Articles

Els filtres actuals son: Any inici = 2019, Any final = 2020
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Al-Nassar A.R., Pelegrí J.L., Sangrà P., Alarcon M., Jansa A. (2020)
International Journal of Climatology, 40, 2, 908-926. DOI: 10.1002/joc.6247. (BibTeX: alnassar.etal.2020)
Resum: Veure
We combine daily in situ precipitation data with meteorological reanalysis data inorder to explore the contribution of cut-off low systems to the seasonal and inter-annual rainfall variations over Baghdad from 2005 to 2016. During these 12 years(average rainfall of 131 ± 67 mm/year), 38 rainy cut-off lows brought 43% of thetotal precipitation, with extreme inter-annual variations. Indeed, precipitation asso-ciated with autumn cut-off lows was the principal factor that turned an arid into awet year: during the three most arid years cut-off lows contributed about 25% ofthe average rainfall (10 out of 40 mm/year) while during the three wettest yearsthey contributed near 67% (171 out of 254 mm/year). The extreme-rain cut-off lowsystems displayed analogous synoptic characteristics: upper-atmosphere diver-gence, upwards vertical motions in the middle atmosphere, and lower-atmospherewinds into central Iraq at times when the surface Red Sea and Persian Gulf waterswere warmer than the surface air. During those days previous to an extreme event,the surface waters cooled substantially and the amount of precipitable waterincreased largely, suggesting high latent heat transfer. In order to characterize thoseconditions that favour rainfall, we focus on the November 18–20, 2013 cut-off lowsystem, which led to the largest flooding and wettest year in Baghdad between2005 and 2016. The distribution of properties in the middle (500 hPa) and upper(250 hPa) troposphere shows that the region was affected by intense horizontaldivergence and upwards motions, coinciding with a surface low over the ArabianPeninsula that caused intense northwards winds over the Persian Gulf and broughtsubstantial moisture to central Iraq. The analysis of several stability indexes indi-cates that convective instability played a secondary role during the episode.
Paraules clau: cut-off low, extreme precipitation, Middle East, moisture source, rainfall records, synoptic conditions
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Ceccaroni L., Piera J., Wernand M.R., Zielinski O., Busch J.A., Jan Van Der Woerd H., Bardaji R., Friedrichs A., Novoa S., Thijsse P., Velickovski F., Blaas M., Dubsky K. (2020)
Plos One. Open acces, 15, 3, e023008. DOI: 10.1371/journal.pone.0230084. (BibTeX: ceccaroni.etal.2020a)
Resum: Veure
The European-Commission—funded project ‘Citclops’ (Citizens’ observatory for coast and ocean optical monitoring) developed methods, tools and sensors, which can be used by citizens to monitor natural waters, with a strong focus on long-term data series related to environmental sciences. The new sensors, based on optical technologies, respond to a number of scientific, technical and societal objectives, ranging from more precise monitoring of key environmental descriptors of the aquatic environment (water colour, transparency and fluorescence) to an improved management of data collected with citizen participation. The sensors were tested, calibrated, integrated on several platforms, scientifically validated and demonstrated in the field. The new methods and tools were tested in a citizen-science context. The general conclusion is that citizens are valuable contributors in quality and quantity to the objective of collecting, integrating and analysing fragmented and diverse environmental data. An integration of these data into data-analysis tools has a large potential to support authoritative monitoring and decision-making. In this paper, the project’s objectives, results, technical achievements and lessons learned are presented.
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Clavel-Henry M., Solé J., Kristiansen T., Bahamon N., Rotllant G., Company J.B. (2020)
Plos One. Open acces, 15, 1, e0223396. DOI: 10.1371/journal.pone.0223396. (BibTeX: clavelhenry.etal.2020a)
Resum: Veure
Information on the buoyancy of eggs and larvae from deep-sea species is rare but necessary for explaining the position of non-swimming larvae in thewater column.Due to embryonic morphology and ecology diversities,egg buoyancy has important variations within one species and among other ones.Nevertheless, it has hardly been explored if this buoyancy variability can be a strategy for deep-sea larvae to optimize their transport beyond their spawning areas.In the northwestern Mediterranean Sea, protozoea and mysis larvae of the commercial deep-sea shrimp Aristeus antennatus were recently foundin upper layers,but to present, earlier stages like eggs and nauplii have not been collected.Using a Lagrangian transport model and larva lcharacteristics, we evaluate the buoyancy and hydrodynamic effects on the transport of A.antennatus’ larvae in the northwestern Mediterranean Sea.The transport models suggested that 75% of buoyant eggs released between 500 and 800 m depth (i.e.,known spawning area),reached the upper water layers(0–75m depth).Then,according to the modeled larval drifts, three spawning regions were defined in the studied area: 1) the northern part,along a continental margin crossed by large submarine canyons; 2) the central part, with two circular circulation structures (i.e.,eddies); and 3) the southern part, with currents flowing through a channel.The number of larvae in the most upper layer (0–5m depth) was higher if the larval transport model accounted for the ascent of eggs and nauplii (81%) instead of eggs reaching the surface before hatching (50%).The larvae reaching the most water upper layer (0–5m depth) had higher rates of dispersal than the ones transported below the surface layer (deeper than 5 m depth).The results of larval dispersal simulations have implications for the understanding of A. antennatus larval ecology and for management decisions related to the shrimp fisheries in the northwestern Mediterranean Sea
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Clavel-Henry M., Bahamon N., Solé J., Gorelli G., García del Arco J.A., Carreton M., Rotllant G., Company J.B. (2020)
Journal of Marine Systems, 209, 103372 DOI: 10.1016/j.jmarsys.2020.103372. (BibTeX: clavelhenry.etal.2020b)
Resum: Veure
Submarine canyons aggregate numerous marine species and can affect the structure of benthic communities. However, analyses dedicated to assess the spatial distribution variability among several canyons are rare. In the northwestern Mediterranean Sea, three major submarine canyons consecutively indent the narrow margin. There, the abundance of deep-sea blue and red shrimp Aristeus antennatus (Crustacea: Decapoda), one of the most important fishery-targeted species in the western and central Mediterranean Sea, sustains relatively high incomes for the nearest fishing harbors. To date, the spatial distribution of this shrimp species has only been assessed on known fishing grounds, but it has neither been modeled simultaneously covering several submarine canyons nor according to the environmental conditions. In this study, we aimed to look over the spatiotemporal shrimp distribution in a region of the northwestern Mediterranean Sea with a particular interest in variations in the three submarine canyons. From summer landing data between 2005 and 2014, we implemented a species distribution model with georeferenced catches linked to environmental data of the shrimp habitats. The model showed that the bottom topography was one of the most essential variables to explain the spatial distribution of the catches and that the highest catch rates were between 475 m and 575 m depth. Overall, two canyons (Blanes and Palamós) sheltered high estimates of catches on the shallow and narrow part of their margins (at 510 and 565 m depth). Among them, 60% of estimated summer catches came from the Palamós Canyon, but this estimate shifted to the Blanes Canyon in summer 2008, probably due to variations in fishing fleet behavior. Modeled hypothetical temperature changes scenarios (to 1 °C warmer than the average) suggested the shrimp catches would decrease less in the Blanes Canyon (3% fewer catches than the average) than in the Palamós Canyon (20% fewer catches than the average). The information produced by the species distribution model allowed setting spawning locations and depths, which is useful to better understand the canyon influence on benthic communities and to parameterize larval transport models.
Paraules clau: Marine environment Species distribution model CPUE Fisheries, submarine canyons Mediterranean Sea
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Corbella I., Torres F., Closa J., Duffo N., Durán I., González-Gambau V., Martín-Neira M. (2020)
IEEE Geoscience and Remote Sensing Letters, 17, 3, 461-463. DOI: 10.1109/LGRS.2019.2923539. (BibTeX: corbella.etal.2020a)
Resum: Veure
A method for internally calibrating microwave total power radiometers by using only one level of noise injection is presented. It is based on having a previous accurate characterization of the receiver noise temperature, which used de facto as a second calibration standard. The method proves to be at least equivalent to the classical two level, as demonstrated through their intercomparison using the data provided by the Microwave Imaging Radiometer using Aperture Synthesis (MIRAS) on board the European Space Agency Soil Moisture and Ocean Salinity (SMOS) Satellite. The long-term stability in terms of retrieved brightness temperature using both methods has similar trends with a small advantage for the one-point approach proposed here.
Paraules clau: Calibration; Microwave radiometry
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Fraisl D., Campbell J., See L., Wehn U., Wardlaw J., Gold M., Moorthy I., Arias R., Piera J., Oliver J.L., Masó J., Penker M., Fritz S. (2020)
Sustainability Science, 15, 6, 1735-1751. DOI: 10.1007/s11625-020-00833-7. (BibTeX: fraisl.etal.2020d)
Resum: Veure
The UN Sustainable Development Goals (SDGs) are a vision for achieving a sustainable future. Reliable, timely, comprehensive, and consistent data are critical for measuring progress towards, and ultimately achieving, the SDGs. Data from citizen science represent one new source of data that could be used for SDG reporting and monitoring. However, information is still lacking regarding the current and potential contributions of citizen science to the SDG indicator framework. Through a systematic review of the metadata and work plans of the 244 SDG indicators, as well as the identifcation of past and ongoing citizen science initiatives that could directly or indirectly provide data for these indicators, this paper presents an overview of where citizen science is already contributing and could contribute data to the SDG indicator framework. The results demonstrate that citizen science is “already contributing” to the monitoring of 5 SDG indicators, and that citizen science “could contribute” to 76 indicators, which, together, equates to around 33%. Our analysis also shows that the greatest inputs from citizen science to the SDG framework relate to SDG 15 Life on Land, SDG 11 Sustainable Cities and Communities, SDG 3 Good Health and Wellbeing, and SDG 6 Clean Water and Sanitation. Realizing the full potential of citizen science requires demonstrating its value in the global data ecosystem, building partnerships around citizen science data to accelerate SDG progress, and leveraging investments to enhance its use and impact
Paraules clau: Sustainable Development Goals (SDGs); Citizen science; SDG indicators; Tier classifcation for SDG indicators; Crowdsourcing; Community-based monitoring
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García-Olivares A., Solé J., Samsó R., Ballabrera-Poy J. (2020)
Sustainability, 12, 12, 5091. DOI: 10.3390/su12125091. (BibTeX: garciaolivares.etal.2020a)
Resum: Veure
Europe must move towards a 100% renewable transportation system for climate, energyand sustainability reasons. We estimate the capital and energy required for building and operating arenewable transportation system providing similar services as the EU-28 transport system of 2016.It could be based on: biogas or fuel cell vessels; liquid biogas powered aircrafts; electric railways andfuel cell or electric vehicles between major cities; and car sharing, electric buses and electric two- andthree-wheelers, for short journeys. A system of charging posts on the streets and roads for passengerand commercial e-vehicles is studied. Alternatively, a Tracked Electric Vehicle system of continuouspower on European roads would improve energy efficiency and the saving of scarce metals (Ni, Li),at a lower cost, if only national roads were electrified. The investment for the construction of thewhole system would be 2.3–2.7% of the EU’s GDP per year for 30 years. The new system operationwould require 16% less energy than that of 2016, with reduction of 70% in road transport. However,shipping and aviation would demand 162% and 149% more energy, respectively, if liquefied biogaswere used as fuel. A type of land transport fully based on trains would provide a similar service tothat of an electric vehicle fleet, with a 29% lower energy consumption
Paraules clau: Transport infrastructure; Transition cost; Electrification; Embodied energy; Decarbonisation; Rail transport
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González-Gambau V., Turiel A., González-Haro C., Martínez J., Olmedo E., Oliva R., Martín-Neira M. (2020)
Remote Sensing, 12, 20, 3381. DOI: 10.3390/rs12203381. (BibTeX: gonzalezgambau.etal.2020a)
Resum: Veure
The error characterization of satellite observations is crucial for blending observations from multiple platforms into a unique dataset and for assimilating them into numerical weather prediction models. In the last years, the triple collocation (TC) technique has been widely used to assess the quality of many geophysical variables acquired with different instruments and at different scales. This paper presents a new formulation of the triple collocation (Correlated Triple Collocation (CTC)) for the case of three datasets that resolve similar spatial scales, with two of them being error-correlated datasets. Besides, the formulation is designed to ensure fast convergence of the error estimators. This approach is of special interest in cases such that finding more than three datasets with uncorrelated errors is not possible and the amount of data is limited. First, a synthetic experiment has been carried out to assess the performance of CTC formulation. As an example of application, the error characterization of three collocated L-band brightness temperature (TB) measurements over land has been performed. Two of the datasets come from ESA (European Space Agency) SMOS (Soil Moisture and Ocean Salinity) mission: one is the reconstructed TB from the operational L1B v620 product, and the other is the reconstructed TB from the operational L1B v620 product resulting from application of an RFI (Radio Frequency Interference) mitigation technique, the nodal sampling (NS). The third is an independent dataset, the TB acquired by a NASA (National Aeronautics and Space Administration) SMAP (Soil Moisture Active Passive) radiometer. Our analysis shows that the application of NS leads to TB error reduction with respect to the current version of SMOS TB in 80% of the points in the global map, with an average reduction of approximately 1 K over RFI-free regions and approximately 1.45 K over strongly RFI-contaminated areas.
Paraules clau: Triple collocation; Error characterization; Error cross-correlation; L-band brightness temperatures; SMOS (Soil Moisture and Ocean Salinity); SMAP (Soil Moisture Active Passive); NS (Nodal Sampling); RFI (Radio Frequency Interference) mitigation
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González-Haro C., Isern-Fontanet J., Tandeo P., Garello R. (2020)
Journal of Geophysical Research: Oceans, 125, 10, e2019JC015958. DOI: 10.1029/2019JC015958. (BibTeX: gonzalezharo.etal.2020a)
Resum: Veure
Abstract Knowledge of ocean surface current at high resolutions is crucial for many applications. In addition to the classic satellite altimetry retrieval from sea surface height (SSH), ocean surface currents can be retrieved from sea surface temperature (SST) observations using a transfer function between SST and SSH. Previous works showed the potential of microwave SST observations to reconstruct ocean surface currents using a synergistic approach: an optimal transfer function that combines the phase of SST with the SSH amplitude spectra. This synergistic approach revealed that surface quasi geostrophy (SQG) reconstruction can be enhanced and opened up the possibility to improve spatial resolution of ocean currents retrieved from altimeters observations if infrared SST observations are considered. However, before applying this synergistic approach to satellite observations, we need to analyze and characterize the spectral properties of the transfer function. This spectral characterization of the transfer function allows to exploit the synergy between SST and SSH observations that have different measurement topology and different spatial resolution. Here, we performed a feasibility study using the daily outputs of the operational Mercator global analysis and forecast system at (1/12)º in the western coast of Australia (27–35º S, 107–113º E) spanning from 26 November 2012 to 26 November 2016. Results showed that the mean transfer function in this region presents two well different bands: one characterized by a negative slope slightly steeper (a =−1.2) than the k −1 predicted by the SQG solution for scales smaller than 270 km and another characterized by a plateau for wavelengths larger than 270 km. In addition, the results revealed that the inhomogeneity in dynamics of the flow limits global solutions. Finally, we showed that information contained along the track is enough for a synoptic reconstruction of the flow in this region, which shows the feasibility of applying this methodology to real satellite observations.
