260 results on '"Emilio Cuevas"'
Search Results
102. Nonergodic Phases in Strongly Disordered Random Regular Graphs
- Author
-
Vladimir E. Kravtsov, Boris L. Altshuler, Lev Ioffe, Emilio Cuevas, Columbia University [New York], University of Murcia, Universidad de Murcia, Laboratoire de Physique Théorique et Modèles Statistiques (LPTMS), Centre National de la Recherche Scientifique (CNRS)-Université Paris-Sud - Paris 11 (UP11), L.D. Landau Institute for Theoretical Physics of RAS, Russian Academy of Sciences [Moscow] (RAS), and Abdus Salam International Centre for Theoretical Physics [Trieste] (ICTP)
- Subjects
Population ,Extrapolation ,General Physics and Astronomy ,FOS: Physical sciences ,01 natural sciences ,Condensed Matter::Disordered Systems and Neural Networks ,010305 fluids & plasmas ,Delocalized electron ,Singularity ,Quantum mechanics ,0103 physical sciences ,010306 general physics ,education ,Quantum ,Anderson impurity model ,Condensed Matter - Statistical Mechanics ,ComputingMilieux_MISCELLANEOUS ,Mathematical physics ,Physics ,[PHYS]Physics [physics] ,education.field_of_study ,Statistical Mechanics (cond-mat.stat-mech) ,Ergodicity ,Disordered Systems and Neural Networks (cond-mat.dis-nn) ,Condensed Matter - Disordered Systems and Neural Networks ,Exponent - Abstract
We combine numerical diagonalization with a semi-analytical calculations to prove the existence of the intermediate non-ergodic but delocalized phase in the Anderson model on disordered hierarchical lattices. We suggest a new generalized population dynamics that is able to detect the violation of ergodicity of the delocalized states within the Abou-Chakra, Anderson and Thouless recursive scheme. This result is supplemented by statistics of random wave functions extracted from exact diagonalization of the Anderson model on ensemble of disordered Random Regular Graphs (RRG) of N sites with the connectivity K=2. By extrapolation of the results of both approaches to N->infinity we obtain the fractal dimensions D_{1}(W) and D_{2}(W) as well as the population dynamic exponent D(W) with the accuracy sufficient to claim that they are non-trivial in the broad interval of disorder strength W_{E}10^{5} reveals a singularity in D_{1,2}(W)-dependencies which provides a clear evidence for the first order transition between the two delocalized phases on RRG at W_{E}\approx 10.0. We discuss the implications of these results for quantum and classical non-integrable and many-body systems., Comment: 4 pages paper with 5 figures + Supplementary Material with 5 figures
- Published
- 2016
103. Vertical mass impact and features of Saharan dust intrusions derived from ground-based remote sensing in synergy with airborne in-situ measurements
- Author
-
Emilio Cuevas, José Antonio Adame, Mar Sorribas, Mónica Navarro-Comas, Olga Puentedura, Javier Andrey-Andrés, Manuel Gil-Ojeda, Carmen Córdoba-Jabonero, and Laura Gómez
- Subjects
Atmospheric Science ,010504 meteorology & atmospheric sciences ,Spectrometer ,Dust ,010501 environmental sciences ,Mineral dust ,Atmospheric sciences ,01 natural sciences ,AERONET ,Aerosol ,Mass efficiency ,Troposphere ,LIDAR ,Lidar ,Environmental Science(all) ,Extinction (optical mineralogy) ,Mass concentration (chemistry) ,Environmental science ,Air quality impact ,Airborne measurements ,0105 earth and related environmental sciences ,General Environmental Science ,Remote sensing - Abstract
A study of the vertical mass impact of Saharan dust intrusions is presented in this work. Simultaneous ground-based remote-sensing and airborne in-situ measurements performed during the AMISOC-TNF campaign over the Tenerife area (Canary Islands) in summertime from 01 July to 11 August 2013 were used for that purpose. A particular dusty (DD) case, associated to a progressively arriving dust intrusion lasting for two days on 31 July (weak incidence) and 01 August (strong incidence), is especially investigated. AERONET AOD and AEx values were ranging, respectively, from 0.2 to 1.4 and 0.35 to 0.05 along these two days. Vertical particle size distributions within fine and coarse modes (0.16–2.8 μm range) were obtained from aircraft aerosol spectrometer measurements. Extinction profiles and Lidar Ratio (LR) values were derived from MPLNET/Micro Pulse Lidar observations. MAXDOAS measurements were also used to retrieve the height-resolved aerosol extinction for evaluation purposes in comparison to Lidar-derived profiles. The synergy between Lidar observations and airborne measurements is established in terms of the Mass Extinction Efficiency (MEE) to calculate the vertical mass concentration of Saharan dust particles. Both the optical and microphysical profilings show dust particles mostly confined in a layer of 4.3 km thickness from 1.7 to 6 km height. LR ranged between 50 and 55 sr, typical values for Saharan dust particles. In addition, this 2-day dust event mostly affected the Free Troposphere (FT), being less intense in the Boundary Layer (BL). In particular, rather high Total Mass Concentrations (TMC) were found on the stronger DD day (01 August 2013): 124, 70 and 21 μg m −3 were estimated, respectively, at FT and BL altitudes and on the near-surface level. This dust impact was enhanced due to the increase of large particles affecting the FT, but also the BL, likely due to their gravitational settling. However, the use of an assumed averaged MEE value can be especially critical for estimating the mass concentration of particular layers. Moreover, the potential of MAXDOAS retrieval for aerosol extinction profiling is also evidenced by showing a relatively good agreement with the Lidar-derived extinction profiles, once a particular smoothing procedure is applied to Lidar measurements.
- Published
- 2016
104. Saharan and arabian dust aerosols: a comparative case study of lidar ratio
- Author
-
Emilio Cuevas, Mar Sorribas, Carmen Córdoba-Jabonero, Ismail Sabbah, Faisal Al Sharifi, Manuel Gil-Ojeda, and José Antonio Adame
- Subjects
Lidar Ratio ,Aerosols ,010504 meteorology & atmospheric sciences ,Meteorology ,Dust particles ,Physics ,QC1-999 ,Extinction (astronomy) ,Dust storms ,Storm ,010501 environmental sciences ,Mineral dust ,Atmospheric sciences ,01 natural sciences ,Geography ,Lidar ,0105 earth and related environmental sciences - Abstract
El volumen 119 de 2016 de la revista EPJ Web of Conferences recoge las ponencias del 27th International Laser Radar Conference (ILRC 27) This work presents a first comparative study of the Lidar Ratio (LR) values obtained for dust particles in two singular dust-influenced regions: the Canary Islands (Spain, close to the African coast in the North Atlantic Ocean), frequently affected by Saharan dust intrusions, and the Kuwait area (Arabian Peninsula) as usually influenced by Arabian dust storms. Synergetic lidar and sun-photometry measurements are carried out in two stations located in these particular regions for that purpose. Several dusty cases were observed during 2014 in both stations and, just for illustration, two specific dusty case studies have been selected and analyzed to be shown in this work. In general, mean LR values of 54 sr and 40 sr were obtained in these studies cases for Saharan and Arabian dust particles, respectively. Indeed, these results are in agreement with other studies performed for dust particles arriving from similar desert areas. In particular, the disparity found in Saharan and Arabian dust LR values can be based on the singular composition of the suspended dust aerosols over each station. These results can be useful for CALIPSO extinction retrievals, where a single LR value (40 sr) is assumed for pure dust particles independently on the dust source region. This work has been supported by both the Spanish Ministerio de Economía y Competitividad (MINECO) under grant CGL2011-24891 (AMISOC project) and the Kuwait Foundation for the Advancement of Sciences under project 2011- 1401-01.
