g., daily thermocline, variation in solar irradiance, thermohaline convection, and intermittent mixing. These processes should be regularly observed with sufficient time resolution at fixed geographical locations. This study provides a brief overview of the carbon observational site in the Northeastern Black Sea. The focus is on the design of a new tethered profiler Winchi for the inner continental shelf part of the site. The profiler hull and two outriggers comprise an open trimaran platform that is positively buoyant and tends to maintain a horizontal position in the water. The lower end of the winch wire is secured to the bottom anchor. By unwinding/winding the wire, the profiler ascends/descends while measuring the depth profiles of marine environment parameters ranging from the seafloor to air–sea interface. After surfacing, the profiler determines its location using the Global Positioning System (GPS) and transmits data to (and from) a server on land through the Global System for Mobile Communications (GSM). Initial field tests with the Winchi profiler at the Northeastern Black Sea shelf exhibited promising results. We report these early tests to demonstrate the use of Winchi.
Keywords: greenhouse gases; carbon flux; tethered profiler; winch; real-time data transmission; Black Sea
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Polverari F., Portabella M., Lin W., Saap J.W., Stoffelen A., Jelenak Z., Chang P.S. (2022)
IEEE Transactions on Geoscience and Remote Sensing, 60 DOI: 10.1109/TGRS.2021.3079898. (BibTeX: polverari.etal.2022)
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Accurate high and extreme sea surface wind observations are essential for the meteorological, ocean, and climate applications. To properly assess and calibrate the current and future satellite-derived extreme winds, including those from the C-band scatterometers, building a consolidated high and extreme wind reference data set is crucial. In this work, a new approach is presented to assess the consistency between moored buoys and stepped-frequency microwave radiometer (SFMR)- derived winds. To overcome the absence of abundant direct collocations between these two data sets, the reprocessed Advanced Scatterometer (ASCAT)-A winds at the 12.5-km resolution, from 2009 to 2017, have been used to perform an indirect SFMR/buoy winds’ intercomparison. The ASCAT/SFMR analysis reveals an ASCAT wind underestimation for winds of above 15 m/s. SFMR measurements are calibrated using GPS drop-wind-sondes (dropsondes) data and averaged along-track to represent ASCAT spatially. On the other hand, ASCAT and buoy winds are in good agreement up to 25 m/s. The buoy high-wind quality has been confirmed using a triple collocation approach. Comparing these results, both SFMR and buoy winds appear to be highly correlated with ASCAT at the high-wind regime; however, they show a very different wind speed scaling. An SFMR-based recalibration of ASCAT winds is proposed, the so-called ASCAT dropsonde-scale winds, for use by the extreme wind operational community. However, further work is required to reconcile dropsonde (thus, SFMR) and buoy wind measurements under extreme wind conditions
Keywords: High and extreme wind speeds, microwave radiometry, ocean wind reference, spaceborne scatterometry
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Polverari F., Sapp J.W., Portabella M., Stoffelen A., Jelenak Z., Chang P.S. (2022)
IEEE Transactions on Geoscience and Remote Sensing, 60 DOI: 10.1109/TGRS.2022.3189310. (BibTeX: polverari.etal.2022a)
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The airborne Stepped Frequency Microwave Radiometer (SFMR) provides measurements of 10-m ocean- surface wind speed in high and extreme wind conditions. These winds are calibrated using the surface-adjusted wind estimates from the so-called dropsondes. The surface-adjusted winds are obtained from layer-averaged winds scaled to 10-m altitude to eliminate the local surface variability not associated with the storm strength. The SFMR measurements and, consequently, the surface-adjusted dropsonde winds represent a possible reference for satellite instrument and model calibration/validation at high and extreme wind conditions. To this end, representativeness errors that those measurements may introduce need to be taken into account to ensure that the storm variability is correctly resolved in satellite retrievals and modelling. In this work, we compare the SFMR winds with the dropsonde surface-adjusted winds derived from the so-called WL150 algorithm, which uses the lowest 150-meter layer between 10 m to 350 m. We use nine years of data from 2009 to 2017. We focus on the effects of the layer altitude and thickness. Our analysis shows that the layer altitude has a significant impact on dropsonde/SFMR wind comparisons. Moreover, the averaged winds obtained from layers thinner than the nominal 150 m and closer to the surface are more representative of the SFMR surface wind speed than the WL150 speeds. We also find that the surface-adjusted winds are more representative of 10-km horizontally averaged SFMR winds. We conclude that for calibration/validation purposes, the WL150 algorithm can introduce noise and the use of actual 10-m dropsonde measurements should be further investigated.