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Grieco G., Stoffelen A., Portabella M. (2020)
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 13, 3-13. DOI: 10.1109/JSTARS.2019.2938327. (BibTeX: grieco.etal.2020)
Resum: Veure
Global navigation satellite system reflectometry (GNSS-R)-derived winds from the cyclone GNSS (CYGNSS) satellite constellation are expected to significantly improve weather forecasts in the tropical region. Delay–Doppler maps (DDMs) acquired by the TechDemosat-1 (TDS-1) GNSS-R satellite mission suffer from distortions that are highly correlated to on-board specular point estimation inaccuracies. Such distortions may affect wind retrievals, especially when multilook approaches aiming at exploiting the ambiguity-free area of the DDM are applied. This article demonstrates: that CYGNSS DDMs are also affected by such distortions; the rationale ofDDMshape asymmetries induced by specular point location inaccuracies; and a simple strategy for reducing such induced distortions.Two different datasets have been used, consisting of both regular and raw intermediate frequency CYGNSS measurements. The results show that, similar to TDS-1, the CYGNSS DDM distortions are correlated to specular point location inaccuracies. Furthermore, such inaccuracies are significantly reduced if more accurate specular point related parameters are used to recompress the raw GNSS-R echo, highlighting some sampling issues that are common to both TDS-1 and CYGNSS missions. These results suggest that multilook wind retrieval approaches aiming at exploiting also the peripheral parts of theDDM may be seriously compromised by such distortions. The latter may be substantially reduced by oversampling the outcomingDDMand by a posteriori choosing the proper DDM subsample. For future upcoming GNSS-R missions, it is strongly recommended to store the raw data for eventual reprocessing in case of miscalibration or processing issues such as those shown in this article.
Paraules clau: Delay–Doppler map (DDM) distortions; Dlobal navigation satellite system (GNSS); Reflectometry
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Herbert C., Pablos M., Vall-llossera M., Camps A., Martínez-Fernández J. (2020)
Remote Sensing, 12, 16, 2614. DOI: 10.3390/rs12162614. (BibTeX: herbert.etal.2020a)
Resum: Veure
A comprehensive understanding of temporal variability of subsurface soil moisture (SM) is paramount in hydrological and agricultural applications such as rainfed farming and irrigation. Since the SMOS (Soil Moisture and Ocean Salinity) mission was launched in 2009, globally available satellite SM retrievals have been used to investigate SM dynamics, based on the fact that useful information about subsurface SM is contained in their time series. SM along the depth profile is influenced by atmospheric forcing and local SM properties. Until now, subsurface SM was estimated by weighting preceding information of remotely sensed surface SM time series according to an optimized depth-specific characteristic time length. However, especially in regions with extreme SM conditions, the response time is supposed to be seasonally variable and depends on related processes occurring at different timescales. Aim of this study was to quantify the response time by means of the time lag between the trend series of satellite and in-situ SM observations using a Dynamic Time Warping (DTW) technique. DTW was applied to the SMOS satellite SM L4 product at 1 km resolution developed by the Barcelona Expert Center (BEC), and in-situ near-surface and root-zone SM of four representative stations at multiple depths, located in the Soil Moisture Measurements Station Network of the University of Salamanca (REMEDHUS) in Western Spain. DTW was customized to control the rate of accumulation and reduction of time lag during wetting and drying conditions and to consider the onset dates of pronounced precipitation events to increase sensitivity to prominent features of the input series. The temporal variability of climate factors in combination with crop growing seasons were used to indicate prevailing SM-related processes. Hereby, a comparison of long-term precipitation recordings and estimations of potential evapotranspiration (PET) allowed us to estimate SM seasons. The spatial heterogeneity of land use was analyzed by means of high-resolution images of Normalized Difference Vegetation Index (NDVI) from Sentinel-2 to provide information about the level of spatial representativeness of SMOS observations to each in-situ station. Results of the spatio-temporal analysis of the study were then evaluated to understand seasonally and spatially changing patterns in time lag. The time lag evolution describes a variable characteristic time length by considering the relevant processes which link SMOS and in-situ SM observation, which is an important step to accurately infer subsurface SM from satellite time series. At a further stage, the approach needs to be applied to different SM networks to understand the seasonal, climate- and site-specific characteristic behaviour of time lag and to decide, whether general conclusions can be drawn.
Paraules clau: Dynamic Time Warping; Soil moisture; SMOS; Time series analysis
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Isern-Fontanet J., García-Ladona E., Jiménez-Madrid J.A., Olmedo E., García-Sotillo M., Orfila A., Turiel A. (2020)
Remote Sensing, 12, 724-741. DOI: 10.3390/rs12040724. (BibTeX: isernfontanet.etal.2020a)
Resum: Veure
Surface currents in the Alboran Sea are characterized by a very fast evolution that is not well captured by altimetric maps due to sampling limitations. On the contrary, satellite infrared measurements provide high resolution synoptic images of the ocean at high temporal rate, allowing to capture the evolution of the flow. The capability of Surface Quasi-Geostrophic (SQG) dynamics to retrieve surface currents from thermal images was evaluated by comparing resulting velocities with in situ observations provided by surface drifters. A difficulty encountered comes from the lack of information about ocean salinity. We propose to exploit the strong relationship between salinity and temperature to identify water masses with distinctive salinity in satellite images and use this information to correct buoyancy. Once corrected, our results show that the SQG approach can retrieve ocean currents slightly better to that of near-real-time currents derived from altimetry in general, but much better in areas badly sampled by altimeters such as the area to the east of the Strait of Gibraltar. Although this area is far from the geostrophic equilibrium, the results show that the good sampling of infrared radiometers allows at least retrieving the direction of ocean currents in this area. The proposed approach can be used in other areas of the ocean for which water masses with distinctive salinity can be identified from satellite observations.
Paraules clau: sea surface temperature; altimetry; surface quasi-geostrophic equations; surface currents
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Martínez J., González-Gambau V., Gabarro C., Olmedo E. (2020)
Remote Sensing, 12, 15, 2425. DOI: 10.3390/RS12152425. (BibTeX: martinez.etal.2020a)
Resum: Veure
This book celebrates the ten year anniversary of the Barcelona Expert Center by presenting recent contributions related to the topics on which the team has been working during those years. The Barcelona Expert Center’s expertise covers a wide variety of remote sensing fields, but the main focus of the research is on the SMOS data processing and its ocean, land, and ice applications. This book contains 14 scientific papers addressing topics that go from the description of the new data processing algorithms that are implemented in the last version of the operational SMOS level 1 processor to scientific applications derived from SMOS: results on the sea-surface salinity assimilation in coastal models, synergies of the sea-surface salinity with temperature and chlorophyll and their impact on the better retrieval of ocean surface currents, quality assessment of SMOS-derived sea ice thickness, sea-surface salinity, and soil moisture products, among others. Moreover, one of the papers verifies the potential of the future Copernicus Imaging Microwave Radiometer (CIMR) mission within the CMEMS sea-surface salinity (SSS) operational production after the SMOS era.
Paraules clau: BEC; SMOS; Radiometry; Remote sensing; Oceanography; Soil moisture; Cryosphere; Processing; Sensor calibration; Image reconstruction
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Oliva R., Martín-Neira M., Corbella I., Closa J., Zurita A., Cabot F., Khazaal A., Kainulainen P., Barbosa J., Lopes G., Tenerelli J., Diéz-García R., González-Gambau V., Crapolicchio R. (2020)
Remote Sensing, 12, 10, 1645. DOI: 10.3390/rs12101645. (BibTeX: oliva.etal.2020a)
Resum: Veure
After more than 10 years in orbit, the SMOS team has started a new reprocessing campaign for the SMOS measurements, which includes the changes in calibration and image reconstruction that have been made to the Level 1 Operational Processor (L1OP) during the past few years. The current L1 processor, version v620, was used for the second mission reprocessing in 2014. The new version, v724, is the one run in the third mission reprocessing and will become the new operational processor. The present paper explains the major changes applied and analyses the quality of the data with different metrics. The results have been obtained with numerous individual tests that have confirmed the benefits of the evolutions and an end-to-end processing campaign involving three years of data used to assess the improvements of the SMOS measurements quantitatively.
Paraules clau: SMOS; Calibration; Radiometry; Reprocessing
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Olmedo E., González-Gambau V., Turiel A., Guimbard S., González-Haro C., Martínez J., Gabarró C., Portabella M., Arias M., Sabia R., Oliva R., Corbella I. (2020)
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 13, 6434-6453. DOI: 10.1109/JSTARS.2020.3034432. (BibTeX: olmedo.etal.2020)
Resum: Veure
The quality of the Soil Moisture and Ocean Salinity (SMOS) sea surface salinity (SSS) measurements has been noticeably improved in the past years. However, for some applications, there are still some limitations in the use of the Level-2 ocean salinity product. First, the SSS measurements are still affected by a latitudinal and seasonal bias. Second, the high standard deviation of the SSS error could significantly degrade part of the SSS signal. Finally, the coverage of the Level-2 salinity measurements is significantly reduced after applying filtering criteria to discard the poor-quality retrievals. In this work, we apply nodal sampling to the SMOS brightness temperatures (TBs), which effectively reduces the standard deviation of the TB error; then, we use debiased non-Bayesian retrieval for the mitigation of systematic biases on SSS and the statistical filtering criteria of the degraded salinity retrievals; and finally, we comprehensively characterize the residual latitudinal and seasonal biases and derive a correction for the retrieved SSS. We generate three years of an enhanced SMOS Level-2 Ocean Salinity product and we compare its performances with the ones corresponding to the European Space Agency SMOS Level-2 Ocean Salinity product (v662).
Paraules clau: Debiased non-Bayesian, latitudinal bias, near real-time sea surface salinity (SSS) product, nodal sampling, Soil Moisture and Ocean Salinity (SMOS), SSS.
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Orué-Echevarría D., Pelegrí J.L., Castellanos P., Guallar C., Marotta H., Marrasé C., Martín J., Masdeu-Navarro M., Paniagua G.F., Peña-Izquierdo J., Puigdefábregas J., Rodríguez.Fonseca B., Roget E., Rosell-Fieschi M., Salat J., Salvador J., Vallès-Casanova I., Vidal M., Viúdez A. (2020)
Data in Brief, 20, 105412. DOI: 10.1016/j.dib.2020.105412. (BibTeX: orueechevarria.etal.2020a)
Resum: Veure
This dataset, gathered during the RETRO-BMC cruise, reports multiple-scale measurements at the Confluence of the Brazil and Malvinas Currents. The cruise was carried out between 8 and 28 April 2017 onboard R/V Hespérides, departing from Ushuaia and arriving to Santos. Along its track, the vessel recorded near-surface temperature and salinity, as well as the horizontal flow from 20 m down to about 800 m. A total of 33 hydrographic stations were completed in a region off the Patagonian Shelf, within 41.2 °S–35.9 °S and out to 53.0 °W. At each station, a multiparametric probe and velocity sensors were deployed inside the frame of a rosette used to collect water samples at selected depths; these samples were later used for several water analyses, including inorganic nutri- ent concentrations. Microstructure measurements were car- ried out in 11 of these hydrographic stations. In addition, two high-resolution three-dimensional surveys were conducted with an instrumented undulating vehicle between 40.6 °S–39.0 °S and 55.6 °W–53.8 °W. Lastly, eight high-frequency ver- tical profilers were deployed in the region and five position- transmitting drifters were launched. These data allow the de- scription of the Confluence from the regional scale to the mi- croscale, and provide a view of the variability of the frontal region on time scales from days to weeks
Paraules clau: Brazil-Malvinas Confluence; Hydrographic data; SeaSoar data; Microstructure data
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Portal G., Jagdhuber T., Vall-llossera M., Camps A., Pablos M., Entekhabi D., Piles M. (2020)
Remote Sensing, 12(3), 570 DOI: 10.3390/rs12030570. (BibTeX: portal.etal.2020)
Resum: Veure
In the last decade, technological advances led to the launch of two satellite missions dedicated to measure the Earth’s surface soil moisture (SSM): the ESA’s Soil Moisture and Ocean Salinity (SMOS) launched in 2009, and the NASA’s Soil Moisture Active Passive (SMAP) launched in 2015. The two satellites have an L-band microwave radiometer on-board to measure the Earth’s surface emission. These measurements (brightness temperatures TB) are then used to generate global maps of SSM every three days with a spatial resolution of about 30–40 km and a target accuracy of 0.04 m3/m3. To meet local applications needs, different approaches have been proposed to spatially disaggregate SMOS and SMAP TB or their SSM products. They rely on synergies between multi-sensor observations and are built upon di erent physical assumptions. In this study, temporal and spatial characteristics of six operational SSM products derived from SMOS and SMAP are assessed in order to diagnose their distinct features, and the rationale behind them. The study is focused on the Iberian Peninsula and covers the period from April 2015 to December 2017. A temporal inter-comparison analysis is carried out using in situ SSM data from the Soil Moisture Measurements Station Network of the University of Salamanca (REMEDHUS) to evaluate the impact of the spatial scale of the dfferent products (1, 3, 9, 25, and 36 km), and their correspondence in terms of temporal dynamics. A spatial analysis is conducted for the whole Iberian Peninsula with emphasis on the added-value that the enhanced resolution products provide based on the microwave-optical (SMOS/ERA5/MODIS) or the active–passive microwave (SMAP/Sentinel-1) sensor fusion. Our results show overall agreement among time series of the products regardless their spatial scale when compared to in situ measurements. Still, higher spatial resolutions would be needed to capture local features such as small irrigated areas that are not dominant at the 1-km pixel scale. The degree to which spatial features are resolved by the enhanced resolution products depend on the multi-sensor synergies employed (at TB or soil moisture level), and on the nature of the fine-scale information used. The largest disparities between these products occur in forested areas, which may be related to the reduced sensitivity of high-resolution active microwave and optical data to soil properties under dense vegetation.
Paraules clau: soil moisture; moisture variability; temporal dynamics; moisture patterns; spatial disaggregation; Soil Moisture Active Passive (SMAP); Soil Moisture and Ocean Salinity (SMOS); REMEDHUS
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Raya V., Salat J., Sabatés A. (2020)
Marine Ecology Progress Series, 650, 289- 308. DOI: 10.3354/meps13369. (BibTeX: raya.etal.2020a)
Resum: Veure
This work develops a new method, the box-balance model (BBM), to assess the roleof hydrodynamic structures in the survival of fish larvae. The BBM was applied in the northwestMediterranean to field data, on 2 small pelagic fish species whose larvae coexist in summer:Engraulis encrasicolus,a dominant species, and Sardinella aurita, which is expanding northwardsin relation to sea warming. The BBM allows one to quantify the contribution of circulation, withsignificant mesoscale activity, to the survival of fish larvae, clearly separating the effect of trans-port from biological factors. It is based on comparing the larval abundances at age found in localtarget areas, associated with the mesoscale structures (boxes), to those predicted by the overallmortality rate of the population in the region. The application of the BBM reveals that dispersion/retention by hydrodynamic structures favours the survival ofE. encrasicoluslarvae. In addition,since larval growth and mortality rates of the species are required parameters for application of theBBM, we present their estimates forS. auritain the region for the first time. Although growth andmortality rates found forS. auritaare both higher than forE. encrasicolus, their combined effectconfers a lower survival to S. auritalarvae. Thus, although the warming trend in the region wouldcontribute to the expansion of the fast-growing species S. aurita, we can confirm that E. encrasi-colusis well established, with a better adapted survival strategy
Paraules clau: Engraulis encrasicolus; Sardinella aurita; Mortality; Growth; Fishlarvae; NW Mediterranean
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Reul N., Grodsky S.A., Arias M., Boutin J., Catany R., Chapron B., D\'Amico F., Dinnat E., Donlon C., Fore A., Fournier S., Guimbard S., Hasson A., Kolodziejczyk N., Lagerloef G., Lee T., Le Vine D.M., Lindstrom E., Maes C., Mecklenburg S., Meissner T., Olmedo E., Sabia R., Tenerelli J., Thouvenin-Masson C., Turiel A., Vergely J.L., Vinogradova N., Wentz F., Yueh S. (2020)
Remote Sensing of Environment, 242, 111769 DOI: 10.1016/j.rse.2020.111769. (BibTeX: reul.etal.2020a)
Resum: Veure
Operated since the end of 2009, the European Space Agency (ESA) Soil Moisture and Ocean Salinity (SMOS) satellite mission is the first orbiting radiometer that collects regular and global observations from space of two Essential Climate Variables of the Global Climate Observing System: Sea Surface Salinity (SSS) and Soil Moisture. The National Aeronautics and Space Administration (NASA) Aquarius mission, with the primary objective to provide global SSS measurements from space operated from mid-2011 to mid-2015. NASA\'s Soil Moisture Active- Passive (SMAP) mission, primarily dedicated to soil moisture measurements, but also monitoring SSS, has been operating since early 2015. The primary sensors onboard these three missions are passive microwave radiometers operating at 1.4 GHz (L-band). SSS is retrieved from radiometer measurements of the sea surface brightness temperature (TB). In this paper, we first provide a historical review of SSS remote sensing with passive L-band radiometry beginning with the discussions of measurement principles, technology, sensing characteristics and complementarities of the three aforementioned missions. The assessment of satellite SSS products is then presented in terms of individual mission characteristics, common algorithms, and measurement uncertainties, including the validation versus in situ data, and, the consideration of sampling differences between satellite SSS and in situ salinity measurements. We next review the major scientific achievements of the combined first 10 years of satellite SSS data, including the insights enabled by these measurements regarding the linkages of SSS with the global water cycle, climate variability, and ocean biochemistry. We also highlight the new ability provided by satellites to monitor mesoscale and synoptic-scale SSS features and to advance our understanding of SSS\' role in air-sea interactions, constraining ocean models, and improving seasonal predictions. An overview of satellite SSS observation highlights during this first decade and upcoming challenges are then presented.
