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  • 1
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    Comparison of measured and modelled spectral UV irradiance at Izaña high mountain station: estimation of the underlying effective albedo (2015)
    Wiley
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    Publication Date: 2015-04-28
    Description: ABSTRACT In this work, we have carried out a comparison study between measured and modelled direct and global ultraviolet (UV) (300–400 nm) spectral irradiances and the determination of the surface effective albedo at the high altitude Izaña Observatory [IZO; 2400 m above sea level (a.s.l.)] located in Tenerife (Canary Islands, Spain). The spectral measurements were performed with a Bentham spectroradiometer during the Quality Assurance of Solar Ultraviolet Spectral Irradiance Measurements (QASUME) comparison campaign in June 2005. The simulations were obtained with the LibRadtran radiative transfer model. The model input parameters, such as total ozone and aerosol optical depth (AOD), were measured at IZO. The comparison between measured and modelled direct solar radiation component was made at 0.5 nm spectral resolution, showing excellent agreement, with differences below 5% for solar zenith angle (SZA) 〈 60°. These differences were attributed to the effect of the underlying surface albedo due to the frequent existence of a sea of clouds below the station altitude. The underlying surface albedo was determined using different methods. In spite of the variability of this parameter through the day due to the strong influence and variable structure of these underlying clouds, the mean of this effective surface albedo in the UV region gives a value between 0.2 and 0.5 in the UV range, 10 times higher than the local surface albedo (0.02–0.05).
    Print ISSN: 0899-8418
    Electronic ISSN: 1097-0088
    Topics: Geosciences , Physics
    Published by Wiley
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  • 2
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    Endorheic‐exorheic transitions of the Rio Grande and East African rifts (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract Tectonic extension of continental lithosphere creates accommodation space in which sediments are deposited. Climate‐driven processes provide the mechanism by which mass is detached from hillslopes and sediments are transported into this accommodation space. These two forcings, climate and tectonics, act together to create either endorheic (internally drained) or exorheic (externally drained) rift basins. Here we use a large‐scale dynamic landscape evolution‐tectonics model to understand the contribution of tectonic processes in endorheic‐exorheic transitions. In the model, extension results in opening of an asymmetric half‐graben along a listric normal fault. Rift opening occurs in the models in wet, temperate, or semi‐arid climates where runoff and evapotranspiration are varied. Our numerical experiments show that slow rift‐opening rates, a slowing‐down of rift opening, or increase of headwater topography (e.g., upstream epeirogenic uplift), are tectonic situations that can cause a transition from an endorheic to an exorheic drainage state in a rift basin. Our results also show that wet climate conditions lead to a permanent exorheism that persists regardless of rift opening rates. In semi‐arid climates, endorheic conditions are favored, and may last for the duration of rifting except for when rift opening is very slow. These results form an interpretive framework to study endorheic and exorheic drainage systems in natural continental rifts. In the slow‐opening Rio Grande rift, the endorheic‐exorheic transition may have occurred without dramatic climate changes. Lake‐level variations in East African rift basins are predicted by our models to result from variations in climate.
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
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    Performance evaluation of two high shear impellers in an unbaffled stirred tank (2015)
    Wiley
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    Publication Date: 2015-06-20
    Description: High shear impellers (HSIs) are mixers used in industrial stirred tanks to incorporate powders into liquid and break down particle agglomerates. In this work, a detail numerical study of two commercial ring-style HSIs of laboratory scale (Hockmeyer® Equipment Corp. D-Blade of two and four rings) was carried out at 50≤ Re ≤75, and their performance was compared with the Rushton Turbine (RT). It was found that power and pumping numbers or their ratio, cannot be simply connected for selecting properly an impeller in applications where highly localized viscous dissipation is desirable. The ratio of the average viscous dissipation in the impeller swept volume, , to the mean in the entire volume, , at two constant values of power input, P , was found to be lower for HSIs to that evaluated for RT. However, when P increases from 4.25 to 12.92 W , the dimensionless average viscous dissipation in the blade swept volume, at the higher P was found to be similar for the HSI of two rings and the RT, corroborating the high local viscous dissipation of this HSI when operated at higher speeds.