Keywords: Calibration, dropsondes, ocean surface high and extreme wind reference, tropical cyclones, microwave radiometry
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Portal G., Vall-llosera M., Piles M., Jagdhuber T., Camps A., Pablos M., López-Martínez C., Das N.N., Entekhabi D. (2022)
IEEE Transactions on Geoscience and Remote Sensing, 60, 1, 18. DOI: 10.1109/TGRS.2022.3187467. (BibTeX: portal.etal.2022)
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Incidence angle diversity of space-borne radiometer1 and radar systems operating at low microwave frequencies needs2 to be taken into consideration to accurately estimate soil mois-3 ture (SM) across spatial scales. In this study, the single channel4 algorithm (SCA) is first applied to Soil Moisture and Ocean5 Salinity (SMOS) brightness temperatures at vertical polarization6 (TBV ) to estimate SM at coarse resolution (25 km) and develop a7 land cover-specific and incidence angle (32.5◦ , 42.5◦, and 52.5◦ )-8 adaptive calibration of single scattering albedo (ω) and soil9 roughness (h s ) parameters. These effective parameters are used10 together with fine-scale multiangular Sentinel-1 backscatter in a11 single-pass active–passive downscaling approach to estimate TBV12 at fine scale (1 km) for each SMOS incidence angle. These TBV s13 are finally inverted to obtain the corresponding high-resolution14 SM maps. Results over the Iberian Peninsula for year 2018 show15 an increasing trend of ω and a decreasing trend of h s with16 SMOS incidence angle, with almost no variability of ω across17 land cover types. The active–passive covariation parameter is18 shown to increase with SMOS incidence angle and decrease with19 Sentinel-1 incidence angle. Coarse and fine TBV maps from the20 three SMOS incidence angles show similar distributions (mean differences below 0.38 K). Resulting high-resolution SM maps 22 have maximum differences in mean and standard deviation of 23 0.016 and 0.015 m3 /m3 , respectively, and compare well with 24 in situ measurements. Our results indicate that model-based 25 microwave approaches to estimate SM can be adequately adapted 26 to account for the incidence angle diversity of planned missions, 27 such as Copernicus Microwave Imaging Radiometer (CIMR), 28 Radar Observing System for Europe in L-band (ROSE-L), and 29 Sentinel-1 next generation.
Keywords: Active–passive microwave, incidence angle, radiometry, signal covariation, spatial disaggregation.
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Salvador X., Fernández-Vilert R., Moles J. (2022)
Journal of Natural history, 56, 5-8, 265-310. DOI: 10.1080/00222933.2022.2040630. (BibTeX: salvador.etal.2022)
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Citizen (or community) science has provided copious and valuable information about charismatic marine taxa such as heterobranch gastropods, thus contributing enormously to the known geographic distribution of many sea slug species. This study reports new records of elusive sea slugs in the coastal western Mediterranean (especially on the Catalan and French Mediterranean coasts) and contributes to new ecological information regarding their phenology, diet and behaviour. Out of 39 species reported here, 23 are new records for the Catalan coast (NE Spain), three are new records of pelagic pteropods for the Spanish Iberian coast, and eight are new records for the French Mediterranean coast. With 25 species found active at night, this study highlights the importance of sampling at night and in shallow, often under-sampled waters with high species diversity. Shallow waters usually have less diving activity and are harder to survey with heavy scuba equipment. We believe that the high-quality photos herein and the related species information will enable researchers, divers and the community to find and recognise these rare species in the Mediterranean basin.
Keywords: marine heterobranchs; new records; uncommon species; Mediterranean Sea; byodiversity
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Umbert M., Hoareau N., Salat J., Salvador J., Guimbard S., Olmedo E., Gabarró C. (2022)
Journal of Marine Science and Engineering, 10, 8 DOI: 10.3390/jmse10081078. (BibTeX: umbert.etal.2022b)
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The Vendée Globe is the world’s most famous solo, non-stop, unassisted sailing race. The Institute of Marine Sciences and the Barcelona Ocean Sailing Foundation installed a MicroCAT on the One Ocean One Planet boat. The skipper, Dídac Costa, completed the round trip in 97 days, from 8 November 2020 to 13 February 2021, providing one measurement of temperature and conductivity every 30 s during navigation. More than half of the ship’s route was in the sub-Antarctic zone, between the tropical and polar fronts, and it passed through areas of oceanographic interest such as Southern Patagonia (affected by glacier melting), the Brazil–Malvinas confluence, the Southern Pacific Ocean, and the entire Southern Indian Ocean. This sailing race gave a rare opportunity to measure in-situ sea surface salinity in a region where satellite salinity measurements are not reliable. Due to the decreased sensitivity of brightness temperature to salinity in cold seas, retrieving sea surface salinity at high latitudes remains a major challenge. This paper describes how the data are processed and uses the data to validate satellite salinity products in the sub-Antarctic zone. The sailing race measurements represent surface information (60 cm depth) not available from drifters or Argo floats. Acquiring measurements using round-the-world sailing races would allow us to analyse the evolution of ocean salinity and the impact of changes in the ice extent around Antarctica.