Paraules clau: Sea surface salinity; Ocean microwave remote sensing; Radiometer; L-band; SMOS; Aquarius/SAC-D; SMAP
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Roca J.M., Pelegrí J.L. (2020)
, 160, 120185. DOI: 10.1016/j.ijheatmasstransfer.2020.120185. (BibTeX: roca.pelegri.2020a)
Resum: Veure
The large uncertainties in the forecasting of future global climatic conditions endorse the need of de- veloping simple yet credible predicting tools. Here we propose a three-zone steady-state radiative model that maximizes latitudinal heat fluxes and considers the potential effect of the Earth’s declination. The model is formulated as a set of five equations and six unknowns (zonal temperatures and widths, and the latitudinal heat transport) that requires specifying the reflected (albedo) and back-to-Earth (green- house) radiation fractions and obliges turning the low-latitude temperature into an additional parameter. The results do depend on the Earth declination, with changes of 0.5/1.5 K in the intermediate/high zones, which is interpreted as potentially affecting the greenhouse and high-latitude albedo coefficients. There- fore, we focus on identifying the effects of changes in these parameters –properly selected to represent last-glacial-maximum, modern and end-of the-century conditions. The main change is a large rise of the high-latitude temperature, favored both by a decrease in the high-latitude albedo and an increase in the greenhouse factor. For the other variables, the temporal changes in albedo and greenhouse gases com- pete among them, resulting in one trend from glacial to modern times and a reversal between preindus- trial times and the end of the 21st century (currently a warming-narrowing of the intermediate region and the widening of both the low- and high-latitude zones); however, we note that an increase in the low-latitude temperature would tend to alleviate these changes. Despite its simplicity, the model leads to realistic global trends, becoming a useful simple tool for exploring the sensitivity of the Earth’s heat distribution to changes in radiative fluxes and endorsing the validity of the maximum latitudinal-heat- transport premise.
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Rubino R., Duffo N., González-Gambau V., , Torres F., Durán I., Martín-Neira M. (2020)
Remote Sensing, 12, 10, 1604. DOI: 10.3390/rs12101604. (BibTeX: rubino.etal.2020a)
Resum: Veure
In this work, a new methodology is proposed in order to derive vertical total electron content (VTEC) maps from the radiometric measurements of the Soil Moisture and Ocean Salinity (SMOS) mission as an alternative approach to those based on external databases and models. This approach uses spatiotemporal filtering techniques with optimized filters to be robust against the thermal noise and image reconstruction artifacts present in SMOS images. It is also possible to retrieve the Faraday rotation angle from the recovered VTEC maps in order to correct the effect that it causes in the SMOS brightness temperatures.
Paraules clau: Faraday rotation angle (FRA); Vertical total electron content (VTEC); L-band; Radiometry; Interferometry; Soil moisture; Ocean salinity (SMOS)
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Sánchez-Gámez P., Gabarro C., Turiel A., Portabella M. (2020)
Remote Sensing, 12(4), 650 DOI: 10.3390/rs12040650. (BibTeX: sanchezgamez.etal.2020)
Resum: Veure
The European Space Agency (ESA) Soil Moisture and Ocean Salinity (SMOS) and the National Aeronautics and Space Administration (NASA) Soil Moisture Active Passive (SMAP) missions are providing brightness temperature measurements at 1.4 GHz (L-band) for about 10 and 4 years respectively. One of the new areas of geophysical exploitation of L-band radiometry is on thin (i.e., less than 1 m) Sea Ice Thickness (SIT), for which theoretical and empirical retrieval methods have been proposed. However, a comprehensive validation of SIT products has been hindered by the lack of suitable ground truth. The in-situ SIT datasets most commonly used for validation are affected by one important limitation: They are available mainly during late winter and spring months, when sea ice is fully developed and the thickness probability density function is wider than for autumn ice and less representative at the satellite spatial resolution. Using Upward Looking Sonar (ULS) data from theWoods Hole Oceanographic Institution (WHOI), acquired all year round, permits overcoming the mentioned limitation, thus improving the characterization of the L-band brightness temperature response to changes in thin SIT. State-of-the-art satellite SIT products and the Cumulative Freezing Degree Days (CFDD) model are verified against the ULS ground truth. The results show that the L-band SIT can be meaningfully retrieved up to 0.6 m, although the signal starts to saturate at 0.3 m. In contrast, despite the simplicity of the CFDD model, its predicted SIT values correlate very well with the ULS in-situ data during the sea ice growth season. The comparison between the CFDD SIT and the current L-band SIT products shows that both the sea ice concentration and the season are fundamental factors influencing the quality of the thickness retrieval from L-band satellites.
Paraules clau: L-band radiometry; Soil Moisture and Ocean Salinity (SMOS) mission; Soil Moisture Active Passive (SMAP); sea ice thickness; retrieval model validation; upward looking sonar; Arctic
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Sohn D.H., Park K.D., Davis J.L., Nettles M., Elosegui P. (2020)
Advances in Space Research, 65, 1673-1684. DOI: 10.1016/j.asr.2020.01.022. (BibTeX: sohn.etal.2020)
Resum: Veure
The Helheim glacier, located in southeast Greenland, has more than ten campaign-type Global Positioning System (GPS) sites; data processing led to the observation of a very rapid change in the ionospheric delay. To identify the cause of these sporadic disturbances, we analyzed the slant total electron content (STEC), single-differenced STEC (SD-STEC) and scintillation proxy index called the delta phase rate (DPR). From this analysis, the abrupt change of those ionospheric indicators was attributed to the line-of-sight direction to the satellite and the temporal sequence of the event was found to be highly correlated with the geometry of the GPS sites. In addition, the disturbance based on the result of SD-STEC occurred mostly during the night, from 17 UTC through 7 UTC, and across a band spanning the east-west direction. Based on the DPR indices obtained from GPS stations distributed across all of Greenland, Iceland, and northeastern Canada, the rapid ionospheric variation was found to be correlated with the time of the day and the geomagnetic latitude of the station. The disturbance was larger at the relatively low geomagnetic latitudes at night but was more significant at higher latitudes in the daytime. These rapid ionospheric variations tended to appear in band shapes parallel to the geomagnetic field. These results allow us to attribute such disturbance observed at the Helheim glacier to aurora-related phenomena.
Paraules clau: GPS; Rapid ionospheric variation; Slant total electron content (STEC); Delta phase rate (DPR); High latitude
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Solé J., Samsó R., García-Ladona E., García-Olivares A., Ballabrera-Poy J., Madurell T., Turiel A., Osychenko O., Álvarez D., Bardi U., Baumann M., Buchmann K., Capellán-Pérez I., Cerný M., Carpintero O., De Blas I., De Castro C., De Lathouwer J.-D., Duce C., Eggler L., Enríquez J.M., Falsini S., Feng K., Ferreras N., Frechoso F., Hubacek K., Jones A., Kaclíkova R., Kerschner C., Kimmich C., Lobejon L.F., L. Lomas P., Martelloni G., Mediavilla M., Miguel L.J., Natalini D., Nieto J., Nikolaev A., Parrado G., Papagianni S., Perissi I., Ploiner C., Radulov L., Rodrigo P., Sun L., Theofilidi M. (2020)
Renewable and Sustainable Energy Reviews, 132, 110105. DOI: 10.1016/j.rser.2020.110105. (BibTeX: sole.etal.2020a)
Resum: Veure
This paper reviews different approaches to modelling the energy transition towards a zero carbon economy. It identifies a number of limitations in current approaches such as a lack of consideration of out-of-equilibrium situations (like an energy transition) and non-linear feedbacks. To tackle those issues, the new open source integrated assessment model pymedeas is introduced, which allows the exploration of the design and planning of appropriate strategies and policies for decarbonizing the energy sector at World and EU level. The main novelty of the new open-source model is that it addresses the energy transition by considering biophysical limits, availability of raw materials, and climate change impacts. This paper showcases the model capabilities through several simulation experiments to explore alternative pathways for the renewable transition. In the selected scenarios of this work, future shortage of fossil fuels is found to be the most influential factor of the simulations system evolution. Changes in efficiency and climate change damages are also important determinants influencing model outcomes.
Paraules clau: Biophysical constraints; Climate damage; Energy efficiency; GHG emissions; Raw materials; Energy costs
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Sotomayor-Garcia A., Sala M.M., Ferrera I., Estrada M., Vázquez-Domínguez E., Emelianov M., Cortés P., Marrasé C., Ortega-Retuerta E., Nunes S., Castillo Y.M., Serrano Cuerva M., Sebastián M., Dall’Osto M., Simó R., Vaqué D. (2020)
Life, 10, 7, 107. DOI: 10.3390/life10070107. (BibTeX: sotomayorgarcia.etal.2020a)
Resum: Veure
We explored how changes of viral abundance and community composition among four contrasting regions in the Southern Ocean relied on physicochemical and microbiological traits. During January–February 2015, we visited areas north and south of the South Orkney Islands (NSO and SSO) characterized by low temperature and salinity and high inorganic nutrient concentration, north of South Georgia Island (NSG) and west of Anvers Island (WA), which have relatively higher temperatures and lower inorganic nutrient concentrations. Surface viral abundance (VA) was highest in NSG (21.50 ± 10.70 × 106 viruses mL−1) and lowest in SSO (2.96 ± 1.48 × 106 viruses mL−1). VA was positively correlated with temperature, prokaryote abundance and prokaryotic heterotrophic production, chlorophyll a, diatoms, haptophytes, fluorescent organic matter, and isoprene concentration, and was negatively correlated with inorganic nutrients (NO3−, SiO42−, PO43−), and dimethyl sulfide (DMS) concentrations. Viral communities determined by randomly amplified polymorphic DNA–polymerase chain reaction (RAPD-PCR) were grouped according to the sampling location, being more similar within them than among regions. The first two axes of a canonical correspondence analysis, including physicochemical (temperature, salinity, inorganic nutrients—NO3−, SiO42−, and dimethyl sulfoniopropionate -DMSP- and isoprene concentrations) and microbiological (chlorophyll a, haptophytes and diatom, and prokaryote abundance and prokaryotic heterotrophic production) factors accounted for 62.9% of the variance. The first axis, temperature-related, accounted for 33.8%; the second one, salinity-related, accounted for 29.1%. Thus, different environmental situations likely select different hosts for viruses, leading to distinct viral communities.
Paraules clau: Viral abundance; Viral community composition; Prokaryotes; Phytoplankton; Environmental variables; Secondary metabolic compounds; Southern Ocean; Antarctic Ocean; Antarctic Peninsula
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Stiles B.W., Portabella M., Yang X., Zheng G. (2020)
Remote Sensing, 12, 8, 3067. DOI: 10.3390/rs12183067. (BibTeX: stiles.etal.2020a)
Resum: Veure
Tropical cyclones (TCs) are essential for many reasons, including their destruction of humanlives and property and their effect on heat and nutrient fluxes between the ocean’s surface and itsdepths. A better understanding of ocean fluxes is needed to predict the impact of global climatechange on the oceans and to quantify how ocean heat content modulates the dynamics of globalclimate change. Similarly, improved modeling of nutrient fluxes is crucial for maintaining fisheriesand preserving crucial marine ecosystems to benefit both humanity and marine life. Numerousremote sensors measure crucial geophysical quantities before, during, and after TCs, including seasurface temperature (SST), ocean color, chlorophyll concentration, ocean surface winds, sea surfaceheight, and significant wave height. In this special issue, an international group of researchers havewritten articles describing (1) novel techniques and remote sensors for measuring the aforementionedquantities in tropical cyclones, (2) methods for validating and improving the accuracy of thosemeasurements and harmonizing them among different sensors, (3) scientific analyses that investigatethe relationships between remote-sensed ocean surface measurements and in situ measurementsof vertical profiles of ocean temperature, salinity, and current, and (4) strategies for utilizingremote-sensed measurements to improve operational forecasts in order to provide better tropicalcyclone warnings to human populations
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Tang W., Yueh S.H., Yang D., Mcleod E., Fore A., Hayashi A., Olmedo E., Martínez J., Gabarró C. (2020)
Remote Sensing, 12, 873 DOI: 10.3390/rs12050873. (BibTeX: tang.etal.2020)
Resum: Veure
Hudson Bay (HB) is the largest semi-inland sea in the Northern Hemisphere, connecting with the Arctic Ocean through the Foxe Basin and the northern Atlantic Ocean through the Hudson Strait. HB is covered by ice and snow in winter, which completely melts in summer. For about six months each year, satellite remote sensing of sea surface salinity (SSS) is possible over open water. SSS links freshwater contributions from river discharge, sea ice melt/freeze, and surface precipitation/evaporation. Given the strategic importance of HB, SSS has great potential in monitoring the HB freshwater cycle and studying its relationship with climate change. However, SSS retrieved in polar regions (poleward of 50º) fromcurrently operational space-based L-band microwave instruments has large uncertainty (~ 1 psu) mainly due to sensitivity degradation in cold water (<5ºC) and sea ice contamination. This study analyzes SSS from NASA Soil Moisture Active and Passive (SMAP) and European Space Agency (ESA) Soil Moisture and Ocean Salinity(SMOS) missions in the context of HB freshwater contents. We found that the main source of the year-to-year SSS variability is sea ice melting, in particular, the onset time and places of ice melt in the first couple of months of open water season. The freshwater contribution from surface forcing P-E is smaller in magnitude comparing with sea ice contribution but lasts on longer time scale through the whole open water season. River discharge is comparable with P-E in magnitude but peaks before ice melt. The spatial and temporal variations of freshwater contents largely exceed the remote sensed SSS uncertainty. This fact justifies the use of remote sensed SSS for monitoring the HB freshwater cycle.