    Print ISSN: 0930-7516
    Electronic ISSN: 1521-4125
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 4
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    Solar radiation measurements compared to simulations at the BSRN Izaña station. Mineral dust radiative forcing and efficiency study (2013)
    Wiley
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    Publication Date: 2013-12-07
    Description: [1]  This paper presents a comparative study of shortwave downward radiation (SDR) measurements and simulations, obtained with the radiative transfer model (RTM) LibRadtran, at the Baseline Surface Radiation Network (BSRN) site of Izaña Atmospheric Observatory (IZA, Spain). The analysis is based on cloud-free days between March 2009 and August 2012 (386 days), including aerosol-free and Saharan mostly pure mineral dust conditions and comparing the day-to-day, annual and inter-annual variability.The observed agreement between simulations and measurements is excellent: the variance of daily measurements overall agrees within 99% with the variance of daily simulations and the mean bias (simulations - measurements) is -0.30 ± 0.24 MJm -2 (-1.1 ± 0.9%) for global, -0.16 ± 0.34 MJm -2 (-0.4 ± 0.9%) for direct and +0.02 ± 0.25 MJm -2 (+0.9 ± 9.2%) for diffuse SDR. Furthermore, the diurnally averaged aerosol radiative forcing ( Δ DF) and radiative forcing efficiency ( ΔDF eff ) due to Saharan mostly pure mineral dust events has been computed at Izaña Observatory. The mean Δ DF values are -7 ± 1, -96 ± 5 and 44 ± 2 Wm -2 for global, direct and diffuse BSRN SDR,respectively (mean aerosol optical depth, AOD, at 500 nm of 0.18 ± 0.01), while the mean ΔDF eff values are -59 ± 6, -495 ± 11 and 230 ± 8 Wm -2 per unit of AOD at 500 nm for global, direct and diffuse BSRN SDR, respectively. These values highlight the importance of scattering processes for mineral dust aerosols: the ratio between Δ DF and the corresponding SDR without aerosols is ~ 2.5% for diffuse SDR versus 0.2% for direct SDR. This illustrates the significant potential of mineral dust particles to cool the Earth-atmosphere system.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
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    Decoupled crust-mantle accommodation of Africa-Eurasia convergence in the NW Moroccan margin (2011)
    Wiley
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    Publication Date: 2011-08-16
    Description: The extent of the area accommodating convergence between the African and Iberian plates, how this convergence is partitioned between crust and mantle, and the role of the plate boundary in accommodating deformation are not well-understood subjects. We calculate the structure of the lithosphere derived from its density distribution along a profile running from the Tagus Abyssal Plain to the Sahara Platform and crossing the Gorringe Bank, the NW Moroccan margin, and the Atlas Mountains. The model is based on the integration of gravity, geoid, elevation, and heat flow data and on the crustal structure across the NW Moroccan margin derived from reflection and wide-angle seismic data. The resulting mantle density anomalies suggest important variations of the lithosphere-asthenosphere boundary (LAB) topography, indicating prominent lithospheric mantle thickening beneath the margin (LAB 〉 200 km depth) followed by thinning beneath the Atlas Mountains (LAB ∼90 km depth). At crustal levels the Iberia-Africa convergence is sparsely accommodated in a ∼950 km wide area and localized in the Atlas and Gorringe regions, with an inferred shortening of ∼50 km. In contrast, mantle thickening accommodates a 400 km wide region, thus advocating for a decoupled crustal-mantle mechanical response. A combination of mantle underthrusting due to oblique convergence, together with a viscous dripping fed by lateral mantle dragging, can explain the imaged lithospheric structure. The model is consistent with crustal shortening estimates and with the accommodation of part of the Iberia-Africa convergence farther NW of the Gorringe Bank and/or off the strike of the profile.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
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    CFD study of the flow induced by a grooved high-shear impeller in an unbaffled tank (2017)
    Wiley
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    Publication Date: 2017-12-16
    Description: A detailed hydrodynamic characterization in the transitional flow regime (20≤ Re ≤133) of two variants of the Norstone Polyblade® high-shear impeller (HSI), of industrial relevance, is presented. The study was carried out on a simulated Newtonian fluid using computational fluid dynamics (CFD). Measurements of power number were carried out in order to validate the simulation results. Hydrodynamic parameters considered of key importance in powder dispersion processes ( i.e. viscous dissipation and effective circulation), were used to assess the impellers’ performance. Furthermore, their performances were compared with reported data for two ring-style HSIs of two and four rings, and power number measurements of a sawtooth (Cowles type) impeller. The results show that both NR-type and Cowles impellers exhibit lower power number values, i.e. , they consume less power at a given Reynolds number than the two ring-style HSIs. In addition, it was found that at the same power input, the Norstone impellers induce higher maximum values of viscous dissipation than the two ring-style HSIs and suitable effective circulation, what in principle, makes them better suited for mixing dispersion processes.