Keywords: sea surface temperature; sea surface salinity; ocean circumnavigation; ships of opportunity; SMOS validation; sub-Antarctic zone
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Vázquez A.J., Elosegui P., Lonsdale C.J., Crew G.B., Fish V.L., Ruszczyk C.A. (2022)
Publications of the Astronomical Society of the Pacific, 134, 1040, 12pp. DOI: https://doi.org/10.1088/1538-3873/ac8dc2. (BibTeX: vazquez.etal.2022)
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Correlation for radio interferometer array applications, including Very Long Baseline Interferometry (VLBI), is a multidisciplinary field that traditionally involves astronomy, geodesy, signal processing, and electronic design. In recent years, however, high-performance computing has been taking over electronic design, complicating this mix with the addition of network engineering, parallel programming, and resource scheduling, among others. High- performance applications go a step further by using specialized hardware like Graphics Processing Units (GPUs) or Field Programmable Gate Arrays (FPGAs), challenging engineers to build and maintain high-performance correlators that efficiently use the available resources. Existing literature has generally benchmarked correlators through narrow comparisons on specific scenarios, and the lack of a formal performance characterization prevents a systematic comparison. This combination of ongoing increasing complexity in software correlation together with the lack of performance models in the literature motivates the development of a performance model that allows us not only to characterize existing correlators and predict their performance in different scenarios but, more importantly, to provide an understanding of the trade-offs inherent to the decisions associated with their design. In this paper, we present a model that achieves both objectives. We validate this model against benchmarking results in the literature, and provide an example for its application for improving cost-effectiveness in the usage of cloud resources.
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Viudez A. (2022)
Journal of Fluid Mechanics, 949, A-13 DOI: 10.1017/jfm.2022.754. (BibTeX: viudez.2022a)
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Exact solutions of the time-dependent three-dimensional nonlinear vorticity equation for Euler flows with spherical geometry are provided. The velocity solution is the sum of a multipolar oscillatory function and a rigid cylindrical motion with swirl. The multipolar oscillation is a velocity mode whose radial and angular dependencies are given by the spherical Bessel functions and vector spherical harmonics, respectively. The local frequency of the velocity oscillations equals the angular speed of the rigid flow times the angular azimuthal wavenumber of the oscillating flow. The unsteady motion corresponds to inertial oscillations in multipolar flows with spatial azimuthal waves (non-vanishing azimuthal wavenumber) in the presence of a background flow with constant axial vorticity. In these nonlinear solutions, the curl of the Lamb vector has a linear dependence with the oscillation velocity, a property that makes it possible for the oscillating motion to satisfy different linear wave equations. Based on these inviscid time-dependent velocity modes, new exact solutions to the time-dependent Navier–Stokes equation are also provided.
Keywords: waves in rotating fluids, Navier–Stokes equations, vortex dynamics
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Viúdez A. (2022)
Journal of Fluid Mechanics, 936, A13 DOI: 10.1017/jfm.2022.73. (BibTeX: viudez.2022)
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Multipolar spherical solutions to the three-dimensional steady vorticity equation are provided. These solutions are based on the separation of radial and angular contributions in terms of the spherical Bessel functions and vector spherical harmonics, respectively. In this set of multipolar vortex solutions, the Hicks–Moffatt swirling vortex is categorized as a vortex of degree l = 1 and therefore as a vortex dipole. This swirling vortex is the three-dimensional dipole in spherical geometry equivalent to the two-dimensional Lamb–Chaplygin dipole in polar geometry. The three-dimensional dipole solution admits two linearly superposable solutions. The first one is a Trkalian flow and the second one is a cylindrical solid-body rotation with swirl. The higher l > 1 multipolar vortices found are either vanishing-helicity vortices or Trkalian flow vortices. The multipolar Trkalian flows admit two circular polarizations given by the sign of the wavenumber k. It is also found that piecewise vortex solutions, consisting of interior rotational and exterior potential flow domains, satisfying velocity continuity conditions at the vortex boundary, are possible in the general multipolar Trkalian spherical vortex. A particular polarized dipole solution in three-dimensional cylindrical geometry, consisting as well in the superposition of a Trkalian flow and a rigid motion, is also analysed. This swirling vortex may be interpreted as the three-dimensional dipole in cylindrical geometry equivalent to the two-dimensional Lamb–Chaplygin dipole in polar geometry.