Paraules clau: sea surface salinity; Hudson Bay; freshwater contents; sea ice; river discharge
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Trindade A., Portabella M., Stoffelen A., Lin W., Verhoef A. (2020)
IEEE Transactions on Geoscience and Remote Sensing, 58, 2, 1337-1347. DOI: 10.1109/TGRS.2019.2946019. (BibTeX: trindade.etal.2020a)
Resum: Veure
To address the growing demand for accurate high-resolution ocean wind forcing from the ocean modeling community, we develop a new forcing product, ERA*, by means of a geolocated scatterometer-based correction applied to the European Centre for Medium-range Weather Forecasts (ECMWF) reanalysis or ERA-interim (hereafter referred to as ERAi). This method successfully corrects for local wind vector biases present in the ERAi output globally. Several configurations of the ERA* are tested using complementary scatterometer data [advanced scatterometer (ASCAT)-A/B and oceansat-2 scatterometer (OSCAT)] accumulated over different temporal windows, verified against independent scatterometer data [HY-2A scatterometer (HSCAT)], and evaluated through spectral analysis to assess the geophysical consistency of the new stress equivalent wind fields (U10S). Due to the high quality of the scatterometer U10S, ERA* contains some of the physical processes missing or misrepresented in ERAi. Although the method is highly dependent on sampling, it shows potential, notably in the tropics. Short temporal windows are preferred, to avoid oversmoothing of the U10S fields. Thus, corrections based on increased scatterometer sampling (use of multiple scatterometers) are required to capture the detailed forcing errors. When verified against HSCAT, the ERA* configurations based on multiple scatterometers reduce the vector root-mean-square difference about 10% with respect to that of ERAi. ERA* also shows a significant increase in small-scale true wind variability, observed in the U10S spectral slopes. In particular, the ERA* spectral slopes consistently lay between those of HSCAT and ERAi, but closer to HSCAT, suggesting that ERA* effectively adds spatial scales of about 50 km, substantially smaller than those resolved by global numerical weather prediction (NWP) output over the open ocean (about 150 km).
Paraules clau: ERA*; Numerical weather prediction (NWP); Ocean wind forcing; Oceanic mesoscale; Scatterometer correction (SC); Scatterometer wind
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Umbert M., Guimbard S., Ballabrera J., Turiel A. (2020)
Remote Sensing, 12, 7, 1153. DOI: 10.3390/rs12071153. (BibTeX: umbert.etal.2020a)
Resum: Veure
The similarity of mesoscale and submesoscale features observed in different ocean scalars indicates that they undergo some common non-linear processes. As a result of quasi-2D turbulence, complicated patterns of filaments, meanders, and eddies are recognized in remote sensing images. A data fusion method used to improve the quality of one ocean variable using another variable as a template is used here as an extrapolation technique to improve the coverage of daily Aqua MODIS Level-3 chlorophyll maps by using MODIS SST maps as a template. The local correspondence of SST and Chl-a multifractal singularities is granted due to the existence of a common cascade process which makes it possible to use SST data to infer Chl-a concentration where data are lacking. The quality of the inference of Level-4 Chl-a maps is assessed by simulating artificial clouds and comparing reconstructed and original data.
Paraules clau: Remote sensing; Ocean color; Data fusion; Data merging; Physical oceanography; Singularity analysis
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Vallès‐Casanova I., Lee S.‐K., Foltz G.R., Pelegrí J.L. (2020)
Geophysical Research Letters, 47, 8, e2020GL087108. DOI: 10.1029/2020GL087108. (BibTeX: vallescasanova.etal.2020c)
Resum: Veure
The spatiotemporal evolutions of equatorial Atlantic sea surface temperature anomalies (SSTAs) during Atlantic Niño events and the associated climate impacts on the surrounding continents are extremely diverse. In this study, we construct longitude‐time maps of equatorial Atlantic SSTAs for each observed Atlantic Niño event during 1948–2019 and perform a spatiotemporal empirical orthogonal function analysis to identify the four most frequently recurring Atlantic Niño varieties. The first two contrast the timing of dissipation (early terminating vs. persistent) and the other two the timing of onset (early onset vs. late onset). Largely consistent with the differences in the timings of onset and dissipation, these four varieties display remarkable differences in rainfall response over West Africa and South America. Most of the varieties are subject to onset mechanisms that involve preconditioning in boreal spring by either the Atlantic meridional mode or Pacific El Niño, while for the late onset variability there is no clear source of external forcing.
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Viúdez A. (2020)
Journal of Fluid Mechanics, 890 DOI: 10.1017/jfm.2020.130. (BibTeX: viudez.2020a)
Resum: Veure
The permanent precession of a baroclinic geophysical vortex is reproduced, under he quasi-geostrophic approximation, using three potential vorticity anomaly modes in spherical geometry. The potential vorticity modes involve the spherical Bessel functions of the first kind jl(ρ)and the spherical harmonics Yml(θ, φ), where l is the degree, m is the order, and(ρ, θ, φ)are the spherical coordinates. The vortex precession is interpreted as the horizontal and circular advection by a large-amplitude background flow associated with the spherical modec0j0(ρ)of the small-amplitude zonal mode c2,0j2(ρ)Y02(θ) tilted by a small-amplitude mode c2,1j2(ρ)Y12(θ,φ), where {c0,c2,0,c2,1} are constant potential vorticity modal amplitudes. An approximate time-dependent, closed-form solution for the potential vorticity anomaly is given. In this solution the motion of the potential vorticity field is periodic but not rigid. The vortex precession frequencyω0depends linearly on the amplitudes c0 and c2,0 of the modal components of order 0, while the slope of the precessing axis depends on the ratio between the modal amplitude c2,1 and ω0.
Paraules clau: Baroclinic flows; Quasi-geostrophic flows
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Viúdez A. (2020)
Journal of Physical Oceanography, 50, 7, 2085-2087. DOI: 10.1175/JPO-D-19-0221.1. (BibTeX: viudez.2020c)
Resum: Veure
A 2019 comment by Hochet and Tailleux and the corresponding reply by Holmes et al. discuss the volume and mass balance on a control volume bounded by a given isotherm and the ocean free surface. This note partly reconciles the terms of discrepancy on volume or mass transport appearing in these publications by proving that the integral expressions in the comment of Hochet and Tailleux, using a particular parameterization of the moving surfaces in Cartesian coordinates, correspond to the mass transport across the moving surfaces, as long as the mass density is included, as given in direct vector notation by Holmes et al. in their reply.
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Arjona-Camas M., Puig P., Palanques A., Emelianov M., Durán R. (2019)
Journal of Marine Systems, 196, 86-96. DOI: 10.1016/j.jmarsys.2019.05.003. (BibTeX: arjonacamas.etal.2019a)
Resum: Veure
The temporal evolution of water column turbidity was studied on a submarine canyon on the Barcelona continental margin. From April to June 2014, an instrumented mooring array equipped with an autonomous hydrographic profiler with a CTD and a turbidimeter was deployed in the Foix canyon axis at 870 m depth. The instruments were programmed to collect hydrographic profiles once per day to provide a view of the temporal evolution of water column characteristics from 200 to 800 m water depth. The results illustrate a well-defined water turbidity structure of particulate matter distributed in intermediate nepheloid layers (INLs) developed between 300 and 500 m water depth and above the canyon rims, and INLs and near-bottom nepheloid layers (BNLs) confined inside the canyon between 650 and 800 m water depth. Data from fishing vessels activity at the time of the deployment was obtained from Vessel Monitoring System (VMS). The presence and location of the fishing vessels in the study area suggested a relationship between trawling activity and the generation of such layers. Nepheloid layers were absent during the first part of the deployment, when there was no fishing activity within the Foix Canyon axis or at the adjacent continental slope. Later, with the beginning of trawling activity on the fishing grounds close to the canyon, both INLs and BNLs were observed in the profiling casts, suggesting a causative relationship with fishing activities. Additionally, the hydrodynamic conditions within the canyon also seem to favour particle retention and to increase water turbidity in thick BNLs when water circulation is directed up-canyon. Bottom trawling appears to act as a main sediment resuspension mechanism in the Barcelona continental slope regions, increasing suspended sediment concentration at specific water depths where fishing grounds are located. Suspended particles are then advected and propagate along and across-margin by ambient currents via nepheloid layers.
Paraules clau: Submarine canyon; Sediment transport; Nepheloid structure; Bottom trawling; Resuspension; Northwestern Mediterranean
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Aulicino G., Cotroneo Y., Olmedo E., Cesarano C., Fusco G., Budillon G. (2019)
Remote Sensing, 11, 1361 DOI: 10.3390/rs11111361. (BibTeX: aulicino.etal.2019)
Resum: Veure
The Algerian Basin is a key area for the general circulation in the western Mediterranean Sea. The basin has an intense inflow/outflow regime with complex circulation patterns, involving both fresh Atlantic water and more saline Mediterranean water. Several studies have demonstrated the advantages of the combined use of autonomous underwater vehicles, such as gliders, with remotely sensed products (e.g., altimetry, MUR SST) to observe meso- and submesoscale structures and their properties. An important contribution could come from a new generation of enhanced satellite sea surface salinity (SSS) products, e.g., those provided by the Soil Moisture and Ocean Salinity (SMOS) mission. In this paper, we assess the advantages of using Barcelona Expert Center (BEC) SMOS SSS products, obtained through a combination of debiased non-Bayesian retrieval, DINEOF (data interpolating empirical orthogonal functions) and multifractal fusion with high resolution sea surface temperature (OSTIA SST) maps. Such an aim was reached by comparing SMOS Level-3 (L3) and Level-4 (L4) SSS products with in situ high resolution glider measurements collected in the framework of the Algerian Basin Circulation Unmanned Survey (ABACUS) observational program conducted in the Algerian Basin during falls 2014–2016. Results show that different levels of confidence between in situ and satellite measurements can be achieved according to the spatial scales of variability. Although SMOS values slightly underestimate in situ observations (mean dfference is -0.14 (-0.11)), with a standard deviation of 0.25 (0.26) for L3 (L4) products), at basin scale, the enhanced SMOS products well represent the salinity patterns described by the ABACUS data.
Paraules clau: sea surface salinity; BEC SMOS products; Mediterranean Sea; Algerian Basin; ABACUS gliders
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Bourassa M.A., Meissner T., Cerovecki I., Chang P.S., Dong X., De Chiara G., Donlon C., Dukhovskoy D.S., Elya J., Fore A., Fewings M.R., Foster R.C., Guille S.T., Haus B.K., Hristova-Veleva S., Holbach H.M., Jelenak Z., Knaff J.A., Kranz S.A., Manaster A., Mazloff M., Mears C., Mouche A., Portabella M., Reul N., Ricciardulli L., Rodríguez E., Sampson C., Solis D., Stoffelen A., Stukel M.R., Stiles B., Weissman D., Wentz F. (2019)
Frontiers in Marine Science, 6, 443 DOI: https://doi.org/10.3389/fmars.2019.00443. (BibTeX: bourassa.etal.2019)
Resum: Veure
Strengths and weakness of remotely sensed winds are discussed, along with the current capabilities for remotely sensing winds and stress. Future missions are briefly mentioned. The observational needs for a wide range of wind and stress applications are provided. These needs strongly support a short list of desired capabilities of future missions and constellations.
Paraules clau: satellite, wind, stress, ocean, requirements
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Cabré A., Pelegrí J.L., Vallès-Casanova I. (2019)
Journal of Geophysical Research: Oceans, 124, 7, 4820-4837. DOI: 10.1029/2019JC015160. (BibTeX: cabre.etal.2019)
Resum: Veure
Here we explore the water transfer between the subtropical and tropical gyres of the South Atlantic Ocean to better understand its unique equatorward heat delivery. A Lagrangian technique is applied to the reanalysis product GLORYS2V4 in order to trace back the western boundary flow in the tropical (North Brazil Undercurrent, NBUC) and subtropical (Brazil Current) gyres. Most of the northward NBUC core transport (14.9 Sv at 8°S) arrives from the eastern boundary subtropical current (Benguela Current) via the zonal South Equatorial Current. This subtropical‐tropical transfer represents the core of the returning limb of the Atlantic meridional overturning circulation and accounts for most of the observed increase in heat and salt‐volume transports (0.18 PW and 0.19 Sv from 30°S to 8°S, respectively) across the South Atlantic. The NBUC also includes Antarctic Intermediate Water below 400 m (7.4 Sv at 8°S) coming from the interior subtropical gyre, as well as water from the current\'s surface and peripheral components coming from the tropical gyre (13.3 Sv at 8°S). The Brazil Current (9.9 Sv at 29°S) is mostly composed of subtropical water originating in the upper 800mwest of the eastern boundary current at 30°S (8.5 Sv), with a minor contribution of surface tropical water that transfers to the subtropics (1.4 Sv).
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Carnicer O., De La Fuente P., Canepa A., Keith I., Rebolledo-Monsalve E., Diogène J., Fernández-Tejedor M. (2019)
, 6, 235 DOI: 10.3389/fmars.2019.00235. (BibTeX: carnicer.etal.2019)
Resum: Veure
It is likely that harmful algal blooms have increased in frequency, intensity, and geographic distribution in the last decades in response to anthropogenic activities. The Galápagos Islands are renowned for their exceptional biological diversity; however, marine dinoflagellate communities have not been represented in biodiversity assessments. Therefore, this study aims to provide key information about dinoflagellate diversity and abundances, with special attention to harmful species, during a weak La Niña event in the Galápagos Marine Reserve (GMR). The study was performed during March–April 2017 and four transects were conducted at four Islands (Santa Cruz, Santa Fé, Seymour, and Pinzón) representing the southern region of the GMR. Water net samples were collected at 2, 5, and 10 nautical miles (nm) from the coast, at a total of 48 sampling sites. The presence of toxic species, and their cell abundance was estimated in seven transects at 0, 15, and 30 m of depth. A total of 152 taxa belonging to 7 orders, 22 families, and 38 genera were registered. The number of taxa found is almost three times higher than the maximum observed in previous studies. Dinoflagellate species richness among stations ranged between 53 and 23 taxa and was higher in northern sites. From the applied cluster analysis, five dinoflagellate assemblages were identified as a discrete community structure, one was found only in Santa Fé Island, which is probably related to the presence of the Equatorial Undercurrent (EUC). Regarding cell abundance estimations, low abundances were registered throughout the sampling sites and no blooms were detected. Higher abundances were registered in the northern transects coinciding with one of the most productive areas of the archipelago, situated north of Santa Cruz. Among the identified taxa, 19 of them were potentially toxic, including epiphytic species, allowing the possibility of blooms in benthic areas. This study presents the first record of several dinoflagellate species in the area (both nontoxic and harmful species) and thus, emphasizing the need for the implementation of phytoplankton monitoring programs by the government to prevent potential ecological, sanitary and economic impacts in the GMR.
Paraules clau: harmful algal blooms, dinoflagellate assemblages, richness, spatial variability, CCA, Generalized Additive Models, environmental parameters
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Castellanos P., Olmedo E., Pelegrí J.L., Turiel A., Campos E.J.D. (2019)
Remote Sensing, 11, 7, 802. DOI: 10.3390/rs11070802. (BibTeX: castellanos.etal.2019a)
Resum: Veure
Three of the world’s most energetic regions are in the tropical and South Atlantic: the North Brazil Current Retroflection, the Brazil-Malvinas Confluence, and the Agulhas Current Retroflection. All three regions display offshore diversions of major boundary currents, which define the intensity of the returning limb of the Atlantic meridional overturning circulation. In this work, we use a sea-surface salinity (SSS) satellite product, combined with a high-resolution numerical model and in situ measurements, in order to explore the seasonal variation of the surface currents and transports in these three regions. The analysis of the model output shows that the SSS patterns reflect the surface velocity structure, with the largest horizontal SSS gradients coinciding with those areas of highest velocity and the most predominant velocity vector being 90º anticlockwise (clockwise) from the horizontal SSS gradient in the northern (southern) hemisphere. This information is then applied to the SSS satellite product to obtain maps of water velocity and salt transports, leading to a quantitative tool to estimate both water and salt transports in key regions of the world ocean.
