Research papers

The current filters are: Starting year = 2017, Ending year = 2018
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Olivar M.P., Contreras T., Hulley P.A., Emelianov M., López-Pérez C., Tuset V., Castellón A. (2018)
Progress in Oceanography, 160, 83-100. DOI: 10.1016/j.pocean.2017.12.005. (BibTeX: olivar.etal.2018)
Abstract: See
The vertical distributions of early developmental stages of oceanic fishes were investigated across the tropical and equatorial Atlantic, from oligotrophic waters close to the Brazilian coast to more productive waters close to the Mauritanian Upwelling Region. Stratification of the water column was observed throughout the study region. Fishes were caught with a MOCNESS-1 net with mouth area of 1m2 at 11 stations. Each station was sampled both during the day and at night within a single 24-h period. The investigation covered both larvae and transforming stages from the surface to 800m depth. Distribution patterns were analysed, and weighted mean depths for the larvae and transforming stages of each species were calculated for day and night conditions. Fortyseven different species were found. The highest number of species occurred in the three stations south of Cape Verde Islands, characterized by a mixture of South Atlantic Central Water (SACW) and Eastern North Atlantic Central Water (ENACW). There was a marked drop in species richness in the three stations closer to the African upwelling, dominated by ENACW. The highest abundances occurred in the families Myctophidae, Sternoptychidae, Gonostomatidae and Phosichthyidae. Day and night vertical distributions of larvae and transforming stages showed contrasting patterns, both in the depths of the main concentration layers in the water column, and in the diel migration patterns (where these were observed). Larvae generally showed a preference for the upper mixed layer (ca. 0–50 m) and upper thermocline (ca. 50–100 m), except for sternoptychids, which were also abundant in the lower thermocline layer (100–200 m) and even extended into the mesopelagic zone (down to 500 m). Transforming stages showed a more widespread distribution, with main concentrations in the mesopelagic zone (200–800 m). Larvae showed peak concentrations in the more illuminated and zooplankton-rich upper mixed layers during the day and a wider distribution through the upper 100m during the night. For most species, transforming stages were concentrated in the mesopelagic layers both day and night, although in some species (Diaphus cf. vanhoeffeni and Vinciguerria nimbaria), the transforming stages displayed vertical migration into the upper 100m at night, in a manner similar to their adult stages.
Keywords: Early life-history Ontogenetic vertical migration Mesopelagic fishes Lanternfishes Lightfishes Hatchetfishes
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Santis W., Aimola L., Campos E.J.D., Castellanos P. (2018)
Dynamics of Atmospheres and Oceans, 81, 30-41. DOI: 10.1016/j.dynatmoce.2017.11.004. (BibTeX: santis.etal.2018)
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The interdecadal variability of the atmospheric and oceanic meridional overturning circulation is studied, using a coupled model with two narrow meridional barriers representing the land and a flat bottomed Aquaplanet. Empirical orthogonal function (EOF) analysis are usedin the atmospheric and oceanic meridional overturning cells, revealing the atmospheric interdecadal variability is dominated by an annular mode, in both hemispheres, whichintroduces in the ocean a set of patterns of variability. The most energetic EOFs in the oceanare the barotropic responses from the annular mode. The interaction between the heat anomalies, due to the barotropic response, and the thermohaline circulation of each basinleads to a resonance mechanism that feeds back to the atmospheric forcing, modulatingthe annular mode spectrum. Besides the barotropic response, the annular mode introduces anomalies of salinity and temperature in the subtropical Atlantic that affects its upper buoy-ancy. These anomalies are incorporated within the ocean circulation and advected until theareas of deep sinking in the northern Atlantic, impacting on its overturning circulation as well
Keywords: AMOC Annular mode Idealized experiments
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Solé J., García-Olivares A., Turiel A., Ballabrera-Poy J. (2018)
Renewable Energy, 116, 258-271. DOI: 10.1016/j.renene.2017.09.035. (BibTeX: sole.etal.2018)
Abstract: See
We use the concept of Energy Return On energy Invested (EROI) to calculate the amount of the available net energy that can be reasonably expected from World oil liquids during the next decades (till 2040). Our results indicate a decline in the available oil liquids net energy from 2015 to 2040. Such net energy evaluation is used as a starting point to discuss the feasibility of a Renewable Transition (RT). To evaluate the maximum rate of Renewable Energy Sources (RES) development for the RT, we assume that, by 2040, the RES will achieve a power of 11 TW (1012 Watt). In this case, by 2040, between 10 and 20% of net energy from liquid hydrocarbons will be required. Taking into account the oil liquids net energy decay, we calculate the minimum annual rate of RES deployment to compensate it in different scenarios. Our study shows that if we aim at keeping an increase of 3% of net energy per annum, an 8% annual rate of RES deployment is required. Such results point out the urgent necessity of a determined policy at different levels (regional, national and international) favoring the RT implementation in the next decades
Keywords: EROI Energy transition Renewable energy Fossil fuels Oil liquids Net energy URR (Ultimate Recoverable Resources)
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Sturm U., Schade S., Ceccaroni L., Gold M., Kyba C.C.M., Claramunt B., Haklay M., Kasperowski D., Albert A., Piera J., Brier J., Kullenberg C., Luna S. (2018)
RIO Research Ideas and Outcomes, 4 DOI: 10.3897/rio.4.e23394. (BibTeX: sturm.etal.2018)
Abstract: See
Apps for mobile devices and web-based platforms are increasingly used in citizen science projects. While extensive research has been done in multiple areas of studies, from Human-Computer Interaction to public engagement in science, we are not aware of a collection of recommendations specific for citizen science that provides support and advice for planning, design and data management of mobile apps and platforms that will assist learning from best practice and successful implementations. In two workshops, citizen science practitioners with experience in mobile application and web-platform development and implementation came together to analyse, discuss and define recommendations for the initiators of technology based citizen science projects. Many of the recommendations produced during the two workshops are applicable to citizen science project that do not use mobile devices to collect data. Therefore, we propose to closely connect the results presented here with ECSA’s Ten Principles of Citizen Science.