    Print ISSN: 0930-7516
    Electronic ISSN: 1521-4125
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 7
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    Deep seated density anomalies across the Iberia‐Africa plate boundary and its topographic response (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract The modes in which the lithosphere deforms during continental collision and the mechanisms involved are not well understood. While continental subduction and mantle delamination are often invoked in tectonophysical studies, these processes are difficult to be confirmed in more complex tectonic regions such as the Gibraltar Arc. We study the present‐day density and compositional structure of the lithosphere along a transect running from S Iberia to N Africa crossing the western Gibraltar Arc. This region is located in the westernmost continental segment of the African‐Eurasian plates, characterized by a diffuse transpressive plate boundary. An integrated and self‐consistent geophysical‐petrological methodology is used to model the lithosphere structure variations and the thermophysical properties of the upper mantle. The crustal structure is mainly constrained by seismic experiments and geological data, whereas the composition of the lithospheric mantle is constrained by xenolith data. The results show large lateral variations in the topography of the lithosphere‐asthenosphere boundary (LAB). We distinguish different chemical lithospheric mantle domains that reproduce the main trends of the geophysical observables and the modelled P‐ and S‐wave seismic velocities. A sublithospheric body colder than the surrounding mantle is needed beneath the Betics‐Rif to adjust the measured potential fields. We link this body to the Iberian slab localized just to the east of the profile and having some effect on the geoid and Bouguer anomalies. Local isostasy allows explaining most of the topography, but an elastic thickness higher than 10 km is needed to explain local misfits between the Atlas and the Rif Mountains.
    Print ISSN: 2169-9313
    Electronic ISSN: 2169-9356
    Topics: Geosciences , Physics
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  • 8
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    A risk-based probabilistic framework to estimate the end-point of remediation: Concentration rebound by rate-limited mass transfer (2013)
    Wiley
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    Publication Date: 2013-03-05
    Description: Aquifer remediation is a challenging problem with environmental, social and economic implications. As a general rule, pumping proceeds until the concentration of the target substance within the pumped water lies below a pre-specified value. In this paper we estimate the a priori potential failure of the endpoint of remediation due to a rebound of concentrations driven by back diffusion. In many cases, it has been observed that once pumping ceases, a rebound in the concentration at the well takes place. For this reason, administrative approaches are rather conservative and pumping is forced to last much longer than initially expected. While a number of physical and chemical processes might account for the presence of rebounding, we focus here on diffusion from low water mobility into high mobility zones. In this work we look specifically at the concentration rebound when pumping is discontinued while accounting for multiple mass transfer processes occurring at different time scales and parametric uncertainty. We aim to a risk-based optimal operation methodology that is capable of estimating the endpoint of remediation based on aquifer parameters characterizing the heterogeneous medium as well as pumping rate and initial size of the polluted area.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
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  • 9
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    Reconciling modeled and observed temperature trends over Antarctica (2012)
    Wiley
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    Publication Date: 2012-08-28
    Description: Over the last three decades, ozone depletion over Antarctica has affected temperature and winds in the lower stratosphere, and even in the troposphere and at the surface. The second Chemistry Climate Model Validation activity (CCMVal2) concluded that chemistry-climate models simulate stratospheric cooling that is too large compared to observations, even though the modeled and observed ozone trends are similar. However, these comparisons were based only on radiosonde data available for 1969–1998. Here, we investigate trends in the Southern Hemisphere polar cap in the latest version of the Community Earth System Model (CESM1) with its high-top atmospheric component, WACCM4, fully coupled to an ocean model. We compare model trends with observations for different periods and with other modeling studies to show much better agreement with more recent data, and conclude that the discrepancy between observed trends and those calculated by high-top models may not be as large as previously reported.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 10
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    A new high‐resolution magnetic scanner for sedimentary sections (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract We developed a fully automated magnetic field scanner dedicated to uniaxial magnetic field measurements to determine remanent magnetization intensities and their variations in sedimentary U‐channels. A fluxgate magnetometer located as close as possible to the sedimentary section is used to perform uniaxial measurements of magnetic fields generated by the isothermal remanent magnetization of the sediment. This artificial magnetization, which is known to be a powerful proxy in environmental magnetism, is produced perpendicular to the U‐channel long axis, and parallel to the fluxgate axis, using a Halbach cylinder prior to the measurement. The present magnetic scanner offers a maximal spatial resolution of 5.8 mm for point sources. A spatial resolution of 14 mm is obtained for U channel samples. The magnetic scanner presents a reliable magnetic field range over about 3 orders of magnitude allowing measurement of magnetizations that saturate the Superconducting Rock Magnetometer in its classical configuration. The estimation of remanent magnetization intensities along the U‐channel is based on a modeling approach that uses successive uniformly magnetized prisms. In lacustrine laminated sections, comparison between modeling results based on prisms of a constant thickness, on prisms determined from sedimentary facies and on prisms determined from XRF (X‐Ray Fluorescence) data helps to understand the detrital vs. diagenetic history of the sedimentary succession.
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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