Paraules clau: Sea surface salinity; SMOS; Retroflections; Surface velocity; Water transport; Salt transport
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Clavel-Henry M., Solé J., Ahumada-Sempoal M.A., Bahamon N., Briton F., Rotllant G., Company J.B. (2019)
Ocean Science, 15, 1745–1759. DOI: 10.5194/os-15-1745-2019. (BibTeX: clavelhenry.etal.2019)
Resum: Veure
Marine biophysical models can be used to explorethe displacement of individuals in and between submarinecanyons. Mostly, the studies focus on the shallow hydro-dynamics in or around a single canyon. In the northwest-ern Mediterranean Sea, knowledge of the deep-sea circula-tion and its spatial variability in three contiguous subma-rine canyons is limited. We used a Lagrangian frameworkwith three-dimensional velocity fields from two versions ofthe Regional Ocean Modeling System (ROMS) to study thedeep-bottom connectivity between submarine canyons andto compare their influence on the particle transport. From abiological point of view, the particles represented eggs andlarvae spawned by the deep-sea commercial shrimpAristeusantennatusalong the continental slope in summer. The pas-sive particles mainly followed a southwest drift along thecontinental slope and drifted less than 200 km consideringa pelagic larval duration (PLD) of 31 d. Two of the subma-rine canyons were connected by more than 27 % of parti-cles if they were released at sea bottom depths above 600 m.The vertical advection of particles depended on the depthwhere particles were released and the circulation influencedby the morphology of each submarine canyon. Therefore, theimpact of contiguous submarine canyons on particle trans-port should be studied on a case-by-case basis and not begeneralized. Because the flows were strongly influenced bythe bottom topography, the hydrodynamic model with finerbathymetric resolution data, a less smoothed bottom topogra-phy, and finer sigma-layer resolution near the bottom should give more accurate simulations of near-bottom passive drift.Those results propose that the physical model parameteriza-tion and discretization have to be considered for improvingconnectivity studies of deep-sea species
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Coll M., Pennino M.G., Steenbeek J., Sole J., Bellido J.M. (2019)
Ecological Modelling, 405, 86-101. DOI: 10.1016/j.ecolmodel.2019.05.005. (BibTeX: coll.etal.2019b)
Resum: Veure
The spatial prediction of species distributions from survey data is a significant component of spatial planning and the ecosystem-based management approach to marine resources. Statistical analysis of species occurrences and their relationships with associated environmental factors is used to predict how likely a species is to occur in unsampled locations as well as future conditions. However, it is known that environmental factors alone may not be sufficient to account for species distribution. Other ecological processes including species interactions (such as competition and predation), and the impact of human activities, may affect the spatial arrangement of a species. Novel techniques have been developed to take a more holistic approach to estimating species distributions, such as Bayesian Hierarchical Species Distribution model (B-HSD model) and mechanistic food-web models using the new Ecospace Habitat Foraging Capacity model (E-HFC model). Here we used both species distribution and spatial food-web models to predict the distribution of European hake (Merluccius merluccius), anglerfishes (Lophius piscatorius and L. budegassa) and red mullets (Mullus barbatus and M. surmuletus) in an exploited marine ecosystem of the Northwestern Mediterranean Sea. We explored the complementarity of both approaches, comparing results of food-web models previously informed with species distribution modelling results, aside from their applicability as independent techniques. The study shows that both modelling results are positively and significantly correlated with observational data. Predicted spatial patterns of biomasses show positive and significant correlations between modelling approaches and are more similar when using both methodologies in a complementary way: when using the E-HFC model previously informed with the environmental envelopes obtained from the B-HSD model outputs, or directly using niche calculations from B-HSD models to drive the niche priors of E-HFC. We discuss advantages, limitations and future developments of both modelling techniques.
Paraules clau: Spatial ecology Species distribution models Bayesian model Food-web model Ecospace Commercial species Mediterranean Sea
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Corbella I., Torres F., Duffo N., Duran I., González-Gambau V., Martín-Neira M. (2019)
Remote Sensing, 11, 682 DOI: 10.3390/rs11060682. (BibTeX: corbella.etal.2019a)
Resum: Veure
In microwave interferometric radiometers with a large field of view, as for example the Microwave Imaging Radiometer with Aperture Synthesis (MIRAS) onboard the Soil Moisture and Ocean Salinity (SMOS) satellite, one of the major causes of reconstruction error is the contribution to the visibility of the brightness temperature outside the fundamental period, defined on the basis of reciprocal grids. A mitigation method consisting of estimating this contribution through the application of a brightness temperature model outside the fundamental period is proposed. The main advantage is that it does not require any a posteriori addition of artificial scenes to the reconstructed image. Additionally, a method to avoid the sophisticated matrix regularization and inversion techniques usually applied in microwave interferometry is presented. Image reconstruction algorithms are implemented on a minimum grid size in order to maximize their numerical efficiency. An improved method to apply an apodization window to the reconstructed image for reducing Gibbs oscillations is also proposed. All procedures are generally described considering the single polarization case and successively implemented applying the MIRAS layout in both its single polarization and full polarimetric modes. Results show similar performance of the proposed algorithm with respect to the nominal one applied by SMOS. All algorithms are implemented in the MIRAS Testing Software and have been successfully used for scientific studies by other teams.
Paraules clau: interferometric radiometry; image reconstruction; error correction
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Corbella I., Torres F., Duffo N., Durán I., González-Gambau V., Oliva R., Closa J., Martín-Neira M. (2019)
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 12, 6, 1633-1646. DOI: 10.1109/JSTARS.2018.2885576. (BibTeX: corbella.etal.2019f)
Resum: Veure
The Microwave Imaging Radiometer with Aperture Synthesis (MIRAS) is formed by 69 total power radiometers, of which 3 are the noise-injection type. Their calibration is reviewed on the basis of the data gathered during more than eight years of operation. Internally calibrated gain and offset corrections with improved temporal stability are presented. New front-end loss characterization with lower seasonal dependence originated from external temperature swings is also proposed. Finally, a methodology to validate external calibrations, with the instrument pointing to the cold sky, is developed. It seems to indicate that the change of orientation of the instrument, with associated thermal variations, may induce small changes in the radiometer front-end losses, thus introducing calibration errors.
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Corcione V., Grieco G., Portabella M., Nunziata F., Migliaccio M. (2019)
IEEE Transactions on Geoscience and Remote Sensing, 57, 6, 3331-3340. DOI: 10.1109/TGRS.2018.2883364. (BibTeX: corcione.etal.2019a)
Resum: Veure
In this paper, the synthetic aperture radar (SAR) azimuth cutoff method is thoroughly revised and a new and general implementation is proposed. The key roles of the pixel spacing, the size of the image box, and the texture of the SAR scene are analyzed and optimized in terms of azimuth cutoff estimation. The reliability of the azimuth cutoff estimation is analyzed by measuring the distance between the measured and fitted autocorrelation functions. This analysis shows that it is of paramount importance to ilter unfeasible/unreliable azimuth cutoff values. To identify those values in an objective way, a criterion that is based on the \"Chi-squared\" test performed over a large data set of Sentinel-1 SAR imagery is defined and proven to be effective. The new robust implementation of the azimuth cutoff estimation at about 1-km grid spacing is then used to produce averaged azimuth cutoff at about 10-km grid spacing. The performance of the new estimation procedure, analyzed using a azimuth cutoff-to-wind-speed forward model, is shown to provide improved wind speed retrievals, with a root-mean-square error of 1.8–2 m/s when verified against independent numerical weather prediction model output and scatterometer winds.
Paraules clau: Cutoff frequency; Sea surface; Spectral analysis; Synthetic aperture radar
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Fournier S., Lee T., Tang W., Steele M., Olmedo E. (2019)
Remote Sensing, 11, 24, 3043. DOI: 10.3390/rs11243043. (BibTeX: fournier.etal.2019a)
Resum: Veure
Salinity is a critical parameter in the Arctic Ocean, having potential implications for climate and weather. This study presents the first systematic analysis of 6 commonly used sea surface salinity (SSS) products from the National Aeronautics and Space Administration (NASA) Aquarius and Soil Moisture Active Passive (SMAP) satellites and the European Space Agency (ESA) Soil Moisture and Ocean Salinity (SMOS) mission, in terms of their consistency among one another and with in-situ data. Overall, the satellite SSS products provide a similar characterization of the time mean SSS large-scale patterns and are relatively consistent in depicting the regions with strong SSS temporal variability. When averaged over the Arctic Ocean, the SSS show an excellent consistency in describing the seasonal and interannual variations. Comparison of satellite SSS with in-situ salinity measurements along ship transects suggest that satellite SSS captures salinity gradients away from regions with significant sea-ice concentration. The root-mean square differences (RMSD) of satellite SSS with respect to in-situ measurements improves with increasing temperature, reflecting the limitation of L-band radiometric sensitivity to SSS in cold water. However, the satellite SSS biases with respect to the in-situ measurements do not show a consistent dependence on temperature. The results have significant implications for the calibration and validation of satellite SSS as well as for the modeling community and the design of future satellite missions.
Paraules clau: Sea surface salinity; Arctic; SMAP; Aquarius; SMOS
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Gommenginger C., Chapron B., Hogg A., Buckingham C., Fox-Kemper B., Eriksson L., Soulat F., Ubelmann C., Ocampo-Torres F., Buongiorno-Nardelli B., Griffin D., Lopez-Dekker P., Knudsen P., Andersen O., Stenseng L., Stapleton N., Perrie W., Violante-Carvalho N., Schulz-Stellenfleth J., Woolf D., Isern-Fontanet J., Ardhuin F., Klein P., Mouche A., Pascual A., Capet X., Hauser D., Stoffelen A., Morrow R., Aouf L., Breivik O, Fu L.L., Johannessen J.A., Aksenov Y., Bricheno L., Hirschi J., Martin A.C.H., P. Martin A., Nurser G., Polton J., Wolf J., Johnsen H., Soloviev A., A. Jacobs G., Collard F., Groom S., Kudryavtsev V., Wilkin J., Navarro V., Babanin A., Martin M., Siddorn J., Saulter A., Rippeth T., Emery B., Maximenko N., Romeiser R., Graber H., Alvera-Azcarate A., W. Hughes C., Vandemark D., da Silva J., J. Van-Leeuwen P., Naveira-Garabato A., Gemmrich J., Mahadevan A., Marquez J., Munro Y., Doody S., Burbidge G. (2019)
Frontiers in Marine Science, 196, 86-96. DOI: 10.3389/fmars.2019.00457. (BibTeX: gommenginger.etal.2019a)
Resum: Veure
High-resolution satellite images of ocean color and sea surface temperature reveal an abundance of ocean fronts, vortices and filaments at scales below 10 km but measurements of ocean surface dynamics at these scales are rare. There is increasing recognition of the role played by small scale ocean processes in ocean-atmosphere coupling, upper-ocean mixing and ocean vertical transports, with advanced numerical models and in situ observations highlighting fundamental changes in dynamics when scales reach 1 km. Numerous scientific publications highlight the global impact of small oceanic scales on marine ecosystems, operational forecasts and long-term climate projections through strong ageostrophic circulations, large vertical ocean velocities and mixed layer re-stratification. Small-scale processes particularly dominate in coastal, shelf and polar seas where they mediate important exchanges between land, ocean, atmosphere and the cryosphere, e.g., freshwater, pollutants. As numerical models continue to evolve toward finer spatial resolution and increasingly complex coupled atmosphere-wave-ice-ocean systems, modern observing capability lags behind, unable to deliver the high-resolution synoptic measurements of total currents, wind vectors and waves needed to advance understanding, develop better parameterizations and improve model validations, forecasts and projections. SEASTAR is a satellite mission concept that proposes to directly address this critical observational gap with synoptic two-dimensional imaging of total ocean surface current vectors and wind vectors at 1 km resolution and coincident directional wave spectra. Based on major recent advances in squinted along-track Synthetic Aperture Radar interferometry, SEASTAR is an innovative, mature concept with unique demonstrated capabilities, seeking to proceed toward spaceborne implementation within Europe and beyond.
Paraules clau: Satellite; Air sea interactions; Upper ocean dynamics; Submesoscale; Coastal; Marginal ice zone; Radar; Along-track interferometry
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González-Haro C., Ponte A., Autret E. (2019)
Remote Sensing, 11, 19, 2313. DOI: 10.3390/rs11192313. (BibTeX: gonzalezharo.etal.2019)
Resum: Veure
The expected amplitude of fixed-point sea surface temperature (SST) fluctuations induced by barotropic and baroclinic tidal flows is estimated from tidal current atlases and SST observations. The fluctuations considered are the result of the advection of pre-existing SST fronts by tidal currents. They are thus confined to front locations and exhibit fine-scale spatial structures. The amplitude of these tidally induced SST fluctuations is proportional to the scalar product of SST frontal gradients and tidal currents. Regional and global estimations of these expected amplitudes are presented. We predict barotropic tidal motions produce SST fluctuations that may reach amplitudes of 0.3 K. Baroclinic (internal) tides produce SST fluctuations that may reach values that are weaker than 0.1 K. The amplitudes and the detectability of tidally induced fluctuations of SST are discussed in the light of expected SST fluctuations due to other geophysical processes and instrumental (pixel) noise. We conclude that actual observations of tidally induced SST fluctuations are a challenge with present-day observing systems.
Paraules clau: sea surface temperature; satellite observations; tidal currents; internal tides
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Grieco G., Stoffelen A., Portabella M., Belmonte M., Lin W., Fabra F. (2019)
IEEE Transactions on Geoscience and Remote Sensing, 57, 5, 2990-3000. DOI: 10.1109/TGRS.2018.2879059. (BibTeX: grieco.etal.2019c)
Resum: Veure
A quality control scheme for TechDemoSat 1 (TDS-1) and Cyclone Global Navigation Satellite System (GNSS) delay-Doppler maps (DDMs) is presented and the results of its application to a data set of more than 700 000 DDMs are discussed. This scheme is proven to be effective for such purpose and its output indices can be successfully used as quality indicators of the DDM. This paper shows that most of the TDS-1 DDMs are affected by some distortions that are attributable to an insufficiently accurate estimation of the specular point location. The errors, moreover, can severely alter the symmetry of the isodelay lines with respect to the iso-Doppler lines leading to an asymmetry in the arrival time of the waveforms. Furthermore, these errors may affect the convolution of the GNSS reflected signal with the Woodward ambiguity function, leading to an unwanted redistribution of the incoming echo energy among the DDM bins. Such distortions may, in turn, affect the accuracy of the wind field retrieval using either the stare processing approach or the more consolidated methods of inverting a Geophysical Model Function based on the DDM peak and/or leading edge slope.
