Articles

Els filtres actuals son: Any inici = 2020, Any final = 2021
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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.2020b)
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.