Keywords: vortex flows
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Viúdez A. (2022)
European Journal of Mechanics B/Fluids, 98, 247-252. DOI: 10.1016/j.euromechflu.2022.12.011. (BibTeX: viudez.2022b)
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It is shown that a superposition of an arbitrary number of multipolar spherical and cylindrical oscillations in a cylindrical rigid flow with swirl is an exact solution to the time-dependent nonlinear vorticity equation. The oscillations are normal modes whose fundamental frequency and radial wavenumber are given by the angular speed and scaled inverse pitch, respectively, of the rigid flow.
Keywords: exact solucions, vortex flows, waves in swirling flow
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Wang S., Yang X., Portabella M., Yuen K.V., Zhang M., Du Y. (2022)
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 15, 8806-8818. DOI: 10.1109/JSTARS.2022.3213822. (BibTeX: wang.etal.2022)
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The tangential wind speed increases from the center to the eyewall of tropical cyclones (TC) along the radial direction and begins to decay when it extends outward. The tangential wind profile model is one of the most effective and widely used methods to reconstruct the TC radial wind speed. This article proposes a parametric tangential wind profile (TWP) model based on high- spatial-resolution synthetic aperture radar (SAR) imagery. The new model functions are piecewise with maximum tangential wind speed as a threshold, and all of them are designed as nonlinear. Notably, the derivative at the segmentation threshold is zero to ensure a smooth transition of the estimated wind speed profile. With the SAR-derived azimuth-averaged wind speed, we can determine the model parameters and get the tangential wind speed. The TWP model outperforms the commonly used single-modified Rankine vortex (SMRV) model, as it better resolves the tangential wind profile shape as depicted by both SAR-derived winds and hurricane hunter stepped-frequency microwave radiometer derived winds. A comprehensive analysis of the TWP model parameters is carried out by fitting tangential winds for 620 hurricane hunter flights. Interestingly, the tangential wind profiles for major hurricanes show a similar shape. The proposed TWP model can be used for improved TC characterization and forecasting purposes
Keywords: Parametric modeling, synthetic aperture radar (SAR), Tangential wind speed, tropical cyclone (TC)
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Woods S.M., Daskolia M., Joly A., Bonnet P., Soacha K., Liñán S., Woods T., Piera J., Ceccaroni L. (2022)
Sustainability, 14, 4078 DOI: 10.3390/su14074078. (BibTeX: woods.etal.2022)
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There is a growing acknowledgement that citizen observatories, and other forms of citizen- generated data, have a significant role in tracking progress towards the Sustainable Development Goals. This is evident in the increasing number of Sustainable Development Goals’ indicators for which such data are already being used and in the high-level recognition of the potential role that citizen science can play. In this article, we argue that networks of citizen observatories will help realise this potential. Drawing on the Cos4Cloud project as an example, we highlight how such networks can make citizen-generated data more interoperable and accessible (among other qualities), increasing their impact and usefulness. Furthermore, we highlight other, perhaps overlooked, advantages of citizen observatories and citizen-generated data: educating and informing citizen scientists about the Sustainable Development Goals and co-creating solutions to the global challenges they addres
Keywords: citizen science; citizen observatory; Sustainable Development Goals; interoperability; co-design; education
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Zhao X., Lin W., Portabella M., Wang Z., He Y. (2022)
Remote Sensing of Environment, 274, 113015 DOI: 10.1016/j.rse.2022.113015. (BibTeX: zhao.etal.2022)
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The Ku-band scatterometer onboard China France Oceanography Satellite (CFOSAT) observes the sea surface with two conically scanning fan beams. Compared to the prior Ku-band pencil beam scatterometers, this innovative observing mechanism provides more independent backscatter measurements at varying incidence and azimuth angles, as such it brings challenges for the sea surface wind inversion, particularly under rainy conditions. In this paper, the rain effects on the CFOSAT SCATterometer (CSCAT) are investigated using the collocated numerical weather prediction (NWP) wind data and the Global Precipitation Measurement (GPM) microwave imager (GMI) rain data. Similar to the prior Ku-band or C-band scatterometers, the sensitivity of CSCAT radar backscatter to rain substantially varies with wind speed, radar polarization and incidence angle. However, due to the complex observation geometries, rain effects on the CSCAT retrieved winds is more complex than that of prior scatterometers, which may lead to a remarkable underestimation of CSCAT wind speed at high winds and heavy rain conditions. A simple simulation method is used to clarify the relation between the retrieved wind speed and the dependency of radar rain effects on the incidence angle. It is found that the backscatter measurements at low incidence angles, which are generally underestimated at high winds and heavy rainy conditions, have a larger influence on the wind inversion minimization, leading to much lower retrieved wind speeds than those of ECMWF and the pencil beam scatterometer (e.g., Haiyang-2B scattometer). Under low and moderate rain conditions though, a more compensated effect between low and high incidence angle measurements is found, leading to generally unbiased CSCAT high winds, in contrast to the generally underestimated pencil-beam scatterometer winds.