Paraules clau: Accuracy; Error; Quality Control (QC); Reflected Global Navigation Satellite System (GNSS-R); Stare processing; Wind
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Guallar C., Flos J. (2019)
Progress in Oceanography, 176 (BibTeX: guallar.flos.2019)
Resum: Veure
The link between phytoplankton primary production (PPP) and chromophoric dissolved organic matter (CDOM) has been demonstrated indirectly in the laboratory, but not directly in the sea. Here, for the first time, we report a strong link between PPP and CDOM in a study carried out in coastal marine waters around Barcelona (NW Mediterranean) in contrasting seasons. We measured relevant correlations between a254 CDOM concentration and both PPP (r=0.89, p < 0.001, n=16; r=0.76, p < 0.01, n=10; and r=0.68, p < 0.001, n=26; for summer, winter–spring and both seasons together, respectively) and the specific production rate at optimal light intensity (Pm B; r=0.77, p < 0.001, n=16; r=0.86, p < 0.01, n=10; and r=0.85, p < 0.001, n=26; for the same seasons). Based on our findings, we design a model that predicts PPP very well, using a254 CDOM, water temperature and photosynthetically active radiation (PAR) (R2=0.84, p < 0.001, n=26). Relationships between CDOM concentration parameters (measured at wavelengths of 280, 300, 340, 355, 375, 412 and 460 nm) and variables associated to CDOM processes (chlorophyll-a, bacterial abundance, turbidity related to sediment resuspension and PAR) were also evaluated. Bacterial abundance is significantly correlated with CDOM concentration measured at higher wavelengths when all samples are considered (e.g., r=0.82, p < 0.001, n=26, for a355 CDOM). However, in seasonal data analysis, the correlations decrease slightly (summer season: e.g., r=0.79, p < 0.001, n=16, for a355 CDOM) or become non-significant (winter– spring season: e.g., r=-0.02, p=0.95, n=10, for a355 CDOM). Sunlight photobleaching and sediment resuspension processes significantly influence CDOM dynamics in the summer (for a300 CDOM: r=-0.72, p < 0.001, n=16; and r=0.67, p < 0.01, n=16, respectively).
Paraules clau: Phytoplankton primary production Carbon uptake CDOM production Bacteria Photodegradation Sediment resuspension
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Gupta M., Gabarro C., Turiel A., Portabella M., Martinez J. (2019)
Journal of Glaciology, 65, (251), 481-493. DOI: 10.1017/jog.2019.26. (BibTeX: gupta.etal.2019a)
Resum: Veure
Arctic sea ice is going through a dramatic change in its extent and volume at an unprecedented rate. Sea-ice thickness (SIT) is a controlling geophysical variable that needs to be understood with greater accuracy. For the first time, a SIT-retrieval method that exclusively uses only airborne SIT data for training the empirical algorithm to retrieve SIT from Soil Moisture Ocean Salinity (SMOS) brightness temperature (TB) at different polarization is presented. A large amount of airborne SIT data has been used from various field campaigns in the Arctic conducted by different countries during 2011–15. The algorithm attempts to circumvent the issue related to discrimination between TB signatures of thin SIT versus low sea-ice concentration. The computed SIT has a rms error of 0.10 m, which seems reasonably good (as compared to the existing algorithms) for analysis at the used 25 km grid. This new SIT retrieval product is designed for direct operational application in ice prediction/climate models.
Paraules clau: Remote sensing; Sea ice; Laser altimetry; Electromagnetic induction; Ice thickness measurements
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Hackert E.C., Kovach R.M., Busalacchi A.J., Ballabrera-Poy J. (2019)
Journal of Geophysical Research: Oceans, 124, 7, 4546-4556. DOI: http://dx.doi.org/10.1029/2019JC015130. (BibTeX: hackert.etal.2019)
Resum: Veure
This study demonstrates the positive impact of including gridded Aquarius and Soil Moisture, Active/Passive (SMAP) sea surface salinity (SSS) into initialization of intermediate complexity coupled model forecasts for the tropical Indo‐Pacific. An experiment that assimilates conventional ocean observations serves as the control. In a separate experiment, Aquarius and SMAP satellite SSS are additionally assimilated into the coupled model initialization. Analysis of the initialization differences with the control indicates that SSS assimilation causes a freshening and shallowing of the mixed layer depth near the equator and enhanced Kelvin wave amplitude. For each month from September 2011 to September 2017, 12‐month‐coupled ENSO forecasts are initialized from both the control and satellite SSS assimilation experiments. The experiment assimilating Aquarius and SMAP SSS significantly outperforms the control relative to observed NINO3.4 sea surface temperature anomalies. This work highlights the potential importance of inclusion of satellite SSS for improving the initialization of operational ENSO coupled forecasts.
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Hernández-Guerra A., Talley L.D., Pelegrí J.L., Vélez-Belchí P., Baringer M.O., Macdonald A.M., McDonagh E.L. (2019)
Progress in Oceanography, 176 DOI: 10.1016/j.pocean.2019.102136. (BibTeX: hernandezguerra.etal.2019)
Resum: Veure
Mass transports for the thermocline, intermediate, deep and abyssal layers in the Atlantic Ocean, at 30°S and for 2003 and 2011, have been estimated using data from GO-SHIP hydrographic transoceanic sections and applying three inverse models with different constraints. The uppermost layers comprise South Atlantic Central Water (SACW) and Antarctic Intermediate Water (AAIW), with a net northward transport in the range of 12.1–14.7 Sv in 2003 and 11.7–17.7 Sv in 2011, which can be considered as the northward returning limb of the Meridional Overturning Circulation (MOC). The western boundary Brazil Current transports twice as much SACW in 2003 (−20.2 ± 0.7 Sv) than in 2011 (−9.7 ± 0.7 Sv). A poleward current consisting of AAIW and Upper Circumpolar Deep Water (UCDW) flows beneath the Brazil Current. The eastern boundary Benguela Current, characterized by a high mesoscale eddy activity, transports 15.6 ± 0.9 Sv in 2003 and 11.2 ± 0.8 Sv in 2011, east of the Walvis Ridge. In the ocean interior, the northward flow is mainly located east of the Mid Atlantic Ridge (MAR) where Agulhas Rings (ARs), observed in both 2003 and 2011, transport warm and salty water from the Indian to the Atlantic Ocean. For the deep layers, the southward transport of North Atlantic Deep Water (NADW) occurs as the Deep Western Boundary Current and also in the eastern basin. The western and eastern basins transport similar amounts of NADW to the south during both years, although the eastern pathway changes substantially between both years. The total NADW transport, which is also considered the MOC, is in the range 16.3–24.5 Sv in 2003 and 17.1–29.6 Sv in 2011, hence with no significant change.
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Lavergne T., Sorensen A.M., Kern S., Tonboe R., Notz D., Aaboe S., Bell L., Dybkjaer G., Eastwood S., Gabarró C., Heygster G., Killie M.A., Kreiner M.B., Lavelle J., Saldo R., Sandven S., Pedersen LT. (2019)
The Cryosphere, 13, 49-78. DOI: 10.5194/tc-13-49-2019. (BibTeX: lavergne.etal.2019a)
Resum: Veure
We introduce the OSI-450, the SICCI-25km and the SICCI-50km climate data records of gridded global seaice concentration. These three records are derived from passive microwave satellite data and offer three distinct advantages compared to existing records: first, all three records provide quantitative information on uncertainty and possibly applied filtering at every grid point and every time step. Second, they are based on dynamic tie points, which capture the time evolution of surface characteristics of the ice cover and accommodate potential calibration differences between satellite missions. Third, they are produced in the context of sustained services offering committed extension, documentation, traceability, and user support. The three records differ in the underlying satellite data (SMMR & SSM/I & SSMIS or AMSR-E & AMSR2), in the imaging frequency channels (37 GHz and either 6 or 19 GHz), in their horizontal resolution (25 or 50 km), and in the time period they cover. We introduce the underlying algorithms and provide an evaluation. We find that all three records compare well with independent estimates of sea-ice concentration both in regions with very high sea-ice concentration and in regions with very low sea-ice concentration. We hence trust that these records will prove helpful for a better understanding of the evolution of the Earth’s sea-ice cover.
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Lin W., Portabella M., Foti G., Stoffelen A., Gommenginger C., He Y. (2019)
IEEE Transactions on Geoscience and Remote Sensing, 57, 2, 655-666. DOI: 10.1109/TGRS.2018.2859191. (BibTeX: lin.etal.2019b)
Resum: Veure
This paper presents a comprehensive procedure to improve the wind geophysical model function (GMF) for the Global Navigation Satellite System Reflectometry (GNSS-R) instrument onboard the TechDemoSat-1 satellite. The observable used to define the GMF is extracted from the measured delay- Doppler maps (DDMs) by correcting for the nongeophysical effects within the measurements. Besides the instrument and the geometric effects as provided in the bistatic radar equation, a calibration term that accounts for the uncalibrated receiver antenna gain and the unknown transmitter antenna gain is proposed to optimize the calculation of GNSS-R observables. Such calibration term is presented as a function of observing elevation and azimuth angles and is shown to remarkably reduce the measurement uncertainties. First, an empirical wind-only GMF is developed using the collocated Advanced Scatterometer (ASCAT) winds and European Centre for Medium-Range Weather Forecasts (ECMWF) model wind output. This empirical GMF agrees well with the model output. Then, the sensitivity of the observable to waves is analyzed using the collocated ECMWF wave parameters. The results show that it is difficult to include mean square slope (MSS) in the development of an empirical GMF, since the difference between ECMWF MSS and the MSS sensed by GNSS-R varies with incidence angle and wind speed. However, it is relevant to take significant wave height (Hs) in account, particularly for low wind conditions. Consequently, a wind/Hs approach is proposed for improved wind retrievals.
Paraules clau: Advanced Scatterometer (ASCAT); Calibration; Global Navigation Satellite System Reflectometry (GNSS-R); Wave; Winds
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Lin W., Dong X., Portabella M., Lang S., He Y., Yun R., Wang Z., Xu X., Zhu D., Liu J. (2019)
IEEE Transactions on Geoscience and Remote Sensing, 57, 2, 627-639. DOI: 10.1109/TGRS.2018.2858852. (BibTeX: lin.etal.2019c)
Resum: Veure
The China-France Oceanography Satellite (CFOSAT) to be launched in October 2018 will carry two innovative payloads, i.e., the surface wave investigation and monitoring instrument and the rotating fan-beam scatterometer [CFOSAT scatterometer (CFOSCAT)]. Both instruments, operated in Ku-band microwave frequency, are dedicated to the measurement of sea surface wave spectra and wind vectors, respectively. This paper provides an overview of the system definition and characteristics of the CFOSCAT instrument. A prelaunch analysis is carried out to estimate the scatterometer backscatter and wind quality based on the developed CFOSCAT simulator prototype. The overall simulation includes two parts: first, a forward model is developed to simulate the ocean backscatter signals, accounting for both instrument and geophysical noise. Second, a wind inversion processor is used to retrieve wind vectors from the outputs of the forward model. The benefits and challenges of the novel observing geometries are addressed in terms of the CFOSCAT wind retrieval. The simulations show that the backscatter accuracy and the retrieved wind quality of CFOSCAT are quite promising and meet the CFOSAT mission requirements.
Paraules clau: Backscatter; Inversion; Measurement errors; Remote sensing; Rotating fan-beam scatterometer; Simulation; Wind.
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Madurell T., Spencer-Jones M., Zabala M. (2019)
European Journal of Taxonomy, 536, 1-33. DOI: 10.5852/ejt.2019.536. (BibTeX: madurell.etal.2019a)
Resum: Veure
We examined the type specimens and historical collections holding puzzling Atlantic and Mediterranean material belonging to the genus Schizoretepora Gregory, 1893. We performed a detailed study of the colonial characters and re-describe the resulting species and those that have rarely been found or have poor original descriptions. As a result of this revision, nine species are found in the northeast Atlantic and Mediterranean. Six of them are re-described and illustrated: S. aviculifera (Canu & Bassler, 1930), S. calveti d’Hondt, 1975, S. imperati (Busk, 1884), S. sp. nov.? (= S. imperati sensu O’Donoghue & de Watteville 1939) (in open nomenclature, specimen lacks ovicells), S. pungens (Canu & Bassler, 1928) and S. solanderia (Risso, 1826). For S. dentata (Calvet, 1931), no material remains; furthermore, S. hassi Harmelin, Bitar & Zibrowius, 2007 and S. serratimargo (Hincks, 1886) have recently been described and redescribed, respectively. This new arrangement attains a coherent geographical distribution: S. imperati seems restricted to the eastern Atlantic, S. dentata and S. calveti are deepwater species from Atlantic islands, S. pungens and S. aviculifera dwell on the African coasts of the Western Mediterranean, S. hassi and S. sp. nov.? (=S. imperati sensu O’Donogue & de Wateville 1939) are confi ned to the Eastern Mediterranean, and S. solanderia and S. serratimargo live on the European coasts of the Mediterranean.
Paraules clau: Phidoloporidae; Taxonomy
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Martínez-Pérez A.M., Catalá T.S., Nieto-Cid M., Otero J., Álvarez M., Emelianov M., Reche I., Álvarez-Salgado X.A., Arístegui J. (2019)
Progress in Oceanography, 70, 93-106. DOI: 10.1016/j.pocean.2018.10.019. (BibTeX: martinezperez.etal.2019a)
Resum: Veure
Fluorescent dissolved organic matter (FDOM) in the Mediterranean Sea was analysed by excitation–emission matrix (EEM) spectroscopy and parallel factor (PARAFAC) analysis during the cruise HOTMIX 2014. A 4–component model, including 3 humic–like and 1 protein–like compounds, was obtained. To decipher the environmental factors that dictate the distributions of these components, we run generalized additive models (GAMs) in the epipelagic layer and an optimum multiparametric (OMP) water masses analysis in the meso– and bathypelagic layers. In the epipelagic layer, apparent oxygen utilization (AOU) and temperature presented the most significant effects on the variability of the marine humic-like peak M fluorescence, suggesting that its distribution was controlled by the net community respiration of organic matter and photobleaching. On the contrary, the variability of the soil humic-like peak E and the protein–like peak T fluorescence was explained mainly by the prokaryotic heterotrophic abundance, which decreased eastwards. In the meso– and bathypelagic layers, water mass mixing and basin–scale mineralization processes explained > 72% and 63% of the humic–like and protein–like fluorescence variability, respectively. When analysing the two basins separately, the OMP model offered a better explanation of the distribution of fluorescence in the eastern Mediterranean Sea, as expected from the reduced biological activity in this ultra–oligotrophic basin. Furthermore, while western Mediterranean deep waters display the usual trend in the global ocean (increase of humic–like fluorescence and decrease of protein–like fluorescence with higher AOU values), the eastern Mediterranean deep waters presented an opposite trend. Different initial fluorescence intensities of the water masses that mix in the eastern basin, with Adriatic and Aegean origins, seem to be behind this contrasting pattern. The analysis of the transect–scale mineralization processes corroborate this hypothesis, suggesting a production of humic–like and a consumption of protein–like fluorescence in parallel with water mass ageing. Remarkably, the transect–scale variability of the chromophoric dissolved organic matter (CDOM) absorbing at the excitation wavelength of the humic–like peak M indicates an unexpected loss with increasing AOU, which suggests that the consumption of the non–- fluorescent fraction of CDOM absorbing at that wavelength exceeded the production of the fluorescent fractionobserved here.
Paraules clau: Dissolved organic matter; Fluorescence spectroscopy; PARAFAC; Water mass analysis; Mediterranean Sea
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Martín-Rey M., Lazar A. (2019)
Climate Dynamics, 53, 2339-2353. DOI: 10.1007/s00382-019-04851-9. (BibTeX: martinrey.lazar.2019a)
Resum: Veure
The Equatorial Mode (EM) governs the tropical Atlantic inter-annual variability during boreal summer. It has profound impacts on the climate of adjacent and remote areas. However, predicting the EM is one of the most challenging and intriguing issues for the scientifc community. Recent studies have suggested a possible connection between the boreal spring Meridional Mode (MM) and the EM through ocean wave propagation. Here, we use a set of sensitivity experiments with a medium-resolution ocean model to determine the precursor role of a MM to create equatorial SST variability. Our results demonstrate that boreal summer equatorial SSTs following a MM, are subject to two counteracting efects: the local wind forcing and remotely-excited oceanic waves. For a positive MM, the anomalous easterly winds blowing along the equator, shallow the thermocline, cooling the sea surface via vertical difusion and meridional advection. Anomalous wind curl excites a downwelling Rossby wave north of equator, which is refected at the western boundary becoming an equatorial Kelvin wave (KW). This downwelling KW propagates eastward, deepening the thermocline and activating the thermocline feedbacks responsible for the equatorial warming. Moreover, the local wind forcing and RW-refected mechanism have a signifcant and comparable impact on the equatorial SST variability. Changes in the intensity and persistence of these distinct forcings will determine the equatorial SST response during boreal summer. Our results give a step forward to the improvement of the EM predictability.