Keywords: Citizen science, digital technologies, design, reuse, interoperability, sustainability
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Aparicio F.L., Nieto-Cid M., Calvo E., Pelejero C., López-Sanz A., Pascual J., Salat J., Sánchez-Pérez E.D., De La Fuente P., Gasol J.M., Marrasé C. (2017)
Science of The Total Environment, 609, 1001-1012. DOI: 10.1016/j.scitotenv.2017.07.170. (BibTeX: aparicio.etal.2017)
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Marine biogeochemistry dynamics in coastal marine areas is strongly influenced by episodic events such as rain, in- tense winds, river discharges and anthropogenic activities. We evaluated in this study the importance of these forc- ing events on modulating seasonal changes in the marine biogeochemistry of the northwestern coast of the Mediterranean Sea, based on data gathered from a fixed coastal sampling station in the area. A 4-year (2011– 2014) monthly sampling at four depths (0.5 m, 20 m, 50 m and 80 m) was performed to examine the time variability of several oceanographic variables: seawater temperature, salinity, inorganic nutrient concentrations (NO−3 , PO34− and SiO2), chlorophyll a (Chl a), dissolved organic carbon (DOC) and fluorescent dissolved organic matter (FDOM). FDOM dynamics was predominantly influenced by upwelling events and mixing processes, driven by strong and characteristic wind episodes. SW wind episodes favored the upwelling of deeper and denser waters into the shallower shelf, providing a surplus of autochthonous humic-like material and inorganic nutrients, whereas northerlies favored the homogenization of the whole shelf water column by cooling and evaporation. These different wind-induced processes (deep water intrusion or mixing), reported along the four sampled years, determined a high interannual environmental variability in comparison with other Mediterranean sampling sites.
Keywords: NW Mediterranean Wind events Salinity Inorganic nutrients DOC FDOM
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Barella-Ortiz A., Polcher J., de Rosnay P., Piles M., Gelati E. (2017)
Hydrology and Earth System Sciences, 21, 357-375. DOI: 10.5194/hess-21-357-2017. (BibTeX: barellaortiz.etal.2017a)
Abstract: See
L-band radiometry is considered to be one of the most suitable techniques to estimate surface soil moisture (SSM) by means of remote sensing. Brightness temperatures are key in this process, as they are the main input in the retrieval algorithm which yields SSM estimates. The work exposed compares brightness temperatures measured by the SMOS mission to two different sets of modelled ones, over the Iberian Peninsula from 2010 to 2012. The two modelled sets were estimated using a radiative transfer model and state variables from two land-surface models: (i) ORCHIDEE and (ii) H-TESSEL. The radiative transfer model used is the CMEM. Measured and modelled brightness temperatures show a good agreement in their temporal evolution, but their spatial structures are not consistent. An empirical orthogonal function analysis of the brightness temperature’s error identifies a dominant structure over the south-west of the Iberian Peninsula which evolves during the year and is maximum in autumn and winter. Hypotheses concerning forcing-induced biases and assumptions made in the radiative transfer model are analysed to explain this inconsistency, but no candidate is found to be responsible for the weak spatial correlations at the moment. Further hypotheses are proposed and will be explored in a forthcoming paper. The analysis of spatial inconsistencies between modelled and measured TBs is important, as these can affect the estimation of geophysical variables and TB assimilation in operational models, as well as result in misleading validation studies.
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Belmonte M., Stoffelen A., Verspeek J., Verhoef A., Neyt X., Anderson C. (2017)
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 10, 5, 2195 - 2204. DOI: https://doi.org/10.1109/JSTARS.2017.2647842. (BibTeX: belmonte.etal.2017)
Abstract: See
With an eye on the generation of a long-term climate record of ocean winds, soil moisture and sea ice extents across the C-band ERS and ASCAT scatterometer spans, a new calibration tool termed cone metrics has been developed. The new method is based on monitoring changes in the location and shape of the surface of maximum density of ocean backscatter measurements, also known as “the wind cone”. The cone metrics technique complements established calibration approaches, such as rain forest and NWP ocean calibration, through the characterization of linear as well as non-linear beam offsets, the latter via wind cone deformations. Given instrument evolution, proven stability and the monitoring by transponders, we take ASCAT-A data over 2013 as absolute calibration reference. This paper describes the new method and its application as inter- calibration tool in the context of the reprocessing activities for ERS-1 and ERS-2. Cone metrics succeeds at establishing the linear and non-linear corrections necessary to homogenize the ASCAT and ERS C-band records down to 0.05 dB.
Keywords: Radar signal processing, calibration, antenna radiation pattern.
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Casanova-Masjoan M., Pelegrí J.L., Sangrà P., Martínez A., Grisolía-Santos D., Pérez-Hernández M.D., Hernández-Guerra A. (2017)
Journal of Geophysical Research: Oceans, 122, 9, 7049-7065. DOI: 10.1002/2017JC012969. (BibTeX: casanovamasjoan.etal.2017)
Abstract: See
A South Atlantic ring is studied through remote sensing altimetry, hydrographic stations, and drifters’ trajectories. The ring’s core was characterized by warmer and saltier Indian Ocean waters. At the time of the cruise, the ring’s signature extended radially out to 124 km and vertically down to 2000 m, and its core absolute dynamic topography (ADT) exceeded the surrounding Atlantic Ocean waters in 0.4 m. The geo- strophic velocities were anticyclonic with maximum speeds about 35 cm s21 at 100 m and reaching negligible values near 4500 m. The rotational transport inside the ring was 33 Sv in the thermocline and intermediate layers. The drifters’ data distinguish a 30-km core revolving as a solid body with periodicity near 5 days and a transitional band that revolves with constant tangential velocity, resembling a Rankine vortex. The ADT data identify the ring’s track, showing that it was shed by the Agulhas Current retroflection in November 2009 and propagated northwest rapidly during the first 2 months (mean speed of about 10 cm s21) but slowed down substantially (3–4 cm s21) between March and July 2010, when it was last detected. The altimetry data also outlines the evolution of the ring’s core ADT, radius, vorticity, and, through a simple calibration with the cruise data, rotational transport. In particular, the ring surface and vertical-mean vorticity decay with time scales of 373 and 230 days, respectively, indicating that most of the property anomalies contained by the ring are dif- fused out to the subtropical gyre before it reaches the western boundary current system.