Keywords: CFOSAT Scatterometer Backscatter Rain effects Wind quality
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Zibordi G., Talone M., Mélin F. (2022)
IEEE Geoscience and Remote Sensing Letters, 19, 1502905, 1-5. DOI: 10.1109/LGRS.2021.3134876. (BibTeX: zibordi.etal.2022)
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The quantification of uncertainties affecting satellite ocean color products is a fundamental step to ensure their compliance with mission and science requirements. This work investigated a methodology relying on the use of in situ radiometric data with known uncertainties to determine those affecting matching satellite data. By exploiting in situ radiometric data from the Ocean Color component of the Aerosol Robotic Network (AERONET-OC), an advanced method was applied to radiometric data products from the Ocean and Land Color Instruments onboard the Sentinel-3A satellite (OLCI-A) and the Visible Infrared Imager Radiometer Suite onboard the Suomi National-Polar Orbiting Partnership satellite (VIIRS-S). The results from the analysis support the relevance of the method proposed.
Keywords: Ocean color, remote sensing, uncertainties
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Zibordi G., Kwiatkowska E., Mélin F., Talone M., Cazzaniga I., Dessailly D., Gossn J.I. (2022)
Remote Sensing of Environment, 272, 112911. DOI: 10.1016/j.rse.2022.112911. (BibTeX: zibordi.etal.2022a)
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The Ocean and Land Color Instruments (OLCI) operated onboard the Copernicus Sentinel-3 satellites are providing globally distributed Ocean Color Radiometry (OCR) data products of relevance for environmental and climate applications. This work summarizes results on the assessment of fundamental OCR data from the Operational Baseline 3 Collection OL_L2M.003.01 of OLCI-A and OLCI-B onboard Sentinel-3A and Sentinel-3B, respectively. Evaluated products are the satellite derived normalized water-leaving radiance LWN(λ), aerosol optical depth at 865 nm τa(865) and Ångstrom ¨ exponent α determined in the near-infrared spectral region. The analyses were performed relying on in situ reference data from the Ocean Color component of the Aerosol Robotic Network (AERONET-OC) from sites representative of diverse water types. The comparison of OLCI-A and OLCI-B with AERONET-OC LWN(λ) for oligotrophic/mesotrophic waters shows cross-mission consistent spectral median percent differences (i.e., biases) varying within ±6% at the blue-green center-wavelengths. The analysis of data from regions characterized by optically complex waters, however, displays systematic negative biases for both OLCI-A and OLCI-B further increasing for waters dominated by chromophoric dissolved organic matter, thus suggesting a dependence of the atmospheric correction on water type. The direct inter-comparison of OLCI-B and OLCI-A LWN(λ) from the Tandem Phase characterized by Sentinel-3B and Sentinel-3A flying 30 s apart on the same orbit, shows spectral median percent differences lower than ±1% in the 412–560 nm interval, of approximately +5% at 620 and 665 nm, and − 7% at 400 nm. However, outside the Tandem Phase, the intercomparison of OLCI-B and OLCI-A data products indicates large and systematic differences explained by a notable dependence on the viewing angle. The evaluation of τa(865) and α across different geographic regions exhibits overestimated values between +48 and + 79% for the former and underestimated values between − 28% and − 41% for the latter. A complementary evaluation of OCR data products from the Visible Infrared Imager Radiometer Suite on board the Suomi National Polar-orbiting Partnership (VIIRS-S), proposed as a further indirect term of reference for OLCI-A and OLCI-B data, shows large underestimates of LWN(λ) with respect to the in situ reference data in the various water types at 410 nm. Nevertheless, opposite to OLCI-A and OLCI-B data products, absolute differences between VIIRS-S and in situ reference data do not reveal any large or systematic dependence on water type and satellite viewing angle. Overall results suggest the need for further developing the OLCI-A and OLCI-B atmospheric correction, possibly improving the capability to identify aerosol types and to model scattering processes.