Paraules clau: Tropical Atlantic; Meridional Mode; Equatorial Mode; Ocean waves; SST variability
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Merkowitz S.M., Bolotin S., Elosegui P., Esper J., Gipson J., Hilliard L., Himwich E., Hoffman E.D., Lakins D.D., Lamb R.C., Lemoine F.G., Long J.L., McGarry J.F., MacMillan D.S., Michael B.P., Noll C., Pavlis E.C., Pearlman M.R., Ruszczyk C., Shappirio M.D., Stowers D.A. (2019)
Journal of Geodesy, 93, 11, 2263-2273. DOI: 10.1007/s00190-018-1204-5. (BibTeX: merkowitz.etal.2019a)
Resum: Veure
NASA maintains and operates a global network of Very Long Baseline Interferometry (VLBI), Satellite Laser Ranging (SLR), and Global Navigation Satellite System ground stations as part of the NASA Space Geodesy Program. The NASA Space Geodesy Network (NSGN) provides the geodetic products that support Earth observations and the related science requirements as outlined by the US National Research Council (NRC in Precise geodetic infrastructure: national requirements for a shared resource, National Academies Press, Washington, 2010. http://nap.edu/12954, Thriving on our changing planet: a decadal strategy for Earth observation from space, National Academies Press, Washington, 2018. http://nap.edu/24938). The Global Geodetic Observing System (GGOS) and the NRC have set an ambitious goal of improving the Terrestrial Reference Frame to have an accuracy of 1 mm and stability of 0.1 mm per year, an order of magnitude beyond current capabilities. NASA and its partners within GGOS are addressing this challenge by planning and implementing modern geodetic stations colocated at existing and new sites around the world. In 2013, NASA demonstrated the performance of its next-generation systems at the prototype next-generation core site at NASA’s Goddard Geophysical and Astronomical Observatory in Greenbelt, Maryland. Implementation of a new broadband VLBI station in Hawaii was completed in 2016. NASA is currently implementing new VLBI and SLR stations in Texas and is planning the replacement of its other aging domestic and international legacy stations. In this article, we describe critical gaps in the current global network and discuss how the new NSGN will expand the global geodetic coverage and ultimately improve the geodetic products. We also describe the characteristics of a modern NSGN site and the capabilities of the next-generation NASA SLR and VLBI systems. Finally, we outline the plans for efficiently operating the NSGN by centralizing and automating the operations of the new geodetic stations
Paraules clau: Space Geodesy; Terrestrial Reference Frame; ITRF; VLBI; SLR; GNSS; DORIS
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Nunes S., Latasa M., Delgado M., Emelianov M., Simó R., Estrada M. (2019)
Deep-Sea Research. Part I: Oceanographic Research Papers, 151, 103059 DOI: 10.1016/j.dsr.2019.06.005. (BibTeX: nunes.etal.2019a)
Resum: Veure
The relationships between taxonomy and distribution of the phytoplankton and environmental parameters were studied in four contrasting zones (North of the South Orkney Islands= NSO, Southeast of the South Orkney Islands = SSO, Northwest of South Georgia = NSG and West of Anvers = WA) of the Atlantic sector of the Southern Ocean, during the PEGASO cruise of the BIO Hespérides (January–February 2015). The structure of the phytoplankton community was determined by microscopic examination and by pigment analyses using highperformance liquid chromatography (HPLC) followed by application of the CHEMTAX algorithm. Overall, a statistically significant association was found between fluorometric and HPLC determinations of chlorophyll a, and between chemotaxonomic and microscopy-derived estimates of the contribution of diatoms, dinoflagellates and cryptophytes, although cryptophytes appeared to be underestimated by the microscopic observations. The highest average levels of fluorometric chlorophyll a (517 mg m−2 ) were found at NSG, followed by WA (132 mg m−2 ), NSO (120 mg m−2 ) and SSO (34 mg m−2 ). The phytoplankton community at NSG was dominated by diatoms like Eucampia antarctica and Thalassiosira spp. Cryptophytes and diatoms (mainly Corethron pennatum, small Thalassiosira spp. and Fragilariopsis spp.) were the most abundant chemotaxonomic groups at NSO, followed by haptophytes types 6 + 7, Phaeocystis-like (haptophytes type 8) and, especially in the deeper levels of the euphotic zone, pelagophytes. At SSO, the most important groups were haptophytes types 6 + 7, followed by diatoms (with a combination of taxa similar to that of NSO), Phaeocystis-like and pelagophytes. The main CHEMTAX groups at WA were cryptophytes (between surface and about 40 m depth), haptophytes types 6 + 7 and diatoms. The ratio between the photoprotective pigment diadinoxanthin and the sum of the light harvesting pigments of diadinoxanthin-containing phytoplankton (sum of 19′-butanoyloxyfucoxanthin, 19′-hexanoyloxyfucoxanthin, fucoxanthin and peridinin) was highest at SSO, indicating exposure to a high irradiance environment, and presented a significant positive correlation with the euphotic zone depth. The ratios of the algal osmolyte dimethylsulfoniopropionate and the trace gas dimethylsulfide to chlorophyll a showed the same pattern across zones, highlighting the role of light-related ecophysiology in combination with taxonomy in regulating the production of dimethylated sulfur by plankton communities.
Paraules clau: Southern ocean; Phytoplankton distribution; Microscopy; HPLC; CHEMTAX; Pigments; Dimethylated sulfur
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Olmedo E., González-Gambau V., Turiel A., Martínez J., Gabarró C., Portabella M., Ballabrera-Poy J., Arias M., Sabia R., Oliva R. (2019)
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 12, 7, 2486 - 2503. DOI: 10.1109/JSTARS.2019.2904947. (BibTeX: olmedo.etal.2019c)
Resum: Veure
After more than eight years of the European Space Agency (ESA) Soil Moisture and Ocean Salinity (SMOS) acquisitions, an exhaustive, empirical characterization of the biases and uncertainties affecting SMOS brightness temperatures over the ocean is possible. We show that both parameters strongly depend not only on the position in the field of view, but also on the geographical location of the acquisition. Metrics based on the differences between expected and theoretical values of the bias and the uncertainty are developed and used for quantitatively assessing the locations where SMOS errors are currently not accurately characterized. This characterization can be used for the definition of a new empirical SMOS sea surface salinity (SSS) bias correction, a better cost function retrieval, and more accurate filtering criteria, which are expected to lead to a better SMOS SSS Level 2 product. We present a new L2 SMOSSSS product based on the described investigation. The performance of this preliminary product is similar to that of the version v662 of the official L2 SMOS SSS product at medium and low latitudes. However, it provides a better coverage at high latitudes and coastal regions affected by radio frequency interference (RFI), which correspond to those regions where the SMOS errors are currently poorly estimated.
Paraules clau: Brightness temperature (TB) biases, brightness temperature uncertainty, coastal areas, radio frequency interference (RFI), sea surface salinity (SSS), Soil Moisture and Ocean Salinity (SMOS).
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Orué-Echevarría D., Pelegrí J.L., Alonso-González I.J., Benítez-Barrios V.M., De La Fuente P., Emelianov M., Gasser M., Herrero C., Isern-Fontanet J., Peña-Izquierdo J., Ramírez-Garrido S., Rosell-Fieschi M., Salvador J., Saraceno M., Valla D., Vidal M. (2019)
Data in Brief, 22, 185–194. DOI: 10.1016/j.dib.2018.12.004. (BibTeX: orueechevarria.etal.2019b)
Resum: Veure
This oceanographic dataset was gathered during the TIC-MOC cruise, which was designed to characterize the dynamics of the Brazil-Malvinas Confluence. The cruise was carried on board the R/V Hespérides ,with departure from Ushuaia and arrival to Salvador de Bahía. A total of 66 conductivity-temperature-depth (CTD) stations were completed between 8 and 22 March 2015, offshore from the continental platform and within 45°S-35°S and 61°W-50°W. At each station, water samples were collected, which were used to calibrate the CTD salinity-oxygen sensors and to determine inorganic nutrient concentrations, and the horizontal current was measured. Along its track, the vessel recorded surface temperature and salinity, as well as the horizontal flow down to about 700 m. Lastly, eight position-transmitting drifters were launched and two profiling
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Orué-Echevarría D., Pelegrí J.L., Machín F., Hernández-Guerra A., Emelianov M. (2019)
Journal of Geophysical Research: Oceans, 124, 1, 527-554. DOI: 10.1029/2018JC014733. (BibTeX: orueechevarria.etal.2019d)
Resum: Veure
The Brazil‐Malvinas Confluence arises from the frontal encountering of the subtropical Brazil Current and subantarctic Malvinas Current. It displays a complex regional circulation that is accompanied by mesoscale features and thermohaline intrusions. Here we combine altimetry and cruise data to describe the circulation pattern in the upper 2,000 m at two spatial scales encircling the frontal system. The major regional features appear south of the confluence latitude at 39–40°S: (a) a relatively weak Malvinas Current near 41°S, 56°W (28.3 ± 1.4 Sv), followed by its cyclonic retroflection; (b) an intense subtropical anticyclone (59.3 ± 10.7 Sv) that replaces the Brazil Current overshoot; and (c) a very intense subantarctic inflow (78.9 ± 13.7 Sv) near 53°W that is maintained through both an upstream (near 42°S) earlier diversion of the Malvinas Current and the cyclonic recirculation of the flow exiting east along the confluence. North of the confluence, the Brazil Current provides a net input of 30.8 ± 12.0 Sv (29.1 ± 8.3 Sv along the slope). The southern inflow splits nearly equal between barotropic and baroclinic contributions while the entire northern flow is essentially baroclinic. These northern and southern inputs add to an eastward along‐front transport of 109.7 ± 15.1 Sv, with significant contribution of highly oxygenated, relatively fresh Subantarctic Mode and Antarctic Intermediate Waters (58.7 ± 5.6 Sv). The regional circulation experiences substantial temporal variability, with southern waters flowing into the Brazil‐Malvinas Confluence through along‐slope and interior pathways and partly recirculating within the subtropical South Atlantic gyre.
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Orué-Echevarría D., Castellanos P., Sans J., Emelianov M., Vallès-Casanova I., Pelegrí J.L. (2019)
Geophysical Research Letters, 46, 22, 13234-13243. DOI: 10.1029/2019GL084246. (BibTeX: orueechevarria.etal.2019e)
Resum: Veure
Ocean frontal systems may act both as barriers and mixers between different water masses, the latter thanks to very energetic structures with relatively short temporal and spatial scales. Here, we explore the high‐frequency temperature variability in the Brazil‐Malvinas Confluence through the joint analysis of novel high‐resolution SeaSoar measurements and sea surface temperature imagery. Surface spatiotemporal correlation scales range between 1.5 and 6 days and between 20 and 50 km, with the shortest scales along the shelf‐break path of the Brazil Current and over the confluence and the longest ones along the Malvinas Current. The spatial scales display minima along the front, at the surface because of the presence of brackish shelf waters and at the subsurface due to both mesoscale and submesoscale thermohaline intrusions. The smallest cross‐frontal vertical correlations, in the 5‐ to 10‐m range, are associated with submesoscale processes. Overall, temperature variability is enhanced at depth in the frontal system.
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Pelegrí J.Ll. (2019)
Treballs de la Societat Catalana de Biologia, 69, 41-48. DOI: 10.2436/20.1501.02.181. (BibTeX: pelegri.2019a)
Resum: Veure
[EN] Ocean ecosystems and currents as subsystems of a planetary organismplanetary organism. The oceans are origin and instrument for the life of a planet that, paradoxically, we call Earth. The oceans keep most of the water and other properties that flow in the cycle of life, all of them conditioned by the energy that comes from the Sun. This insolation reaches the surface waters according to latitude and time, and it is incorporated and distributed through the oceans as heat and mechanical and chemical energy. During the processes of incorporation and transformation, the thermodynamic and dynamic conditions of the regional habitats are defined, which give rise to biogeochemical properties and typical communities, and the ocean currents, with a broad range of temporal patterns and spatial structures, shape a circulatory system analogous to other living organisms. A complex network of subsystems with complementary tasks is established: the great planetary organism emerges! [CAT] Els oceans són origen i instrument per a la vida del planeta que, paradoxalment, anomenem Terra. Els oceans guarden la major part de l’aigua i altres propietats que flueixen en el cicle de la vida, totes elles condicionades per l’energia que ens ve del Sol. Aquesta insolació arriba a les aigües superficials en funció de la latitud i el temps, i s’incorpora i distribueix pels oceans en forma de calor i energia mecànica i química. Durant els processos d’incorporació i transformació, es defineixen les condicions termodinàmiques i dinàmiques dels hàbitats regionals, que donen peu a característiques biogeoquímiques i comunitats pròpies, i són els corrents oceànics els que, amb tot un ventall de patrons temporals i d’estructures espacials, conformen un sistema circulatori anàleg al d’altres éssers vius. S’estableix una xarxa complexa de subsistemes amb tasques complementàries: sorgeix el gran organisme planetari!
Paraules clau: Carbon budgets; Greenhouse effect; Atmospheric composition; Climate change; Balanços de carboni; Efecte d’hivernacle; Composició atmosfèrica; Canvi climàtic
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Pennino M.G., Bevilacqua A.H., Torres M.A., Bellido J.M., Solé J., Steenbeek J., Coll M. (2019)
Marine Policy, 116, 103703 DOI: 10.1016/j.marpol.2019.103703. (BibTeX: pennino.etal.2019)
Resum: Veure
Discarding is one of the most important topics in fisheries management, both for economic and ecological reasons. The European Union has included, through the current EU Common Fisheries Policy (CFP) Regulation, a discard ban with a quite controversial instrument: to enforce the landing of unwanted catch as a measure to promote their reduction. This management decision may condition the future of the fishing exploitation in European Sea. Within this context, both stakeholders and policy makers are now claiming for more effective tools that can be used to support the decision-making framework. In this study, we propose a simulation-based approach combining hierarchical Bayesian Spatial Models (H-BSMs) with the spatial-temporal module of Ecopath with Ecosim (EwE) approach, Ecospace, in the North Western Mediterranean Sea. In particular, we firstly assessed high-density discard areas using H-BSMs with fisheries and environmental data, and secondly, we simulated potential management options to identify the trade-offs of the discard ban application within these areas using EwE. We argue that coupling novel methods, as the ones used in this study, could be a decisive step to identify the best management action among a set of different scenarios within the context of the discard ban application in European Seas.