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Dall’Osto M., Ovadnevaite J., Paglione M., Beddows D.C.S., Ceburnis D., Cree C., Cortés P., Zamanillo M., Nunes S.O., Pérez G.L., Ortega-Retuerta E., Emelianov M., Vaqué D., Marrasé C., Estrada M., Sala M.M., Vidal M., Fitzsimons M.F., Beale R., Airs R., Rinaldi M., Decesari S., Facchini M.C., Harrison R.M., O’Dowd C., Simó R. (2017)
Scientific Reports, 7, 6047, 1-10. DOI: 10.1038/s41598-017-06188-x. (BibTeX: dallosto.etal.2017a)
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De La Fuente P., Pelegrí J.L., Canepa A., Gasser M., Domínguez F., Marrasé C. (2017)
Journal of Atmospheric and Oceanic Technology, 34, 2443-2455. DOI: 10.1175/JTECH-D-17-0090.1. (BibTeX: delafuente.etal.2017)
Abstract: See
The variability of a biogeochemical property in the ocean is the outcome of both nonconservative (such as respiration and photosynthesis) and conservative (mixing of water masses with distinct concentrations at origin) processes. Onemethod to separate both contributions is based on a multiple regression of the biogeochemical property in terms of temperature u and salinity S as conservative proxies of water masses. This regression delivers the variability related to the conservative fraction and hence allows for identifying the residual as the biogeochemical anomaly. Here, the standard multiple linear regression (MLR)method, which assumes that water masses mix locally and linearly, is compared with a nonlinear polynomial regression (PR) over the entire (u, S) space. The PR method has two important advantages overMLR: allows for simultaneous nonlinearmixing of all watermasses and does not require knowing the end-member water types. Both approaches are applied to data along 7.58N in the equatorial Atlantic Ocean, and the biogeochemical anomalies are calculated for humic-like fluorescent dissolved organic matter, apparent oxygen utilization, and nitrate—all of them related through in situ remineralization processes. The goodness of both approaches is assessed by analyzing the linear dependence and the coefficient of correlation between the anomalies. The results show that the PR method can be applied over the entire water column and yet retains the local variability associated with nonconservative processes. The potential of the PR approach is also illustrated by calculating the oxygen–nitrate stoichiometric ratio for the entire 7.58N transatlantic section.
Keywords: Atlantic Ocean; Water masses; Tracers
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Gabarro C., Turiel A., Elósegui P., Pla-Resina J., Portabella M. (2017)
The Cryosphere, 11, 1987-2002. DOI: 10.5194/tc-11-1987-2017. (BibTeX: gabarro.etal.2017)
Abstract: See
Monitoring sea ice concentration is required for operational and climate studies in the Arctic Sea. Technolo- gies used so far for estimating sea ice concentration have some limitations, for instance the impact of the atmosphere, the physical temperature of ice, and the presence of snow and melting. In the last years, L-band radiometry has been suc- cessfully used to study some properties of sea ice, remark- ably sea ice thickness. However, the potential of satellite L- band observations for obtaining sea ice concentration had not yet been explored. In this paper, we present preliminary evidence showing that data from the Soil Moisture Ocean Salinity (SMOS) mission can be used to estimate sea ice concentration. Our method, based on a maximum-likelihood estimator (MLE), exploits the marked difference in the radiative properties of sea ice and seawater. In addition, the brightness temperatures of 100 % sea ice and 100 % seawater, as well as their com- bined values (polarization and angular difference), have been shown to be very stable during winter and spring, so they are robust to variations in physical temperature and other geo- physical parameters. Therefore, we can use just two sets of tie points, one for summer and another for winter, for cal- culating sea ice concentration, leading to a more robust esti- mate. After analysing the full year 2014 in the entire Arctic, we have found that the sea ice concentration obtained with our method is well determined as compared to the Ocean and Sea Ice Satellite Application Facility (OSI SAF) dataset. How- ever, when thin sea ice is present (ice thickness 0.6 m), the method underestimates the actual sea ice concentration. Our results open the way for a systematic exploitation of SMOS data for monitoring sea ice concentration, at least for specific seasons. Additionally, SMOS data can be synergisti- cally combined with data from other sensors to monitor pan- Arctic sea ice conditions.
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García-Olivares A., Agüero A., Haupt B.J., Marcos M.J., Villar M.V., de Pablos J.L. (2017)
Science of The Total Environment, 593-594, 242-252. DOI: 10.1016/j.scitotenv.2017.03.152. (BibTeX: garciaolivares.etal.2017c)
Abstract: See
Worldwide tank spills represent 10% of the average annual input of oil in the sea. When such spills arise from wrecks at depth, neutralisation of environmental impacts is difficult to achieve. Extracting oil from sunken tankers is expensive, and, unfortunately, all of the oil cannot be extracted, as the Prestige case demonstrates. We propose an environmentally appropriate, cost-effective and proactive method to stop the long-term problem of leaks from sunken tankers similar to the Prestige. This method confines the wreck with a “sediment” capping of sepiolite mineral that emulates a natural sediment. A set of experiments and simulations shows that sepiolite has the characteristics necessary to accomplish the confinement of any current or future sunken tanker with minimal environmental perturbation.