- Published
- 2016
105. Iodine monoxide in the north subtropical free troposphere
- Author
-
Manuel Gil, A. J. Gomez-Pelaez, T. D. Hay, Alfonso Saiz-Lopez, Emilio Cuevas, Olga Puentedura, J. Iglesias, Laura Gómez, and Mónica Navarro-Comas
- Subjects
Atmospheric Science ,010504 meteorology & atmospheric sciences ,Optical Absorption Spectroscopy ,Iodine monoxide ,02 engineering and technology ,Mineral dust ,Atmospheric sciences ,01 natural sciences ,Troposphere ,lcsh:Chemistry ,Monóxido de yodo ,Química estratosférica ,Observatory ,Mixing ratio ,Radiative transfer ,Zenith ,0105 earth and related environmental sciences ,Spectral signature ,Chemistry ,Differential optical absorption spectroscopy ,021001 nanoscience & nanotechnology ,lcsh:QC1-999 ,lcsh:QD1-999 ,13. Climate action ,0210 nano-technology ,lcsh:Physics - Abstract
Iodine monoxide (IO) differential slant column densities (DSCD) have been retrieved from a new multi-axis differential optical absorption spectroscopy (MAX-DOAS) instrument deployed at the Izaña subtropical observatory as part of the Network for the Detection of Atmospheric Composition Change (NDACC) programme. The station is located at 2370 m a.s.l., well above the trade wind inversion that limits the top of the marine boundary layer, and hence is representative of the free troposphere. We report daily observations from May to August 2010 at different viewing angles. During this period, the spectral signature of IO was unequivocally detected on every day of measurement. A mean IO DSCD of 1.52×1013 molecules cm−2 was observed at the 5° instrument elevation angle (IEA) on clear days using a single zenith reference for the reported period, with a day-to-day variability of 33% at one standard deviation. Based on the simulation of the DSCDs using radiative transfer calculations with five different hypothesized IO profiles, the IO mixing ratio is estimated to range between 0.2 and 0.4 pptv in the free troposphere. Episodes of Saharan dust outbreaks were also observed, with large increases in the DSCDs at higher IEA, suggesting an enhancement of IO inside the dust cloud.
- Published
- 2012
106. Assessment of global warming on the island of Tenerife, Canary Islands (Spain). Trends in minimum, maximum and mean temperatures since 1944
- Author
-
José Luis Martín, Emilio Cuevas-Agulló, and José Francisco Bethencourt
- Subjects
Atmospheric Science ,Global and Planetary Change ,Sea surface temperature ,Altitude ,Climatology ,Cloud cover ,Global warming ,Diurnal temperature variation ,Northern Hemisphere ,Environmental science ,Trade wind ,High mountain - Abstract
Temperature variation is studied at different altitudes and orientation on the island of Tenerife, according to the trends in the mean, maximum and minimum at 21 meteorological stations. Reference series are obtained by sectors, along with a representative overall series for Tenerife, in which temperature shows a statistically significant growth trend of 0.09 ± 0.04°C/decade since 1944. Night-time temperatures have risen most (0.17°C ± 0.04°C/decade), while by day they have been more stable. Consequently, the diurnal temperature range between day and night has narrowed. By regions, warming has been much more intense in the high mountains than the other sectors below the inversion layer between 600 and 1,400 m altitude, and progressively milder towards the coast. The temperature rise on the windward (north-northeast) slopes is greater than on the leeward side and could be related to the increase in cloudiness on the northern side. The general warming of the island is less than in continental areas at between 24 and 44oN, being closer to the sea surface temperature in the same area. This is probably explained largely by the insular conditions. In fact warming is more evident in the high mountains (0.14 ± 0.07°C/decade), where the tempering effect of the ocean and the impact of changes in the stratocumulus is weaker, being similar to the mean continental values in the northern hemisphere.
- Published
- 2012
107. Climatology of aerosol radiative properties in the free troposphere
- Author
-
Paolo Bonasoni, Emilio Cuevas, W. R. Leaitch, Daniel A. Jaffe, Ivo Kalapov, Elisabeth Andrews, J. Sun, Emily V. Fischer, Sangeeta Sharma, A. M. Macdonald, Patrick J. Sheridan, Paolo Laj, Neng Huei Lin, Angela Marinoni, John A. Ogren, Urs Baltensperger, Sergio Rodríguez, Todor Arsov, Ernest Weingartner, M. Collaud Coen, and Anne Jefferson
- Subjects
Atmospheric Science ,Angstrom exponent ,010504 meteorology & atmospheric sciences ,Backscatter ,Single-scattering albedo ,15. Life on land ,010501 environmental sciences ,Radiative forcing ,Atmospheric sciences ,01 natural sciences ,Aerosol ,Troposphere ,13. Climate action ,Extinction (optical mineralogy) ,Climatology ,Radiative transfer ,Environmental science ,0105 earth and related environmental sciences - Abstract
High altitude mountaintop observatories provide the opportunity to study aerosol properties in the free troposphere without the added expense and difficulty of making airborne measurements. Climatologies for free tropospheric aerosol radiative properties in cloud-free air, including light scattering, light absorption, light extinction, single scattering albedo, Angstrom exponent, hemispheric backscatter fraction and radiative forcing efficiency, from twelve high altitude (2.2–5.1 km) measurement platforms are presented at low relative humidity and at standard temperature and pressure. These climatologies utilize data from ten mountaintop observatories in the 20–50oN latitude band: Mauna Loa, USA; Lulin Mountain, Taiwan; Nepal Climate Observatory — Pyramid; Izana, Spain; Mount Waliguan, China; Beo Moussala, Bulgaria; Mount Bachelor, USA; Monte Cimone, Italy; Jungfraujoch, Switzerland; Whistler Mountain, Canada. Results are also included from two multi-year, in-situ aerosol vertical profiling programs: Southern Great Plains, USA and Bondville, USA. The amount of light absorption and scattering observed at these high altitude sites either peaks in the spring or it has a broad spring to summer enhancement. The seasonal variation of the aerosol single scattering albedo, backscatter fraction and Angstrom exponent changes from site to site but the timing can be related to aerosol sources and transport processes known to impact the individual sites. The seasonal variation of in-situ aerosol light extinction from these high altitude measurements is in excellent agreement with extinction values derived from CALIPSO lidar measurements. Analysis of the systematic variability among in-situ aerosol properties shows that these relationships can be used to infer aerosol types. In particular, the relationship between single scattering albedo and Angstrom exponent can indicate the presence of dust aerosol. Radiative forcing efficiency (RFE = aerosol forcing/aerosol optical depth) is used to assess the importance of single scattering albedo and backscatter fraction on aerosol forcing by eliminating aerosol amount (i.e., aerosol optical depth) from the calculation. Variability in monthly cycles of RFE corresponds with changes in single scattering albedo and hemispheric backscatter fraction. Utilizing site-specific, climatological values of single scattering albedo and backscatter fraction to calculate RFE results in departures from the monthly median values of RFE typically in the range 10–30%. The greatest discrepancy occurs for months with low aerosol loading where the observed variability of single scattering albedo and backscatter fraction is the greatest. At most sites the radiative forcing efficiency at low aerosol loading (light scattering −1 ) is slightly less negative (more warming) than at higher aerosol loading.