Paraules clau: Bayesian model Discards Ecospace Food web model Landing obligation Mediterranean sea Spatial ecology
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Piles M., Ballabrera-Poy J., Muñoz-Sabater J. (2019)
Remote Sensing, 11, 95 DOI: 10.3390/rs11010095. (BibTeX: piles.etal.2019a)
Resum: Veure
Soil moisture observations are expected to play an important role in monitoring global climate trends. However, measuring soil moisture is challenging because of its high spatial and temporal variability. Point-scale in-situ measurements are scarce and, excluding model-based estimates, remote sensing remains the only practical way to observe soil moisture at a global scale. The ESA-led Soil Moisture and Ocean Salinity (SMOS) mission, launched in 2009, measures the Earth’s surface natural emissivity at L-band and provides highly accurate soil moisture information with a 3-day revisiting time. Using the first six full annual cycles of SMOS measurements (June 2010–June 2016), this study investigates the temporal variability of global surface soil moisture. The soil moisture time series are decomposed into a linear trend, interannual, seasonal, and high-frequency residual (i.e., subseasonal) components. The relative distribution of soil moisture variance among its temporal components is first illustrated at selected target sites representative of terrestrial biomes with distinct vegetation type and seasonality. A comparison with GLDAS-Noah and ERA5 modeled soil moisture at these sites shows general agreement in terms of temporal phase except in areas with limited temporal coverage in winter season due to snow. A comparison with ground-based estimates at one of the sites shows good agreement of both temporal phase and absolute magnitude. A global asseSMent of the dominant features and spatial distribution of soil moisture variability is then provided. Results show that, despite still being a relatively short data set, SMOS data provides coherent and reliable variability patterns at both seasonal and interannual scales. Subseasonal components are characterized as white noise. The observed linear trends, based upon one strong El Niño event in 2016, are consistent with the known El Niño Southern Oscillation (ENSO) teleconnections. This work provides new insight into recent changes in surface soil moisture and can help further our understanding of the terrestrial branch of the water cycle and of global patterns of climate anomalies. Also, it is an important support to multi-decadal soil moisture observational data records, hydrological studies and land data assimilation projects using remotely sensed observations.
Paraules clau: SMOS; Soil moisture; Climatology; Trends; Signal decomposition
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Quintanilla E., Madurell T., Wilke T., Sánchez J.A. (2019)
Frontiers in Marine Science, 6, 694 DOI: 10.3389/fmars.2019.00694. (BibTeX: quintanilla.etal.2019a)
Resum: Veure
Gorgonian corals occurring in shallow waters are vulnerable to changing environmental conditions and human-related pressures such as pollution, overfishing, and diseases. However, anthropogenic effects on coral systems are difficult to quantify due to the lack of base-line data of unaffected populations. In order to assess the impact of global and local environmental parameters on gorgonian populations removed from direct anthropogenic impact, we evaluated demographic parameters and the health status of Pacifigorgia cairnsi (Gorgoniidae: Octocorallia) populations in Malpelo Island, a remote and pristine marine area in the Tropical Eastern Pacific of Colombia. Specifically, we studied P. cairnsi densities and population size structures under different habitat and local environmental conditions. We also studied whether ENSO events and local hydrodynamic features including locality, water depth, and upwelling conditions drive P. cairnsi growth rates. Finally, we evaluated the prevalence of the necrotic patch disease and rates of disease recovery. Major findings were that local hydrodynamic parameters shaped P. cairnsi size structures, that growth rates were affected by thermal anomalies associated to ENSO events and partly by water depth, that overall disease prevalence was low (6%) and that it did not correlate with the environmental parameters studied, and that most diseased colonies (57%) recovered via tissue breakage. The fact that P. cairnsi, a keystone species within the regional benthic food web, is affected by thermal anomalies remains of concern because these global events are predicted to increase in frequencies and severity in the future. Nonetheless, the low level of disease prevalence found indicates that the island’s pristine conditions might facilitate disease resistance. Moreover, the findings suggest an interesting trade-off between growth rates and colony recovery in shallow waters related to tissue breakage. This study provides crucial base-line data for future investigations aiming at understanding coral responses to anthropogenic pressures and the impact of global climate change on coral communities.
Paraules clau: Gorgonian corals; Tropical Eastern Pacific; Disease prevalence; Growth rates; ENSO
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Raj R.P., Chatterjee S., Bertino L., Turiel A., Portabella M. (2019)
Ocean Science, 15, 1729-1744. DOI: 10.5194/os-15-1729-2019. (BibTeX: raj.etal.2019a)
Resum: Veure
The Arctic Front (AF) in the Norwegian Sea is an important biologically productive region which is wellknown for its large feeding schools of pelagic fish. A suite of satellite data, a regional coupled ocean–sea ice data assimilation system (the TOPAZ reanalysis) and atmospheric reanalysis data are used to investigate the variability in the lateral and vertical structure of the AF. A method, known as “singularity analysis”, is applied on the satellite and reanalysis data for 2-D spatial analysis of the front, whereas for the vertical structure, a horizontal gradient method is used. We present new evidence of active air–sea interaction along the AF due to enhanced momentum mixing near the frontal region. The frontal structure of the AF is found to be most distinct near the Faroe Current in the south-west Norwegian Sea and along the Mohn Ridge. Coincidentally, these are the two locations along the AF where the air–sea interactions are most intense. This study investigates in particular the frontal structure and its variability along the Mohn Ridge. The seasonal variability in the strength of the AF is found to be limited to the surface. The study also provides new insights into the influence of the three dominant modes of the Norwegian Sea atmospheric circulation on the AF along the Mohn Ridge. The analyses show a weakened AF during the negative phase of the North Atlantic Oscillation (NAO-), even though the geographical location of the front does not vary. The weakening of AF during NAO- is attributed to the variability in the strength of the Norwegian Atlantic Front Current over the Mohn Ridge associated with the changes in the wind field.
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Romera-Castillo C., Álvarez M., Pelegrí J.L., Hansell D.A., Álvarez-Salgado X.A. (2019)
Global Biogeochemical Cycles, 33, 9, 1162-1173. DOI: 10.1029/2018GB006162. (BibTeX: romeracastillo.etal.2019)
Resum: Veure
Most dissolved organic carbon (DOC) sequestered in the deep ocean has residence times of decades to thousands of years, with clear implications for climate regulation, though some net removal is typically observed with increasing water mass age. Here, a high‐quality‐high‐resolution data set has allowed us to identify net additions of recalcitrant DOC in specific water masses of the deep South Atlantic. Overall, the South Atlantic is a net source of recalcitrant DOC, adding 0.027 ± 0.019 Pg C/year, while the North Atlantic is a net sink that removes 0.298 ± 0.141 Pg C/year. We find that the balance of addition/removal of recalcitrant DOC depends not only on the origin but also on the temperature, age, and depth of the water masses that circulate and mix in the Atlantic Ocean. Future changes in the water mass composition and circulation patterns due to climate change would eventually affect that balance, altering the carbon cycle.
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Salat J., Pascual J., Flexas M., Chin T.M., Vazquez-Cuervo J. (2019)
Ocean Dynamics, 69, 1067–1084. DOI: 0.1007/s10236-019-01285-z. (BibTeX: salat.etal.2019)
Resum: Veure
Marine and atmospheric parameters, including temperature observations from surface to 80 m (at 6 depths) are measured sinceSeptember 1973 on a higher-than-weekly frequency, at a coastal station 4 km offshore L’Estartit (Costa Brava; NWMediterranean). This constitutes the longest available uninterrupted oceanographic time series in the Mediterranean Sea. Thepresent contribution focuses on observed climatic trends in temperature (°C/year) of air (AT; 0.05), sea surface (SST; 0.03), sea at80 m depth (S80T; 0.02) and sea level (SL; 3.1 mm/year) as well as comparison with trends estimated from coincident high-resolution satellite data. The trending evolution is not uniform across seasons, being significantly higher in spring for both ATandSST, while in autumn for S80T. Other climatological results are a stratification increase (0.02 °C/year in summer temperaturedifference between 20 m (S20T) and S80T), trends in summer conditions at sea (when S20T > 18 °C), estimated as 0.5 and0.9 days/year for the starting day and period respectively, and a decreasing trend of nearly 2 days/year in the period of conditionsfavourable for marine evaporation (when AT < SST). This last trend may be related to the observed decrease of coastalprecipitation in spring. The long-term consistency in the in situ SST measurements presents an opportunity to validate themulti-decadal trends. The good agreement for 2013–2018 (RMS 0.5–0.6, bias−0.1 to−0.2; trends of 0.09 °C/year in situ vs.0.06 to 0.08 °C/year from satellite) allows considering this observational site as ground truth for satellite observations and amonitoring site for climate change
Paraules clau: Oceanographic time series.Climate trends.Satellite ground truth.Stratification.Seasonality.Mediterranean Sea
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Torres G., Carnicer O., Canepa A., De La Fuente P., Recalde S., Narea R., Pinto E., Borbor-Córdova M.J. (2019)
Frontiers in Marine Science, 6, 145 DOI: 10.3389/fmars.2019.00145. (BibTeX: torres.etal.2019)
Resum: Veure
Among marine phytoplankton, dinoflagellates are a key component in marine ecosystems as primary producers. Some species synthesize toxins, associated with human seafood poisoning, and mortality in marine organisms. Thus, there is a large necessity to understand the role of environmental variables in dinoflagellates spatialtemporal patterns in response to future climate scenarios. In that sense, a monthly four-year (2013–2017) monitoring was taken to evaluate dinoflagellates abundances and physical-chemical parameters in the water column at different depths. Sampling sites were established at 10 miles in four locations within the Ecuadorian coast. A total of 102 taxa were identified, corresponding to 8 orders, 22 families, and 31 genera. Eight potentially harmful genera were registered but no massive blooms were detected. The most frequent dinoflagellates were Gymnodinium sp. and Gyrodinium sp. Environmental variables showed different mixing layer thickness and a conspicuous and deepening thermocline/oxycline/halocline and nutricline depending on annual and seasonal oceanographic fluctuations. This study confirms that seasonal and spatial distribution of the environmental variables are linked to the main current systems on the Eastern Tropical Pacific, thus the warm Panama current lead to a less dinoflagellates abundance in the north of Ecuador (Esmeraldas), while the Equatorial Upwelling and the cold nutrient-rich Humboldt Current influence dinoflagellates abundance at the central (Manta, La Libertad) and South of Ecuador (Puerto Bolivar), respectively. Interannual variability of dinoflagellates abundance is associated with ENSO and upwelling conditions. Climate change scenarios predict an increase in water surface temperature and extreme events frequency in tropical areas, so it is crucial to involve policy-makers and stakeholders in the implementation of future laws involving long-term monitoring and sanitary programs, not covered at present.
Paraules clau: dinoflagellates, HABs, ENSO, tropical Eastern Pacific, nutrients, upwelling, humboldt current
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Viúdez A. (2019)
Journal of Fluid Mechanics, 859, R1 DOI: 10.1017/jfm.2018.892. (BibTeX: viudez.2019a)
Resum: Veure
Exact solutions for multipolar azimuthal-mode vortices in two-dimensional Euler flows are presented. Flow solutions with non-vanishing far-field velocity are provided for any set of azimuthal wavenumbers m and arbitrary number n of vorticity shells. For azimuthal wavenumbers mD0 and mD1, the far-field velocity is a rigid motion and unsteady flow solutions with vanishing far-field velocity are obtained by means of a time-dependent change of reference frame. Addition of these first two modes, in the case of n = 1, results in a particular Chaplygin–Lamb (C–L) dipole, with continuous and vanishing vorticity at the vortex boundary. Numerical simulations suggest that this particular C–L dipole is stable.
Paraules clau: Vortex dynamics; Vortex flows
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Viúdez A. (2019)
Journal of Fluid Mechanics, 868, R1, 1-13. DOI: 10.1017/jfm.2019.234. (BibTeX: viudez.2019b)
Resum: Veure
An exact solution of a baroclinic three-dimensional vortex dipole in geophysical flows with constant background rotation and constant background stratification is provided under the quasi-geostrophic (QG) approximation. The motion of the dipole is unsteady but the potential vorticity contours move rigidly. The vortex comprises three potential vorticity anomaly modes, with a radial dependence given by the spherical Bessel functions and with azimuthal and polar dependences given by the spherical harmonics. The first mode, or spherical mode, accounts for the horizontal asymmetry of the vortex dipole and curvature of the dipole’s horizontal trajectory. The second mode, or dipolar mode, accounts for the speed of displacement of the vortex dipole. A third mode, or vertical tilting mode, accounts for the dipole’s vertical asymmetry. The QG vertical velocity field has two contributions: the first one is octupolar and depends entirely on the dipolar mode, and the second one is dipolar and depends on the nonlinear interaction between dipolar and vertical tilting modes.
Paraules clau: baroclinic flows, quasi-geostrophic flows, vortex dynamics
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Viúdez A. (2019)
Journal of Fluid Mechanics, 878, R5, 1-11. DOI: 10.1017/jfm.2019.730. (BibTeX: viudez.2019c)
Resum: Veure
An exact solution of a stable vortex tripole in two-dimensional (2-D) Euler flows is provided. The stable tripole is composed of an inner elliptical vortex and two small-amplitude lateral vortices. The non-vanishing vorticity field of this tripole, referred to as here as an embedded tripole because of the closeness of its vortices, is given in elliptical coordinates .; / by the even radial and angular order-0 Mathieu functions Je0./ce0./ truncated at the external branch of the vorticity isoline passing through the two critical points closest to the vortex centre. This tripole mode has a rigid vorticity field which rotates with constant angular velocity equal to 0Je0.1/ce0.0/=2, where 1 is the first zero of Je0 0./ and 0 is a constant modal amplitude. It is argued that embedded 2-D tripoles may be conceptually regarded as the superposition of two asymmetric Chaplygin–Lamb dipoles, separated a distance equal to 2R, as long as their individual trajectory curvature radius R is much shorter than their dipole extent radius.
Paraules clau: vortex dynamics, vortex instability, vortex interactions
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Zamanillo M., Ortega-Retuerta E., Nunes S., Estrada M., Sala M.M., Royer S.-J., López-Sandoval D.C., Emelianov M., Vaqué D., Marrasé C., Simó R. (2019)
Science of The Total Environment, 691, 736-748. DOI: 10.1016/j.scitotenv.2019.06.524. (BibTeX: zamanillo.etal.2019f)
Resum: Veure
Transparent exopolymer particles (TEP) are an abundant class of suspended organic particles, mainly formed by polysaccharides, which play important roles in biogeochemical and ecological processes in the ocean. In this study we investigated horizontal and vertical TEP distributions (within the euphotic layer, including the upper surface) and their short-term variability along with a suite of environmental and biological variables in four distinct regions of the Southern Ocean. TEP concentrations in the surface (4 m) averaged 102.3 ± 40.4 μg XG eq. L−1 and typically decreased with depth. Chlorophyll a (Chl a) concentration was a better predictor of TEP variability across the horizontal (R2 = 0.66, p < 0.001) and vertical (R2 = 0.74, p < 0.001) scales than prokaryotic heterotrophic abundance and production. Incubation experiments further confirmed the main role of phytoplankton as TEP producers. The highest surface TEP concentrations were found north of the South Orkney Islands (144.4 ± 21.7 μg XG eq. L−1), where the phytoplankton was dominated by cryptophytes and haptophytes; however, the highest TEP:Chl a ratios were found south of these islands (153.4 ± 29.8 μg XG eq (μg Chl a)−1, compared to a mean of 79.3 ± 54.9 μg XG eq (μg Chl a)−1 in the whole cruise, in association with haptophyte dominance, proximity of sea ice and high exposure to solar radiation. TEP were generally enriched in the upper surface (10 cm) respect to 4 m, despite a lack of biomass enrichment, suggesting either upward transport by positive buoyancy or bubble scavenging, or higher production at the upper surface by light stress or aggregation. TEP concentrations did not present any significant cyclic diel pattern. Altogether, our results suggest that photobiological stress, sea ice melt and turbulence add to phytoplankton productivity in driving TEP distribution across the Antarctic Peninsula area and Atlantic sector of the Southern Ocean.
Paraules clau: Transparent exopolymer particles; Phytoplankton; Prokaryotes; Solar radiation dose; Southern Ocean