Keywords: Oil spills, sunken tankers, environmental impact, confinement, sepiolite
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Gasser M., Pelegrí J.L., Emelianov M., Bruno M., Gràcia E., Pastor M., Peters H., Rodríguez-Santana A., Salvador J., Sánchez-Leal R.F. (2017)
Progress in Oceanography, 157, 47-71. DOI: 10.1016/j.pocean.2017.05.015. (BibTeX: gasser.etal.2017)
Abstract: See
The Mediterranean Water leaves the western end of the Strait of Gibraltar as a bottom wedge of salty and warm waters flowing down the continental slope. The salinity of the onset Mediterranean Outflow Water (MOW) is so high that leads to water much denser (initially in excess of 1.5 kg m 3) than the overlying central waters. During much of its initial descent, the MOW retains large salinity anomalies – causing density anomalies that induce its gravity current character – and relatively high westward speeds – caus- ing a substantial Coriolis force over long portions of its course. We use hydrographic data from six cruises (a total of 1176 stations) plus velocity data from two cruises, together with high-resolution bathymetric data, to track the preferential MOW pathways from the Strait of Gibraltar into the western Gulf of Cadiz and to examine the relation of these pathways to the bottom topography. A methodology for tributary systems in drainage basins, modified to account for the Coriolis force, emphasizes the good agreement between the observed trajectories and those expected from a topographically-constrained flow. Both contour avenues and cross-slope channels are important and have complementary roles steering the MOW along the upper and middle continental slope before discharging as a neutrally buoyant flow into the western Gulf of Cadiz. Our results show that the interaction between bottom flow and topography sets the path and final equilibrium depths of the modern MOW. Furthermore, they support the hypoth- esis that, as a result of the high erosive power of the bottom flow and changes in bottom-water speed, the MOW pathways and mixing rates have changed in the geological past.
Keywords: Mediterranean outflow water Strait of Gibraltar Gulf of Cadiz Topographic steering Bottom drainage system Along-slope contour avenues Down-slope erosional channels
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Isern-Fontanet J., Ballabrera-Poy J., Turiel A., García-Ladona E. (2017)
Nonlinear Processes in Geophysics, 24, 613-643. DOI: 10.5194/npg-24-613-2017. (BibTeX: isernfontanet.etal.2017)
Abstract: See
Ocean currents play a key role in Earth’s climate – they impact almost any process taking place in the ocean and are of major importance for navigation and human ac- tivities at sea. Nevertheless, their observation and forecasting are still difficult. First, no observing system is able to provide direct measurements of global ocean currents on synoptic scales. Consequently, it has been necessary to use sea surface height and sea surface temperature measurements and refer to dynamical frameworks to derive the velocity field. Second, the assimilation of the velocity field into numerical models of ocean circulation is difficult mainly due to lack of data. Recent experiments that assimilate coastal-based radar data have shown that ocean currents will contribute to increasing the forecast skill of surface currents, but require application in multidata assimilation approaches to better identify the thermohaline structure of the ocean. In this paper we review the current knowledge in these fields and provide a global and systematic view of the technologies to retrieve ocean ve- locities in the upper ocean and the available approaches to assimilate this information into ocean models.
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Jordà G., Von Schuckmann K., Josey S.A., Caniaux G., García-Lafuente J., Sammartino S., Özsoy E., Polcher J., Notarstefano G., Poulain P.M., Adloff F., Salat J., Naranjo C., Schroeder K., Chiggiato J., Sannino G., Macías D. (2017)
Progress in Oceanography, 156, 174-208. DOI: 10.1016/j.pocean.2017.07.001. (BibTeX: jorda.etal.2017)
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This paper presents a review of the state-of-the-art in understanding and quantification of the Mediterranean heat and mass (i.e. salt and water) budgets. The budgets are decomposed into a basin averaged surface component, lateral boundary components (through the Gibraltar and the Dardanelles Straits), a river input component and a content change component. An assessment of the different meth- ods and observational products that have been used to quantify each of these components is presented. The values for the long term average of each component are also updated based on existing literature and a first estimate of heat fluxes associated with the riverine input has been produced. Special emphasis is put on the characterization of associated uncertainties and proposals for advancing current knowledge are presented for each budget component. With the present knowledge of the different components, the Mediterranean budgets can be closed within the range of uncertainty. However, the uncertainty range remains relatively high for several terms, particularly the basin averaged surface heat fluxes. Consequently, the basin averaged heat budget remains more strongly constrained by the Strait of Gibraltar heat transport than by the surface heat flux. It is worth remarking that if a short ($few years) averaging period is used, then the heat content change must also be considered to constrain the heat budget. Concerning the water and salt fluxes, the highest uncertainties are found in the direct estimates of the Strait of Gibraltar water and salt transport. Therefore, the indirect estimate of those transports using the budget closure leads to smaller uncertain- ties than the estimates based on direct observations. Finally, estimates of Mediterranean heat and salt content trends are also reviewed. However, these cannot be improved through the indirect estimates due to the large temporal uncertainties associated to the surface fluxes and the fluxes through Gibraltar. The consequences of these results for estimates of the Mediterranean temperature and salinity trends obtained from numerical modelling are also considered.