- Published
- 2011
108. Objective identification of synoptic meteorological patterns favouring African dust intrusions into the marine boundary layer of the subtropical eastern north Atlantic region
- Author
-
Emilio Cuevas, Silvia Alonso-Pérez, and Xavier Querol
- Subjects
Atmospheric Science ,geography ,Intrusion ,Marine boundary layer ,geography.geographical_feature_category ,Ridge ,Climatology ,Period (geology) ,Geopotential height ,Subtropics ,Mediterranean Basin ,Pressure level ,Geology - Abstract
Synoptic geopotential height anomalies patterns favouring African dust outbreaks into the marine boundary layer (MBL) of the subtropical Eastern North Atlantic Region (SENAR) were objectively identified. The proportion of the total variance explained by each of these patterns was also calculated. Dust intrusions into the MBL of the SENAR were identified using total suspended particles (TSP) data at a rural background station in Tenerife Island (El Rio station, ER). Geopotential height anomalies at 1,000, 850, 700 and 500 hPa, respectively, in days of African dust intrusion in the period 1998–2003 were grouped in monthly sets. Two different but complementary methods (K-means and Principal Components) were applied to daily geopotential height anomalies for each month and for each pressure level in case of African dust intrusion. Three principal geopotential height anomalies patterns were found. Type I consist on a high-pressure system over Europe that affects North Africa, occasionally giving rise to a ridge. The Canary Islands are in the south-west flank of this high-pressure system. This pattern is dominant throughout the whole year. Type II and type III patterns consist on a low located to the northeast and southeast of the Canary Islands, respectively, coupled with a high over the Mediterranean basin and/or North Africa. Two case analyses are presented, as well as a systematic validation of the meteorological pattern classification for all dust intrusions detected at ER station within the period 2004–2007.
- Published
- 2011
109. Trend changes of African airmass intrusions in the marine boundary layer over the subtropical Eastern North Atlantic region in winter
- Author
-
J. J. De Bustos, Xavier Querol, Silvia Alonso-Pérez, Roland R. Draxler, Carlos Pérez, Emilio Cuevas, and J. M. Baldasano
- Subjects
Atmospheric Science ,North Atlantic oscillation ,Anomaly (natural sciences) ,Climatology ,Trend surface analysis ,Geopotential height ,Environmental science ,Atmospheric model ,Subtropics ,Air mass ,Azores High - Abstract
African dust intrusions in the marine mixing layer of the Eastern North Atlantic subtropical region (23.5°N to 35°N) are favoured in winter when the eastern edge of the Azores High covers Southwestern Europe and North Africa. In situ ground pressure observations and reanalysis from National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) and European Centre for Medium-Range Weather Forecasts (ECMWF) indicate that the Azores High has strengthened and shifted eastward in winter over the last three decades. This is evidenced by the increase over time of the Madrid–Tenerife Index which is defined as the geopotential height anomaly difference at 1000 mb between Tenerife (28.5°N; 16.3°W) and Madrid (40.5°N; 3.5°W) in winter and of the African Index which is defined as the residence time over Africa of air mass trajectories entering the subtropical Eastern North Atlantic Ocean. Barcelona Supercomputing Center/Dust Regional Atmospheric Model (BSC-DREAM) dust regional model simulations from 1958 to 2006 were performed, assuming that the soil characteristics of dust sources remained unchanged over time. Simulated winter dust concentration levels are well correlated (0.67) with the available background observations for the 1998–2004 period. The model results show a two-fold increase in winter dust concentrations over the 1980–2006 period with respect to the 1958–1979 period, corresponding to the strengthening and eastward shift of the Azores High. DOI: 10.1111/j.1600-0889.2010.00524.x
- Published
- 2011
110. Fractal superconductivity near localization threshold
- Author
-
Lev Ioffe, Vladimir E. Kravtsov, Emilio Cuevas, Mikhail Feigel'man, L.D. Landau Institute for Theoretical Physics of RAS, Russian Academy of Sciences [Moscow] (RAS), Moscow Institute of Physics and Technology [Moscow] (MIPT), Laboratoire de Physique Théorique et Modèles Statistiques (LPTMS), Centre National de la Recherche Scientifique (CNRS)-Université Paris-Sud - Paris 11 (UP11), Department of Physics and Astronomy [Riverside], University of California [Riverside] (UCR), University of California-University of California, Abdus Salam International Centre for Theoretical Physics [Trieste] (ICTP), Izaña Atmospheric Research Center (IARC), and Agencia Estatal de Meteorología (AEMet)
- Subjects
Superconductivity ,Physics ,Local density of states ,Condensed matter physics ,Condensed Matter - Superconductivity ,Scanning tunneling spectroscopy ,Fermi level ,FOS: Physical sciences ,General Physics and Astronomy ,Fermi surface ,Fermi energy ,01 natural sciences ,010305 fluids & plasmas ,[PHYS.COND.CM-S]Physics [physics]/Condensed Matter [cond-mat]/Superconductivity [cond-mat.supr-con] ,Superconductivity (cond-mat.supr-con) ,symbols.namesake ,Condensed Matter::Superconductivity ,Pairing ,0103 physical sciences ,symbols ,010306 general physics ,Anderson impurity model - Abstract
We develop a semi-quantitative theory of electron pairing and resulting superconductivity in bulk "poor conductors" in which Fermi energy $E_F$ is located in the region of localized states not so far from the Anderson mobility edge $E_c$. We review the existing theories and experimental data and argue that a large class of disordered films is described by this model. Our theoretical analysis is based on the analytical treatment of pairing correlations, described in the basis of the exact single-particle eigenstates of the 3D Anderson model, which we combine with numerical data on eigenfunction correlations. Fractal nature of critical wavefunction's correlations is shown to be crucial for the physics of these systems. We identify three distinct phases: 'critical' superconductive state formed at $E_F=E_c$, superconducting state with a strong pseudogap, realized due to pairing of weakly localized electrons and insulating state realized at $E_F$ still deeper inside localized band. The 'critical' superconducting phase is characterized by the enhancement of the transition temperature with respect to BCS result, by the inhomogeneous spatial distribution of superconductive order parameter and local density of states. The major new feature of the pseudo-gaped state is the presence of two independent energy scales: superconducting gap $\Delta$, that is due to many-body correlations and a new "pseudogap" energy scale $\Delta_P$ which characterizes typical binding energy of localized electron pairs and leads to the insulating behavior of the resistivity as a function of temperature above superconductive $T_c$. Two gap nature of the "pseudo-gaped superconductor" is shown to lead to a number of unusual physical properties., Comment: 110 pages, 39 figures. The revised version corrects a number of typos, adds references and discussion of recent results
- Published
- 2010
111. The global SF6 source inferred from long-term high precision atmospheric measurements and its comparison with emission inventories
- Author
-
Emilio Cuevas, B. Neininger, Tobias Naegler, Ray L. Langenfelds, S. A. Zimov, J. Ilmberger, L. P. Steele, D. Osusko, Anja Engel, R. Weller, R. Heinz, Ingeborg Levin, Douglas E. J. Worthy, and C. v. Rohden
- Subjects
Atmospheric Science ,010504 meteorology & atmospheric sciences ,Climate change ,010501 environmental sciences ,7. Clean energy ,01 natural sciences ,Direct measure ,Term (time) ,Atmosphere ,Atmospheric measurements ,13. Climate action ,Climatology ,Greenhouse gas ,Environmental science ,Kyoto Protocol ,Sulphur Hexafluoride ,0105 earth and related environmental sciences - Abstract
Emissions of sulphur hexafluoride (SF6), one of the strongest greenhouse gases on a per molecule basis, are targeted to be collectively reduced under the Kyoto Protocol. Because of its long atmospheric lifetime (estimated as 800 to 3200 years), the accumulation of SF6 in the atmosphere is a direct measure of its global emissions. Examination of our extended data set of globally distributed high-precision SF6 observations shows an increase in SF6 abundance from near zero in the 1970s to a global mean of 6.7 ppt by the end of 2008. In-depth evaluation of our long-term data records shows that the global source of SF6 decreased after 1995, most likely due to SF6 emission reductions in industrialised countries, but increased again after 1998. By subtracting those emissions reported by Annex I countries to the United Nations Framework Convention of Climatic Change (UNFCCC) from our observation-inferred SF6 source leaves a surprisingly large gap of more than 70–80% of non-reported SF6 emissions in the last decade. This suggests a strong under-estimation of emissions in Annex I countries and underlines the urgent need for independent atmospheric verification of greenhouse gases emissions accounting.