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Lang S., Lin W. (2017)
Journal of Ocean Technology, 36, 1, 19-23. DOI: 10.3969/j.issn.1003-2029.2017.01.004. (BibTeX: lang.lin.2017)
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Lin W., Portabella M., Stoffelen A., Verhoef A. (2017)
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 10, 5, 2156-2164. DOI: 10.1109/JSTARS.2016.2616889. (BibTeX: lin.etal.2017)
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The sea-surface winds from the RapidScat scatterometer (RSCAT) onboard the International Space Station (ISS) have been produced using the Pencil-beam scatterometer Wind Processor (PenWP) since December 2014. An inversion residual or Maximum Likelihood Estimator (MLE-) based quality control (QC) algorithm is included in PenWP to distinguish between good- and poor-quality winds.Generally, the QC-accepted RSCAT winds are in good agreement with both the Advanced Scatterometer (ASCAT) winds and the European Centre for Medium-range Weather Forecasting (ECMWF) model output. In contrast, the QC-rejected winds present an overall positive bias with respect to ASCAT and ECMWF winds, mainly due to the impact of rain. However, it has been recently found that a considerable portion (>5%) of RSCAT QC-rejected contains anomalously low retrieved speeds (w< 4 m/s) under medium or high wind conditions (w > 10 m/s) according to ASCAT/ECMWF. This paper attempts to sort out the cause for these spuriously low winds. A revised MLE inversion with prefiltering the anomalous backscatters is proposed to correct the mentioned inversion issue. The impact of such improved inversion on the retrieved RSCAT winds is evaluated using both the collocated ASCAT and ECMWF winds.The results show that the proposed algorithm improves the wind retrieval of the spuriously low wind cases remarkably, while preserving about 4.7% of the nominal QC-rejected data (0.25% in total).
Keywords: Anomalous backscatter, low winds, quality control, rapidScat scatterometer, wind inversion.
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Lin W., Portabella M. (2017)
IEEE Transactions on Geoscience and Remote Sensing, 55, 7, 3922-3930. DOI: 10.1109/TGRS.2017.2683720. (BibTeX: lin.portabella.2017)
Abstract: See
Quality control (QC) is an essential part of the scatterometer wind retrieval. In the current pencil-beam scatterometer wind processor (PenWP), a maximum likelihood estimator (MLE)-based QC is used to discern between good- and poor-quality winds. MLE QC is generally effective in flagging rain contamination and increased subcell wind variability in the ocean surface wind vectors derived from Ku-band pencilbeam scatterometers, such as the RapidScat (RSCAT) installed on the International Space Station. However, the MLE is not an effective quality indicator over the outer swath where the inversion is underdetermined due to the lack of azimuthal diversity (including lack of horizontal polarized measurements). Besides, it is challenging to discriminate rain contamination from “true” high winds. This paper reviews several wind qualitysensitive indicators derived from the RSCAT data, such as MLE and its spatially averaged value (MLEm), and the singularity exponents (SE) derived from an image processing technique, called singularity analysis. Their sensitivities to data quality and rain are evaluated using collocated Advanced Scatterometer wind data, and global precipitation measurement satellite’s microwave imager rain data, respectively. It shows that MLEm and SE are the most effective indicators for filtering the poorest-quality winds over RSCAT inner and outer swath, respectively. A simple combination of SE and MLEm thresholds is proposed to optimize RSCAT wind QC. Comparing to the operational PenWP QC, the proposed method mitigates over-rejection at high winds, and improves the classification of good- and poor-quality winds.
Keywords: Quality control (QC), rain, scatterometer, singularity analysis (SA), winds.
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Liu L., Dong X., Lin W., Zhu J., Zhu D. (2017)
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 10, 5, 2372-2382. DOI: 10.1109/JSTARS.2016.2646840. (BibTeX: liu.etal.2017)
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Various reconstruction methods have been used to enhance the spatial resolution of scatterometer data. Most of the image reconstructions are two-dimensional problems, which combine multiple passes of overlapping data over the temporally homogeneous surface, and thus are only suitable for land and ice applications. This paper attempts to address the one-dimensional reconstruction to enhance the azimuth resolution of scatterometer data using a single pass of observations. Since the range resolution determined by the on-board dechirping technique is generally up to several hundred meters, the one-dimensional reconstruction is adequate for certain near real-time ocean applications, such as the development of coastal scatterometer winds. Three well-known reconstruction algorithms, including additive algebraic reconstruction technique (AART), multiplicative algebraic reconstruction technique (MART), and scatterometer image reconstruction (SIR), are evaluated. The spatial resolution and the reconstruction precision resolved by each algorithm are separately analyzed using the local impulse response andMonte Carlo methods. The dependence of the spatial resolution and the reconstruction precision on a variety of parameters, such as the mean backscatter coefficient and its variance, the beamwidth of spatial response function (SRF), and the SRF function type, is evaluated using a simulation framework. In particular, the tradeoff between the spatial resolution and the reconstruction precision is examined for three algorithms.The results show that SIR offers the quickest convergence and lowest noise.
Keywords: Local impulse response, reconstruction algorithms, resolution, scatterometer, spatial response function (SRF).
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Liu L., Dong X., Lin W., Zhu J., Zhu D. (2017)
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 10, 6, 2702-2712. DOI: 10.1109/JSTARS.2017.2679127. (BibTeX: liu.etal.2017a)
Abstract: See
A dual-frequency polarized scatterometer (DPSCAT) is proposed for the Chinese Water Cycle Observation Mission (WCOM) to be launched around 2020. DPSCAT is used to mea- sure the snow water equivalent (SWE) and the freeze/thaw state, which requires a measurement precision of 0.5 dB and a relatively higher spatial resolution (2–5 km) than the regular scatterometers (about 25 km). Therefore, the conventional range-gate dechirping along with the Doppler beam sharpening (DBS) technique is used by DPSCAT to achieve high range and azimuth resolution simul- taneously. However, DBS cannot improve the azimuth resolution over the nadir swath; thus, a new data processing, namely regu- larized deconvolution method (RDM), is explored to address this problem. In this paper, a quantitative analysis model is developed for RDM in order to study two crucial issues, i.e., the spatial res- olution (mainly for the nadir swath) and the accuracy/precision of the backscatter measurements after resolution enhancement. Nor- mally, the measurement precision and spatial resolution cannot be improved simultaneously using RDM. The accuracy/precision degrades as the spatial resolution improves, and vice versa. More- over, they both degrade as the measurement noise or uncertainty increases, which latter is usually defined as the normalized stan- dard deviation of the measurements (Kp ). In case of SWE retrieval that requires a reconstructed measurement precision of 0.5 dB, the best spatial resolution resolved by RDM is 3 km for Kp = 7%, 4kmforKp =10%,and5kmforKp =12%.