- Published
- 2010
112. Origin and SEM analysis of aerosols in the high mountain of Tenerife (Canary Islands)
- Author
-
Francisco J. Expósito, Emilio Cuevas, Andrés Alastuey, Juan P. Díaz, A. M. Díaz, S. Castillo, Omaira García, Xavier Querol, and Juan D. Delgado
- Subjects
biology ,Meteorology ,National park ,Indoor bioaerosol ,biology.organism_classification ,Atmospheric sciences ,complex mixtures ,Aerosol ,Atmosphere ,Troposphere ,Diatom ,Quartz ,Geology ,Bioaerosol - Abstract
Focusing on aerosolized matter of relevance to respiratory health, a major public health issue worldwide, we studied mineral and biological aerosol (bioaerosol) composition (TSP and PM2.5) and geographical origins during dust intrusions in the Canary Islands. Seven days’ back- ward trajectories were assessed daily during March 2004 with the ends of back trajectories being the sampling station of Iza?a (high moun- tain, 2360 m a.s.l. at the Ca?adas del Teide National Park, Tenerife island), a free troposphere site allowing characterization of dust with low influence of other pollutant sources. Scanning electron microscopy (SEM) was used to survey major types of airborne particles in the dust plumes. Control, non-intrusion conditions correspond to Atlantic oceanic middle troposphere (OMT) air masses. Of the 14 samples taken, 1 corresponded to a control (clear atmosphere conditions), and the remaining 13 to dust intrusions, with the following sources: African Dust; EAM: mixture of Europe, Africa and Oceanic; MaA: maritime aerosols. Of the air masses, 79% were directly transported to the islands from Africa, and an increase of African dust events was detected when comparing with a 52-year previous data sequence. Quartz microcristals and aggregates of quartz and platy clay were the dominant minerals identified, with marine salt and gypsum also present. Freshwater diatom tests (from two Aulacoseira species) represented the most important biogenic aerosols, although fungi and pollen were also detected. The diverse and complex mixture of respirable particles in large quantities in airborne dust, especially from nearby Sahara and from the Sahelian region, is of maximum interest for air- way pathology in the Canaries, including the highly visited highlands in Tenerife.
- Published
- 2010
113. Aerosol characterization in Northern Africa, Northeastern Atlantic, Mediterranean Basin and Middle East from direct-sun AERONET observations
- Author
-
Carlos Pérez, Sara Basart, Gian Paolo Gobbi, Emilio Cuevas, and José María Baldasano
- Subjects
Mediterranean climate ,Atmospheric Science ,Angstrom exponent ,Climatology ,Environmental science ,Mineral dust ,Annual cycle ,Mediterranean Basin ,Aerosol ,Latitude ,AERONET - Abstract
We provide an atmospheric aerosol characterization for North Africa, Northeastern Atlantic, Mediterranean and Middle East based on the analysis of quality-assured direct-sun observations of 39 stations of the AErosol RObotic NETwork (AERONET) which include at least an annual cycle within the 1994–2007 period. We extensively test and apply the recently introduced graphical method of Gobbi and co-authors to track and discriminate different aerosol types and quantify the contribution of mineral dust. The method relies on the combined analysis of the Ångström exponent (α) and its spectral curvature δα. Plotting data in these coordinates allows to infer aerosol fine mode radius (Rf) and fractional contribution (η) to total Aerosol Optical Depth (AOD) and separate AOD growth due to fine-mode aerosol humidification and/or coagulation from AOD growth due to the increase in coarse particles or cloud contamination. Our results confirm the robustness of this graphical method. Large mineral dust is found to be the most important constituent in Northern Africa and Middle East. Under specific meteorological conditions, its transport to Southern Europe is observed from spring to autumn and decreasing with latitude. We observe "pure Saharan dust" conditions to show AOD>0.7 (ranging up to 5), α1.5 and δα~−0.2 corresponding to η>70% and Rf~0.13 μm. Here, dust mixed with fine pollution aerosols shifts the observations to the region α
- Published
- 2009
114. Prediction of the Composition of Fresh Pastures by Near Infrared Reflectance or Interactance-Reflectance Spectroscopy Predicción de la composición de pradera fresca mediante espectroscopía de reflectancia o interactancia-reflectancia en el infrarrojo cercano
- Author
-
Daniel Alomar, Rita Fuchslocher, José Cuevas, Rodrigo Mardones, and Emilio Cuevas
- Subjects
espectroscopía de reflectancia en infrarrojo cercano ,lcsh:GE1-350 ,predicción NIRS ,lcsh:S ,fibra óptica ,praderas frescas ,fresh pastures ,near infrared reflectance spectroscopy ,lcsh:Agriculture ,composición de praderas ,NIR prediction ,pasture composition ,lcsh:Environmental sciences ,fiber optics - Abstract
Fast and precise analytical tools can contribute to optimize pasture management decisions. This work was carried out to evaluate the potential of one such technique, near infrared spectroscopy (NIRS), to predict the nutritional value of pastures without previous drying of the samples, comparing two forms of collecting the spectra: reflectance, or interactance-reflectance (fiber optic probe). Samples (n = 107) from different swards were taken across the humid and temperate regions (Los Ríos and Los Lagos) of southern Chile. Once their spectra were collected, dry matter (DM) and several chemical constituents, such as crude protein (CP), metabolizable energy (ME), neutral (NDF) and acid detergent fiber (ADF), soluble carbohydrates (SC), soluble crude protein (SCP) and neutral detergent insoluble N (NDFIN), were determined as reference data. Calibrations were developed and the best ranked were selected (by cross-validation) according to a lower standard error of cross validation (SE CV) and a higher determination coefficient of cross validation (R²CV). Calibrations in the reflectance mode, for DM and CP, reached a high R²CV (0.99 and 0.91, respectively) and a SE CV (6.5 and 18.4 g kg-1). Equations for ADF, SCP and ME were ranked next, with R²CV of 0.87, 0.84 and 0.82, respectively, and SE CV of 15.88 g kg-1, 15.45 g kg-1 and 0.34 Mj kg-1. Equations for NDF, SC and NDFIN, with R²CV of 0.78, 0.77 and 0.61, respectively, and SE CV of 35.57, 94.54 and 1.89 g kg-1, respectively, are considered unreliable for prediction purposes. Interactance-reflectance, on the other hand, resulted in poorer equations for all fractions.Disponer de técnicas bromatológicas rápidas y precisas ayudaría a optimizar decisiones en el manejo de praderas. En este trabajo se evaluó el potencial de una de tales técnicas, la espectroscopía de reflectancia en el infrarrojo cercano (NIRS) para predecir el valor nutricional de praderas al estado fresco y comparar dos formas de colectar los espectros: reflectancia e interactancia-reflectancia (fibra óptica). Se colectaron 107 muestras de praderas en las regiones templado-húmedas del sur de Chile (Los Ríos y Los Lagos). Luego de tomar sus espectros, se analizaron por métodos de referencia para materia seca (DM), proteína bruta (CP), energía metabolizable (ME), fibra detergente neutro (NDF) y ácido (ADF), carbohidratos solubles (SC), proteína bruta soluble (SCP) y N insoluble en detergente neutro (NDFIN). Se desarrollaron calibraciones y se eligieron como mejores ecuaciones aquellas que en una validación cruzada, mostraron un mayor coeficiente de determinación (R²CV) y un menor error estándar (SE CV). Los mejores resultados se lograron en reflectancia para DM y CP, con R²CV de 0,99 y 0,91, respectivamente, y SE CV de 6,5 y 18,4 g kg-1, respectivamente. Luego se ubicaron las ecuaciones para ADF, SCP y ME, con valores R²CV de 0,87; 0,84 y 0,82 y SE CV de 15,88g kg-1, 15,45g kg-1 y 0,34 Mj kg-1, respectivamente. Las ecuaciones para NDF, SC y NDFIN, con R²CV de 0,78; 0,77 y 0,61 y SE CV de 35,57; 94,54 y 1,89 g kg-1, respectivamente; resultaron poco confiables para efectos de predicción. La técnica de interactancia-reflectancia produjo resultados inferiores para todas las fracciones.
- Published
- 2009
115. Comparison of ground-based Brewer and FTIR total column O3 monitoring techniques
- Author
-
Emilio Cuevas, C. Guirado, T. Blumenstock, Frank Hase, Alberto Redondas, and Matthias Schneider
- Subjects
Atmospheric Science ,Materials science ,Infrared ,Observatory ,Coincident ,Analytical chemistry ,Fourier transform infrared spectroscopy ,Column (database) - Abstract
We compare the currently most precise, ground-based total O3 measurement techniques: Brewer and FTIR. We give an overview of the similarities and the differences between the measurements and the retrieval approaches of both experiments. We compare coincident measurements performed at the Atmospheric Observatory of Izaña from 2005 to 2007 and demonstrate that, if the properties of the instruments are well characterised, the scatter between both experiments is as small as 0.5%. This is in agreement with the theoretical predictions and confirms empirically that both techniques are able to monitor total O3 amounts with a precision of better than 0.4%. However, we found systematic differences between both techniques of around 4.5%, which we think are mainly due to discrepancies between the applied UV and infrared spectroscopic parameters.
- Published
- 2008
116. Using 137Cs and 40K to identify natural Saharan dust contributions to PM10 concentrations and air quality impairment in the Canary Islands
- Author
-
Emilio Cuevas, Silvia Alonso-Pérez, M. López-Pérez, F. Hernandez, L. Karlsson, J. Hernández-Armas, and Sergio Rodríguez
- Subjects
Low altitude ,Atmospheric Science ,Meteorology ,Mineral dust ,Effects of high altitude on humans ,Atmospheric sciences ,Aerosol ,Ambient air ,Intrusion ,Environmental science ,media_common.cataloged_instance ,European union ,Air quality index ,General Environmental Science ,media_common - Abstract
Tenerife (Canary Islands) is often affected by Saharan mineral dust outbreaks. These events result in high PM10 concentrations in ambient air, well above the limiting values adopted by the European Union (Directive EU/1999/30). To comply with the EU Air Quality Directive, a quantitative proxy for the characterisation of high PM10 events is required. Furthermore, this proxy must be capable of differentiating natural sources (as defined by the Directive), such as Saharan mineral dust outbreaks, from other anthropogenic sources. In this study, we have analysed the time series of 137Cs, 40K and PM10 recorded at the island of Tenerife (2000–2006) in the Marine Boundary Layer (MBL), to test the possible usefulness of the two mentioned radiotracers as markers of Saharan mineral dust events. The results of the analysis showed that this is indeed the case for 137Cs and that there are, at least, two different sources of 40K concentrations in the collected atmospheric aerosol filters. While the detection of 137Cs in atmospheric aerosol filters could be directly associated with the arrival of low altitude ( 2000 m.a.s.l) dust intrusions. Moreover, two different mechanisms of aerosol loading in the MBL were, also, identified with the mentioned radiotracers. Good correlations (R2 > 0.6) were found between the three parameters when all the compiled data was considered. The correlation values increased to nearly 0.8 when only those samples that had 137Cs above detection limits were considered. The highest concentrations of 137Cs, 40K and PM10 were recorded in March 2004 in connection with a very intense low altitude Saharan dust intrusion. The results of this study, also, indicated that the 137Cs/40K ratio could be potentially useful to differentiate low from high altitude dust intrusions at this site.
- Published
- 2008
117. Influence of sea breeze circulation and road traffic emissions on the relationship between particle number, black carbon, PM1, PM2.5 and PM2.5–10 concentrations in a coastal city
- Author
-
Andrés Alastuey, Xavier Querol, Yenny González, Emilio Cuevas, P. M. Romero, Noemí Pérez, Ramón Ramos, and Sergio Rodríguez
- Subjects
Pollutant ,Atmospheric Science ,Meteorology ,Particle number ,Air pollution ,Particulates ,medicine.disease_cause ,Atmospheric sciences ,Aerosol ,Sea breeze ,Ultrafine particle ,medicine ,Environmental science ,Daylight ,General Environmental Science - Abstract
The physical characterisation of metrics representative of ambient air particle concentration is becoming a topic of great interest for urban air quality monitoring and human exposure assessment. In this article, the influence of sea breeze circulation and primary road traffic emissions on the relationship between the urban aerosol number (N3, particles >3 nm), black carbon
- Published
- 2008
118. Trace element variation in size-fractionated African desert dusts
- Author
-
S. Castillo, Teresa Moreno, Xavier Querol, Emilio Cuevas, Mohammed Mounkaila, Andrés Alastuey, Ludger Herrmann, and Wes Gibbons
- Subjects
Ecology ,Continental crust ,Trace element ,Mineralogy ,Fractionation ,Inductively coupled plasma ,Particulates ,Calcareous ,Inductively coupled plasma mass spectrometry ,Ecology, Evolution, Behavior and Systematics ,Geology ,Earth-Surface Processes ,Zircon - Abstract
Desert particulate samples from locations in the Sahara–Sahel dust corridor (Western Sahara, Algeria, Chad and Niger) were segregated into size fractions ranging from 20 μm and analysed using inductively coupled plasma atomic emission spectrometry (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS). The size-fractionated samples contain higher concentrations of Al, Na, Mg, Fe and most trace elements in the finer, phyllosilicate-rich materials. A notable exception is provided by Zr and Hf, which concentrate in the coarser fractions due to a higher abundance of coarse detrital zircon. Equally explicable by natural processes are enrichments (relative to the average upper continental crust) in incompatible trace elements with higher ionic potential (Nb, Ce, La), these being more resistant to chemical weathering. In contrast, samples show a relative loss of large ion lithophile elements (Rb, Cs and Ba), and the more calcareous samples show relative enrichment in Sr and depletion in Nb. However, not all the geochemical variations exhibited by these samples are easily explicable by invoking “natural” geochemical processes: anomalous concentrations of several transition metals (Zn, Pb, Cd) can be attributed to anthropogenic pollution, and enrichments in Cr, Ni and Mo are due to abrasive interaction between the siliceous dust sample and the fractionation equipment.
- Published
- 2008
119. Origin of observed high 7Be and mineral dust concentrations in ambient air on the Island of Tenerife
- Author
-
M. López-Pérez, J. Hernández-Armas, Silvia Alonso-Pérez, F. Hernandez, Sergio Rodríguez, L. Karlsson, and Emilio Cuevas
- Subjects
Atmosphere ,Atmospheric Science ,Meteorology ,Ultrafine particle ,Environmental science ,Atmospheric model ,Mineral dust ,Particulates ,Atmospheric sciences ,Scavenging ,Air mass ,General Environmental Science ,Aerosol - Abstract
Temporal series of atmospheric PM 1 and PM 10 matter (particulate matter with aerodynamic diameter below 1 and 10 μm) as well as 40 K and 7 Be concentrations in aerosol filters, collected in the Island of Tenerife from 30 June 2003 until 17 January 2005, were analysed here to: (1) study the variability of 7 Be in the atmosphere at this site and (2) to identify the origin of high 7 Be events and check their possible connection with the transport of Saharan dust to Tenerife. A complex relationship was observed between PM 10 matter and 7 Be concentrations in the measured aerosol filters. Due to this fact, the analysed atmospheric events had to be grouped in: (I) high 7 Be and high PM 10 matter events; (II) low 7 Be and high PM 10 matter events; and (III) high 7 Be and low PM 10 matter events. The low 7 Be and low PM 10 matter events were not considered in this study. The results indicated that four times during the study period significant concentrations of 7 Be were observed with the arrival of suspended material from the African continent. An enhanced scavenging effect of the 7 Be available in the aerosol transport zone by the re-suspended material is believed to have caused these detected increments in local atmospheric concentrations. Seventy-two hours forecasts created with the Dust Regional Atmospheric model (DREAM model) for these events, also, seem to support this hypothesis.