Keywords: Precision, regularized deconvolution method (RDM), resolution enhancement, scatterometer, spatial resolution.
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Mason E., Pascual A., Gaube P., Ruiz S., Pelegrí J.L., Delepoulle A. (2017)
Journal of Geophysical Research: Oceans, 122, 4, 3329-3357. DOI: 10.1002/2016JC012611. (BibTeX: mason.etal.2017)
Abstract: See
Horizontal and vertical motions associated with coherent mesoscale structures, including eddies and meanders, are responsible for significant global transports of many properties, including heat and mass. Mesoscale vertical fluxes also influence upper ocean biological productivity by mediating the supply of nutrients into the euphotic layer, with potential impacts on the global carbon cycle. The Brazil-Malvinas Confluence (BMC) is a western boundary current region in the South Atlantic with intense mesoscale activity. This region has an active role in the genesis and transformation of water masses and thus is a critical component of the Atlantic meridional overturning circulation. The collision between the Malvinas and Brazil Currents over the Patagonian shelf/slope creates an energetic front that translates offshore to form a vigorous eddy field. Recent improvements in gridded altimetric sea level anomaly fields allow us to track BMC mesoscale eddies with high spatial and temporal resolutions using an automated eddy tracker. We characterize the eddies across fourteen 5° × 5° subregions. Eddy-centric composites of tracers and geostrophic currents diagnosed from a global reanalysis of surface and in situ data reveal substantial subregional heterogeneity. The in situ data are also used to compute the evolving quasi-geostrophic vertical velocity (QG-ω) associated with each instantaneous eddy instance. The QG-ω eddy composites have the expected dipole patterns of alternating upwelling/downwelling, however, the magnitude and sign of azimuthally averaged vertical velocity varies among subregions. Maximum eddy values are found near fronts and sharp topographic gradients. In comparison with regional eddy composites, subregional composites provide refined information about mesoscale eddy heterogeneity.
Keywords: mesoscale eddies;vertical velocity;eddy compositing;subregional compositing;Brazil-Malvinas Confluence;quasi-geostrophic omega equation
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Olivar M.P., Hulley P.A., Castellón A., Emelianov M., López C., Tuset V.M., Contreras T., Molí B. (2017)
Progress in Oceanography, 151, 116–137. DOI: 10.1016/j.pocean.2016.12.001. (BibTeX: olivar.etal.2017a)
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In this investigation we analysed the changes in fish species occurrences and relative abundances across the tropical and equatorial Atlantic, and their vertical distribution patterns in relation to the different environmental scenarios. The study covers a wide region encompassing different water masses, and marked differences in productivity, from an oligotrophic zone close to the Brazilian coast, to a very productive upwelling region close to the Northwest African upwelling. Fishes were collected with a mediumsized midwater trawl (Mesopelagos), complemented by hauls made with a macrozooplankton net (MOCNESS). Species richness in the region was higher than in subtropical, temperate and cold regions. The total number of species and their overall abundance was lower in the stations closer to the Brazilian coast. Abundant species across the entire region were the gonostomatids Cyclothone alba, Cyclothone acclinidens, Cyclothone pallida and Cyclothone pseudopallida, the myctophid Lampanyctus alatus, the sternoptychid Sternoptyx diaphana, and the phosichthyid Vinciguerria nimbaria. The occurrences and abundances of C. parapallida, Lampanyctus nobilis and Lepidophanes guentheri were related to zones where AAIW waters occupied the mesopelagic layers, while other species such as Cyclothone livida and Polyipnus polli increased their abundance when AAIW disappears from their living depths. The presence of Eastern North Atlantic Central Water (ENACW) was associated with the occurrence of several myctophids (Benthosema glaciale, Ceratoscopelus maderensis, Diaphus holti, Diaphus rafinesquii, Hygophum hygomii, Lampanyctus crocodilus, Myctophum punctatum, Symbolophorus veranyi), and the gonostomatid Cyclothone braueri. In spite of the important differences in hydrographic features across the tropical and equatorial Atlantic, all stations showed either the general night migration into the epipelagic layers carried out by myctophids, phosicthyids, and some stomiids, or the presence of the several species of Cyclothone, sternoptychids and melamphaeids that remain in the mesopelagic layers, both day and night. The oxygen minimum zone (OMZ) at mesopelagic depths in the north-eastern sector does not seem to disrupt diel vertical migration. Day-night distributions in our study proved that mesopelagic migratory species are capable of crossing these wide hypoxic layers, and that some species such as Diaphus vanhoeffeni remain in these layers during the day. Other non-migratory fishes (Cyclothone spp. and S. diaphana) proved to be widely tolerant to these low oxygen concentrations, as shown by their high numerical abundances in the OMZ.
Keywords: Lanternfishes, lightfishes, hatchetfishes, diel migration, midwater trawls, diversity, zoogeography, water masses
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Olmedo E., Martínez J., Turiel A., Ballabrera-Poy J., Portabella M. (2017)
Remote Sensing of Environment, 193, 103–126. DOI: 10.1016/j.rse.2017.02.023. (BibTeX: olmedo.etal.2017b)
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The Soil Moisture and Ocean Salinity (SMOS) mission has provided a unique remote sensing capability for observing key variables of the hydrological cycle, such as the Sea Surface Salinity (SSS). However, due to some limitations related to the instrument interferometric concept and its challenging data processing, SMOS SSS maps still display significant artifacts and biases, especially close to the coast, mainly due to the presence of Radio Frequency Interferences (RFI) and Land-sea contamination (LSC). In this paper, a new methodology for filtering salinity retrievals and correcting for spatial biases is introduced and validated.
Keywords: Soil moisture and ocean salinity (SMOS) Sea Surface Salinity Salinity retrieval Remote sensing Physical oceanography
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Pérez-Hernández M.D., Hernández-Guerra A., Comas-Rodríguez I., Benítez-Barrios V.M., Fraile-Nuez E., Pelegrí J.L., Naveira-Garabato A.C. (2017)
Ocean Science, 13, 577–587. DOI: 10.5194/os-13-577-2017. (BibTeX: perezhernandez.etal.2017)
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Decadal differences in the Falkland Plateau are studied from the two full-depth hydrographic data collected during the ALBATROSS (April 1999) and MOC-Austral (February 2010) cruises. Differences in the upper 100 dbar are due to changes in the seasonal thermocline, as the ALBATROSS cruise took place in the austral fall and the MOCAustral cruise in summer. The intermediate water masses seem to be very sensitive to the wind conditions existing in their formation area, showing cooling and freshening for the decade as a consequence of a higher Antarctic Intermediate Water (AAIW) contribution and of a decrease in the Subantarctic Mode Water (SAMW) stratum. The deeper layers do not exhibit any significant change in the water mass properties. The Subantarctic Front (SAF) in 1999 is observed at 52.2–54.8º W with a relative mass transport of 32.6 Sv. In contrast, the SAF gets wider in 2010, stretching from 51.1 to 57.2º W (the Falkland Islands), and weakening to 17.9 Sv. Changes in the SAF can be linked with the westerly winds and mainly affect the northward flow of Subantarctic Surface Water (SASW), SAMW and AAIW/Antarctic Surface Water (AASW). The Polar Front (PF) carries 24.9 Sv in 1999 (49.8–44.4º W), while in 2010 (49.9–49.2º W) it narrows and strengthens to 37.3 Sv.
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Ramírez-Pérez M., Gonçalves-Araujo R., Wiegmann S., Torrecilla E., Bardají R., Röttgers R., Bracher A., Piera J. (2017)
Plos One. Open acces, 12, 1, 1-21. DOI: 10.137 1/journal .pone.017070 6. (BibTeX: ramirezperez.etal.2017b)
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The detection and prediction of changes in coastal ecosystems require a better understanding of the complex physical, chemical and biological interactions, which involves that observations should be performed continuously. For this reason, there is an increasing demand for small, simple and cost-effective in situ sensors to analyze complex coastal waters at a broad range of scales. In this context, this study seeks to explore the potential of beam attenuation spectra, c(λ), measured in situ with an advanced-technology optical transmissometer, for assessing temporal and spatial patterns in the complex estuarine waters of Alfacs Bay (NW Mediterranean) as a test site. In particular, the information contained in the spectral beam attenuation coefficient was assessed and linked with different biogeochemical variables. The attenuation at λ = 710 nm was used as a proxy for particle concentration, TSM, whereas a novel parameter was adopted as an optical indicator for chlorophyll a (Chl-a) concentration, based on the local maximum of c(λ) observed at the long-wavelength side of the red band Chl-a absorption peak. In addition, since coloured dissolved organic matter (CDOM) has an important influence on the beam attenuation spectral shape and complementary measurements of particle size distribution were available, the beam attenuation spectral slope was used to analyze the CDOM content. Results were successfully compared with optical and biogeochemical variables from laboratory analysis of collocated water samples, and statistically significant correlations were found between the attenuation proxies and the biogeochemical variables TSM, Chl-a and CDOM. This outcome depicted the potential of high-frequency beam attenuation measurements as a simple, continuous and cost-effective approach for rapid detection of changes and patterns in biogeochemical properties in complex coastal environments.
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Salat J., Lavín A., González-Pola C., Vélez-Belchí P., Sánchez R., Vargas-Yáñez M., García-Lafuente J., Marcos M., Gomis D. (2017)
CLIVAR Exchanges, 73, 32-38. (BibTeX: salat.etal.2017a)
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Sánchez E., Rodríguez B., Bladé I., Brunet M., Aznar R., Cacho I., Casado M.J., Gimeno L., Gutiérrez J.M., Jordá G., Lavín A., López J.A., Salat J., Valero B. (2017)
CLIVAR Exchanges, 73, 1-4. (BibTeX: sanchez.etal.2017b)
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Sánchez-Leal R.F., Bellanco M.J., Fernández-Salas L.M., García-Lafuente J., Gasser-Rubinat M., González-Pola C., Hernández-Molina F.J., Pelegrí J.L., Peliz A., Relvas P., Roque D., Ruiz-Villareal M., Sammartino S., Sánchez-Garrido J.C. (2017)
Science Advances, 3 DOI: 10.1126/sciadv.aao0609. (BibTeX: sanchezleal.etal.2017)
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The pathways and transformations of dense water overflows, which depend on small-scale interactions between flow dynamics and erosional-depositional processes, are a central piece in the ocean’s large-scale circulation. A novel, highresolution current and hydrographic data set highlights the intricate pathway travelled by the saline Mediterranean Overflow as it enters the Atlantic. Interaction with the topography constraints its spreading. Over the initial 200 km west of the Gibraltar gateway, distinct channels separate the initial gravity current into several plunging branches depth-sorted by density. Shallow branches follow the upper slope and eventually detach as buoyant plumes. Deeper branches occupy mid slope channels and coalesce upon reaching a diapiric ridge. A still deeper branch, guided by a lower channel wallmarked by transverse furrows, experiences small-scale overflows which travel downslope to settle at mid-depths. The Mediterranean salt flux into the Atlantic has implications for the buoyancy balance in the North Atlantic. Observations on how this flux enters at different depth levels are key to accurately measuring and understanding the role of Mediterranean Outflow in future climate scenarios.