- Published
- 2008
120. High resolution modelling results of the wind flow over Canary Islands during the meteorological situation of the extratropical storm Delta (28–30 November 2005)
- Author
-
Carlos Marrero, Emilio Cuevas, Oriol Jorba, and José María Baldasano
- Subjects
Delta ,Atmospheric Science ,geography ,Atlantic hurricane ,geography.geographical_feature_category ,Ecological Modeling ,Subtropical cyclone ,Mesoscale meteorology ,Storm ,lcsh:QC851-999 ,Atmospheric sciences ,Pollution ,lcsh:QC1-999 ,Wind speed ,Geophysics ,Climatology ,Archipelago ,Extratropical cyclone ,Environmental science ,lcsh:Q ,lcsh:Meteorology. Climatology ,lcsh:Science ,lcsh:Physics - Abstract
On 28–29 November 2005 an extratropical storm affected the Canary Islands causing significant damage related to high average wind speeds and intense gusts over some islands of the archipelago. Delta was the twenty-sixth tropical or subtropical storm of the 2005 Atlantic hurricane season. It represents an unusual meteorological phenomenon for that region, and its impacts were underestimated by the different operational meteorological forecasts during the previous days of the arrival of the low near Canary Islands. The aim of this study is to reproduce the local effects of the flow that were observed over the Canary Islands during the travel of the Delta storm near the region using high-resolution mesoscale meteorological simulations. The Advanced Research Weather Research & Forecasting Model (WRF-ARW) is applied at 9, 3 and 1 km horizontal resolution using ECMWF forecasts as initial and boundary conditions. The high-resolution simulation will outline the main features that contributed to the high wind speeds observed in the archipelago. Variations in vertical static stability, vertical windshear and the intense synoptic winds of the southwestern part of Delta with a warm core at 850 hPa were the main characteristics that contributed to the development and amplification of intense gravity waves while the large-scale flow interacted with the complex topography of the islands.
- Published
- 2008
121. NO2 climatology in the northern subtropical region: diurnal, seasonal and interannual variability
- Author
-
Manuel Gil, Andreas Richter, Martyn P. Chipperfield, Margarita Yela, Olga Puentedura, J. Iglesias, L. N. Gunn, Emilio Cuevas, S. Rodríguez, Monica Navarro, and I. Alonso
- Subjects
Atmospheric Science ,Chemical transport model ,Diurnal cycle ,Climatology ,Sunrise ,Satellite ,Sunset ,Atmospheric sciences ,Annual cycle ,Zenith ,SCIAMACHY - Abstract
Daily NO2 vertical column density (VCD) has been routinely measured by zenith sky spectroscopy at the subtropical station of Izaña (28° N, 16° W) since 1993 in the framework of the Network for the Detection of Atmospheric Composition Change (NDACC). Based on 14 years of data the first low latitude NO2 VCD climatology has been established and the main characteristics from short timescales of one day to interannual variability are presented. Instrumental descriptions and different sources of errors are described in detail. The observed diurnal cycle follows that expected by gas-phase NOx chemistry, as can be shown by the good agreement with a vertically integrated chemical box model, and is modulated by solar radiation. The seasonal evolution departs from the phase of the hours of daylight, indicating the signature of upper stratospheric temperature changes. From the data record (1993–2006) no significant long-term trends in NO2 VCD can be inferred. Comparison of the ground-based data sets with nadir-viewing satellite spectrometers shows excellent agreement for SCIAMACHY with differences between both datasets of 1.1%. GOME displays unrealistic features with the largest discrepancies during summer. The ground-based data are compared with long-term output of the SLIMCAT 3-D chemical transport model (CTM). The basic model, forced by ECMWF (ERA-40) analyses, captures the observed NO2 annual cycle but significantly underestimates the spring/summer maximum (by 12% at sunset and up to 25% at sunrise). In a model run which uses assimilation of satellite CH4 profiles to constrain the model long-lived tracers the agreement is significantly improved. This improvement in modelled column NO2 is due to better modelled NOy profiles and points to transport errors in the ECMWF ERA-40 reanalyses.
- Published
- 2008
122. The contributions of 'minimum primary emissions' and 'new particle formation enhancements' to the particle number concentration in urban air
- Author
-
Sergio Rodríguez and Emilio Cuevas
- Subjects
Fluid Flow and Transfer Processes ,Atmospheric Science ,Environmental Engineering ,Meteorology ,Particle number ,Chemistry ,Mechanical Engineering ,Air pollution ,Exhaust gas ,Atmospheric sciences ,medicine.disease_cause ,Pollution ,Dilution ,Aerosol ,Atmosphere ,Ultrafine particle ,medicine ,Particle - Abstract
In an urban site affected by fresh vehicle exhaust emissions, the ambient air number concentrations of particles coarser than 3 nm (N) was split into two components, N = N 1 + N 2 . This was done using a method based on the high correlation between black-carbon (BC) and number (N) concentrations which is typically observed in ambient air and is the result of vehicle exhaust emissions. The component N1 accounts for “those aerosol components directly emitted in the particle phase” and “those components nucleating immediately after emission”. The component N2 accounts for the new particle formation enhancements during the “dilution and cooling of the vehicle exhaust” and is also influenced by “in situ new particle formation in ambient air”. The contribution of N1 to N exhibits a maximum of 55% during the morning rush hours (07:00–08:00). The contribution of N2 to N exhibits a daily evolution with a broad maximum during daylight (as solar radiation intensity), while for about 7 h (11:00–17:00) the N2 contribution to N is about 70%. During some “afternoon N2 events”, N2 contributions exceeded 90%. Enhancements in the new particle formation processes may increase the N/BC concentrations ratio in one order of magnitude, from 4.82 × 10 6 particles/ng BC to 47 × 10 6 particles/ng BC and during some events up to 97 × 10 6 particles/ng BC. The results show evidence of the high potential of the vehicle exhausts and of the urban atmosphere to trigger new particle formation if the ambient air conditions are favourable. The method used in this study is useful in assessing future changes in the number to BC relationship due to forthcoming regulations in the vehicle exhaust emissions.
- Published
- 2007
123. Chemical composition and complex refractive index of Saharan Mineral Dust at Izaña, Tenerife (Spain) derived by electron microscopy
- Author
-
Peter Knippertz, Emilio Cuevas, Ulrich Bundke, Stephan Weinbruch, Lothar Schütz, Martin Ebert, Nathalie Benker, Konrad Kandler, and Sergio Rodríguez
- Subjects
Atmospheric Science ,Materials science ,Mineralogy ,Hematite ,Mineral dust ,medicine.disease_cause ,complex mixtures ,Soot ,Aerosol ,visual_art ,Particle-size distribution ,medicine ,visual_art.visual_art_medium ,Particle size ,Quartz ,Chemical composition ,General Environmental Science - Abstract
Samples from two strong homogeneous dust plumes from the Saharan desert reaching Izana (Tenerife, Spain) in July and August 2005 were taken with a miniature impactor system and filter samplers. Size, aspect ratio and chemical composition of more than 22,000 individual particles were studied by scanning electron microscopy. The mineralogical phase composition of about 200 particles was investigated by transmission electron microscopy. In addition, the aerosol size distribution was measured with an optical particle spectrometer. In all samples, the aerosol was dominated by mineral dust with an average composition (by volume) of 64% silicates, 6% quartz, 5% calcium-rich particles, 14% sulfates, 1% hematite, 1% soot and 9% other carbonaceous material. Sulfate was found predominantly as coating on other particles with an average thickness of approximately 60 nm. The aerosol calcium content is correlated with the calcite concentrations of soils in the source region, highest values were observed for northern and central Algeria and Morocco. The average aspect ratio of the particles was 1.64. The distributions of the aspect ratios are parameterized by log-normal functions for modeling purpose. Single-scattering albedo (0.95) and asymmetry factor (0.74–0.81) was measured by polar aerosol photometry on filter samples using a light source resembling the solar spectrum. The apparent soot content of the sample (1 vol%) was determined by the same technique. From the mineralogical data, an average complex refractive index of 1.59–9×10 −3 i for visible light was derived. The imaginary part of the complex refractive index decreases with increasing particle size from −2.5×10 −2 i to −3 i, reflecting the decreasing hematite and soot contents. The imaginary part derived from optical measurements was −7×10 −3 i.
- Published
- 2007
124. Impact of the Saharan dust outbreaks on the ambient levels of total suspended particles (TSP) in the marine boundary layer (MBL) of the Subtropical Eastern North Atlantic Ocean
- Author
-
Xavier Querol, Silvia Alonso-Pérez, J. C. Guerra, Emilio Cuevas, and Mar Viana
- Subjects
Troposphere ,Atmospheric Science ,Deposition (aerosol physics) ,Climatology ,Outbreak ,Environmental science ,Subtropics ,Mineral dust ,Particulates ,Atmospheric sciences ,Air mass ,General Environmental Science ,Aerosol - Abstract
Six years (1998–2003) of measurements of ambient air concentrations of total suspended particulate (TSP) measured at a rural background monitoring station in Tenerife (Canary Islands), the El Rio station (ER, 28°08′35″N, 16°39′20″W, 500 m a.s.l.) were studied. African dust outbreaks were objectively identified using a new quantitative tool, called the African Index. This index indicates the percentage of time that an air mass remained over an African region at one of three possible height intervals of the lower troposphere. After identifying these episodes, a study of the background TSP levels at the ER station and of direct and indirect (those which cause vertical deposition of dust) African air mass intrusion impacts was performed. Taking into account both direct and indirect episodes, a total of 322 days of African dust intrusion were objectively identified (a mean of 54 episodes per year) in the period 1998–2003, some of them caused by “transition episodes” or “return African air masses”. A subjective method confirmed that 256 of these days were caused by direct impacts of African dust on the ER station. A mean TSP value of 21.6 μg m−3 was found at the station during this period. All the episodes occurred when the TSP concentration was >28.5 μg m−3. The TSP background (∼14 μg m−3) can be assumed to be representative of the MBL of the Eastern North Atlantic subtropical region. The highest number of dust gravitational settlement (or indirect) episodes occurs in summer, but the highest contribution of these episodes to the TSP levels is in March with a monthly mean TSP contribution of up to 30.5 μg m−3.
- Published
- 2007
125. UV Index Experimental Values During the Years 2000 and 2001 from the Spanish Broadband UV-B Radiometric Network¶
- Author
-
R. Vergaz, Emilio Cuevas, José A. Martínez-Lozano, Victoria E. Cachorro, José Manuel Vilaplana, Jerónimo Lorente, Benito de la Morena, Carlos González-Frías, María P. Utrillas, Alberto Redondas, Francisco J. Expósito, Juan P. Díaz, M. J. Marín, Xavier de Cabo, Luis Sánchez-Muniosguren, F. Tena, and Ángel M. de Frutos
- Subjects
Pyranometer ,Meteorology ,Cloud cover ,Irradiance ,General Medicine ,Noon ,Atmospheric sciences ,medicine.disease_cause ,Biochemistry ,Spectroradiometer ,Ozone layer ,medicine ,Environmental science ,Ultraviolet index ,Physical and Theoretical Chemistry ,Ultraviolet - Abstract
An analysis is made of experimental ultraviolet erythemal solar radiation data measured during the years 2000 and 2001 by the Spanish UV-B radiation evaluation and prediction network. This network consists of 16 Robertson-Berger type pyranometers for evaluating solar erythemal radiation and five Brewer spectroradiometers for evaluating the stratospheric ozone. On the basis of these data the Ultraviolet Index (UVI) was evaluated for the measuring stations that are located either in coastal regions or in the more densely populated regions inland on the Iberian Peninsula. It has been checked that in most cases the maximum irradiance values corresponded to solar noon, although there were exceptions that could be explained by cloudiness. The maximum experimental values of the UVI were around 9 during the summer, though frequently passing this value at the inland measurement stations. The annual accumulated dose of irradiation on a horizontal plane has also been studied, as well as the evolution through the year in units of energy, standard erythemal doses and minimum erythemal doses, according to different phototypes.
- Published
- 2007
126. Origin of the exceedances of the European daily PM limit value in regional background areas of Spain
- Author
-
Emilio Cuevas, Xavier Querol, Anna Avila, and Miguel Escudero
- Subjects
Pollutant ,Atmospheric Science ,Meteorology ,Advection ,Diurnal temperature variation ,Air pollution ,Seasonality ,Atmospheric sciences ,medicine.disease ,medicine.disease_cause ,Aerosol ,medicine ,Environmental science ,Air quality index ,Air mass ,General Environmental Science - Abstract
The origin of the daily exceedances of 50 μg PM10 m−3 (daily limit value or DLV of the EU air quality directive) and of an arbitrary daily value (DV) 35 μg PM2.5 m−3 recorded in 2001–2003 in 13 regional background stations of the Iberian Peninsula were interpreted. This was carried out by means of back-trajectory analysis, available PM model outputs, satellite data and meteorological maps. This allows the detection of high PM episodes on a regional scale and the study of their seasonal and geographical variability. The number of exceedances of the PM10 DLV ranged in 2001–2003 from 6 to 41 depending on the monitoring site. For the selected PM2.5 DV, the range of daily exceedances was 0–10 in the study period. The majority of the PM10 (>70% in most stations) and PM2.5 (17–55% in most stations) exceedances in regional background monitoring stations are caused by African dust outbreaks. These exceedances were less frequent in winter than in summer due to: (a) the frequent long range transport of dust in the warm seasons over Iberia, (b) the re-suspension associated with convective atmospheric dynamics, and (c) the relative low rainfall favouring re-suspension and high residence time of PM. Moreover, a regional contribution of secondary aerosols derived from the efficient photochemical transformation of gaseous precursors may coincide with African transport in summer. Episodes with lack of advective conditions caused 2–29% and 20–50% of the PM10 and PM2.5 exceedances. These occurred mainly in summer due to poor renovation of air masses, increased convective re-suspension, dispersion of pollutants towards rural areas and regional re-circulation and aging of air masses which result in the proliferation of secondary inorganic species. Long-range transport of PM from continental Europe caused exceedances (9–40% and 18–38% of the PM10 and PM2.5 exceedances, respectively), only in northern Iberia because, as the European air masses evolve towards the south, the pollutants suffer dispersion/dilution. Local exceedances are associated with the advection of the clean Atlantic air masses, which cannot increase PM levels to a great extent without the influence of a local source of PM. The proportion of local exceedances of PM10 and PM2.5 ranged 6–33% and 17–40%, respectively.