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Stoffelen A., Aaboe S., Calvet J.C., Cotton J., De Chiara G., Figa J., Mouche A., Portabella M., Scipal K., Wagner W. (2017)
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 10, 5, 2086-2097. DOI: 10.1109/JSTARS.2017.2696424. (BibTeX: stoffelen.etal.2017)
Abstract: See
The second-generation exploitation of meteorological satellite polar system (EPS-SG) C-band-wavelength scatterometer instrument (called SCA), planned for launch in 2022, has a direct heritage from the successful advanced scatterometer (ASCAT) flown on the current EPS satellites. In addition, SCA will represent three major innovations with respect to ASCAT, namely: 1) Cross polarization and horizontal copolarization; 2) a nominal spatial resolution of 25 km; and 3) 20% greater spatial coverage than ASCAT. The associated expected science and application benefits that led the SCA design are discussed with respect to ocean, land, and sea ice applications for near-real time, climate monitoring, and research purposes. Moreover, an option to implement an ocean Doppler capability to retrieve the ocean motion vector is briefly discussed as well. In conclusion, the SCA instrument innovations are well set to provide timely benefits in all the main application areas of the scatterometer (winds, soil moisture, sea ice) and can be expected to contribute to new and more sophisticated meteorological, oceanographic, land, sea ice, and climate services in the forthcoming SCA era.
Keywords: Eddy currents, radar signal processing, sea ice, soil measurements, storms, wind.
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Vargas-Yáñez M., García-Martínez M.C., Moya F., Balbín R., López-Jurado J.L., Serra M., Zunino P., Pascual J., Salat J. (2017)
Progress in Oceanography, 157, 27-46. DOI: 10.1016/j.pocean.2017.09.004. (BibTeX: vargasyanez.etal.2017)
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The RADMED project is devoted to the implementation and maintenance of a multidisciplinary monitoring system around the Spanish Mediterranean waters. This observing system is based on periodic multidisciplinary cruises covering the coastal waters, continental shelf and slope waters and some deep stations (> 2000 m) from the Westernmost Alboran Sea to Barcelona in the Catalan Sea, including the Balearic Islands. This project was launched in 2007 unifying and extending some previous monitoring projects which had a more reduced geo- graphical coverage. Some of the time series currently available extend from 1992, while the more recent ones were initiated in 2007. The present work updates the available time series up to 2015 (included) and shows the capability of these time series for two main purposes: the calculation of mean values for the properties of main water masses around the Spanish Mediterranean, and the study of the interannual and decadal variability of such properties. The data set provided by the RADMED project has been merged with historical data from the MEDAR/MEDATLAS data base for the calculation of temperature and salinity trends from 1900 to 2015. The analysis of these time series shows that the intermediate and deep layers of the Western Mediterranean have increased their temperature and salinity with an acceleration of the warming and salting trends from 1943. Trends for the heat absorbed by the water column for the 1943–2015 period, range between 0.2 and 0.6 W/m2 depending on the used methodology. The temperature and salinity trends for the same period and for the in- termediate layer are 0.002 °C/yr and 0.001 yr−1 respectively. Deep layers warmed and increased their salinity at a rate of 0.004 °C/yr and 0.001 yr−1.
Keywords: Western Mediterranean Monitoring program Warming and salting trends Climate change
Viúdez A. (2017)
Journal of Fluid Mechanics, 824, R4, 1-12. DOI: 10.1017/jfm.2017.440. (BibTeX: viudez.2017)
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Long-term marginal stability of a new family of isolated oceanic vortices is analysed. Sign reversal of the radial gradient of the potential vorticity anomaly, as implied by the isolation requirement, leads to vortex unsteadiness but does not break the coherence of the vortex, which remains marginally stable even for high absolute Rossby numbers Ro approximate 0:8. The marginally stable vortices are characterized by a zero amount of potential vorticity anomaly on every isopycnal. The marginally stable final state is an unsteady vortex whose inner one-signed potential vorticity anomaly experiences revolution, rotation, precession and nutation.
Keywords: geophysical and geological flows, vortex flows, vortex instability
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Yu K., Dong C., King G. (2017)
Journal of Geophysical Research: Oceans, 122, 4 DOI: 10.1002/ 2016JC012404. (BibTeX: yu.etal.2017)
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We investigate mesoscale turbulence (10–1000 km) in the ocean winds over the Kuroshio Extension (28ºN–40ºN, 140ºE–180ºE) using the QuikSCAT data set (November 1999 to October 2009). We calculate the second (Djj) and third-order structure functions (Djjj) and the spatial variance (Vj) as a function of scale r (j5L; T denotes, respectively, the longitudinal (divergent) and transverse (vortical) component). The most interesting results of the analysis follow. Although both VjðrÞ and DjjðrÞ measure the turbulent kinetic energy (TKE), we find that VjðrÞ is the more robust measure. The spatial variance density (dVj/dr) has a broad peak near 450 km (close to the midlatitude Rossby radius of deformation). On interannual time scales, TKE correlates well with the El Ni~no 3.4 index. According to turbulence theory, the kinetic energy cascades downscale (upscale) if DLLLðrÞ (also skewness SL5DLLL=D3=2 LL ) is negative (positive). Our results for the Kuroshio Extension are consistent with a downscale cascade (indicating convergence dominates). Furthermore, classical turbulence theory predicts that SL520:3 and independent of r; however, we find SL varies strongly with r, from24 at small scales to 20.3 at large scales. This nonclassical behavior implies strong-scale interaction, which we attribute to the rapid, and sometimes explosive, growth of storms in the region through baroclinic instability. Finally, we find that ST (a measure of cyclonic/anticyclonic asymmetry) is positive (cyclonic) and also varies strongly with r, from 4 at small scales to 0.5 at large scales. New turbulence models are needed to explain these results, and that will benefit Weather Prediction and climate modeling.