- Published
- 2007
127. Bloch states in light transport through a perforated metal
- Author
-
Vladimir Gasparian, Zh. S. Gevorkian, and Emilio Cuevas
- Subjects
Physics ,Diffraction ,Condensed matter physics ,Condensed Matter - Mesoscale and Nanoscale Physics ,Plane (geometry) ,Surface plasmon ,General Physics and Astronomy ,FOS: Physical sciences ,Physics::Optics ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Transverse plane ,Wavelength ,Perforated metal ,0103 physical sciences ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,Transmission coefficient ,010306 general physics ,0210 nano-technology ,Quantum tunnelling ,Optics (physics.optics) ,Physics - Optics - Abstract
Light transport in a metal with two-dimensional hole arrays is considered. Analytical expression for a transmission coefficient in periodic, isolated and disordered cases are derived, assuming the existence of waveguide modes transverse tunneling in two-dimensional plane perpendicular to traveling direction of light. The one dimensional case of periodic holes, due to its simplicity, is investigated in detail. In the dilute metal regime, when metal fraction is small, our numerical study of the transmission coefficient of central diffracted wave indicates the existence of a minimum which is completely independent of an incident wavelength. Further increasing of metal fraction leads to the unusual monotonic increasing of central diffracted wave transmission. The role of the surface plasmons is discussed., 14pages, 2figures
- Published
- 2015
128. Validation of reactive gases and aerosols in the MACC global analysis and forecast system
- Author
-
Henk Eskes, Michael Schulz, Natalia Sudarchikova, Stefan Kinne, A. Wagner, Simon Chabrillat, Jan Griesfeller, M. Razinger, J. Kapsomenakis, Mihalis Vrekoussis, Valérie Thouret, Antti Arola, Andreas Richter, Bavo Langerock, Richard Engelen, Vincent Huijnen, Martin G. Schultz, Idir Bouarar, Olivier Boucher, E. Botek, Anna Benedictow, L. Jones, Anne-Marlene Blechschmidt, Eleni Katragkou, Christos Zerefos, Audrey Gaudel, Emilio Cuevas, Harald Flentje, Royal Netherlands Meteorological Institute (KNMI), Finnish Meteorological Institute (FMI), Norwegian Meteorological Institute [Oslo] (MET), Universität Bremen, Belgian Institute for Space Aeronomy / Institut d'Aéronomie Spatiale de Belgique (BIRA-IASB), Laboratoire de Météorologie Dynamique (UMR 8539) (LMD), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-École des Ponts ParisTech (ENPC)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Max Planck Institute for Meteorology (MPI-M), Max-Planck-Gesellschaft, Izaña Atmospheric Research Center (IARC), Agencia Estatal de Meteorología (AEMet), European Centre for Medium-Range Weather Forecasts (ECMWF), Meteorologisches Observatorium Hohenpeißenberg (MOHp), Deutscher Wetterdienst [Offenbach] (DWD), Laboratoire d'aérologie (LAERO), Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Academy of Athens, Aristotle University of Thessaloniki, Forschungszentrum Jülich GmbH | Centre de recherche de Juliers, Helmholtz-Gemeinschaft = Helmholtz Association, Cyprus Institute (CyI), Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-École des Ponts ParisTech (ENPC)-École polytechnique (X)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC), Centre National de la Recherche Scientifique (CNRS)-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), and Université Fédérale Toulouse Midi-Pyrénées
- Subjects
Aerosols ,Service (systems architecture) ,Earth observation ,010504 meteorology & atmospheric sciences ,Meteorology ,lcsh:QE1-996.5 ,Scoring methods ,010501 environmental sciences ,Remote sensing ,[SDU.STU.ME]Sciences of the Universe [physics]/Earth Sciences/Meteorology ,01 natural sciences ,Atmospheric composition ,lcsh:Geology ,Data assimilation ,13. Climate action ,Component (UML) ,Greenhouse gas ,Aerosoles ,Teledetección ,Environmental science ,Air quality index ,ddc:910 ,0105 earth and related environmental sciences - Abstract
The European MACC (Monitoring Atmospheric Composition and Climate) project is preparing the operational Copernicus Atmosphere Monitoring Service (CAMS), one of the services of the European Copernicus Programme on Earth observation and environmental services. MACC uses data assimilation to combine in situ and remote sensing observations with global and regional models of atmospheric reactive gases, aerosols, and greenhouse gases, and is based on the Integrated Forecasting System of the European Centre for Medium-Range Weather Forecasts (ECMWF). The global component of the MACC service has a dedicated validation activity to document the quality of the atmospheric composition products. In this paper we discuss the approach to validation that has been developed over the past 3 years. Topics discussed are the validation requirements, the operational aspects, the measurement data sets used, the structure of the validation reports, the models and assimilation systems validated, the procedure to introduce new upgrades, and the scoring methods. One specific target of the MACC system concerns forecasting special events with high-pollution concentrations. Such events receive extra attention in the validation process. Finally, a summary is provided of the results from the validation of the latest set of daily global analysis and forecast products from the MACC system reported in November 2014.
- Published
- 2015
129. Numerical Modelling of the Extratropical Storm Delta Over Canary Islands: Importance of High Resolution
- Author
-
Carlos Marrero, Emilio Cuevas, José María Baldasano, and Oriol Jorba
- Subjects
Delta ,Altitude ,Geography ,Climatology ,Wind shear ,Extratropical cyclone ,Maximum sustained wind ,Storm ,Tropical cyclone ,Atmospheric sciences ,Wind speed - Abstract
The tropical storm “Delta” was formed on November 23, 2005 in a sea zone of the subtropical Atlantic south of the Azores. After days with an erratic movement, the day 27 the storm reinforced their intensity and accelerated its movement towards the Northeast in the direction of the Canary Islands. On 28 and 29, it made a transition to extratropical storm, affecting the Canary Islands with very strong sustained winds with maximum streak of 152 km/h at the airport of La Palma and close to 250 km/h in the Izana observatory (2,360 m altitude), which caused significant property damage. The aim of this numerical modelling is to reproduce the local effects of Delta storm with high spatial resolution. The WRF-ARW model is applied from 9 to 3 km of horizontal resolution using ECMWF forecasts as IBC. The simulation reproduces the main features that contributed to the high wind speeds observed. Variations in the vertical static stability, vertical wind shear and intense synoptic winds from the southwest part of Delta with a warm core at 850 hPa were the main features that have contributed to the development and amplification of intense gravitational waves, while the large-scale flow interacted with the complex topography of the islands. Nonhydrostatic and hydrostatic experiments were designed taking into account the settings and domain factors. The results associated with changes relative to a controlled simulation showed that the boundary layer, the horizontal resolution, and the nonhydrostatic option have the greatest impact.
- Published
- 2015
130. A random matrix model with localization and ergodic transitions
- Author
-
Emilio Cuevas, M. Amini, Ivan M. Khaymovich, Vladimir E. Kravtsov, Department of Applied Physics, Aalto-yliopisto, and Aalto University
- Subjects
Physics ,Anderson localization ,Spectrum (functional analysis) ,General Physics and Astronomy ,FOS: Physical sciences ,Function (mathematics) ,Multifractal system ,Disordered Systems and Neural Networks (cond-mat.dis-nn) ,Eigenfunction ,Condensed Matter - Disordered Systems and Neural Networks ,16. Peace & justice ,Correlation function ,Ergodic theory ,Statistical physics ,Random matrix - Abstract
Motivated by the problem of Many-Body Localization and the recent numerical results for the level and eigenfunction statistics on the random regular graphs, a generalization of the Rosenzweig-Porter random matrix model is suggested that possesses two localization transitions as the parameter $\gamma$ of the model varies from 0 to $\infty$. One of them is the Anderson transition from the localized to the extended states that happens at $\gamma=2$. The other one at $\gamma=1$ is the transition from the extended non-ergodic (multifractal) states to the extended ergodic states similar to the eigenstates of the Gaussian Orthogonal Ensemble. We computed the two-level spectral correlation function, the spectrum of multifractality $f(\alpha)$ and the wave function overlap which all show the transitions at $\gamma=1$ and $\gamma=2$., Comment: 8 pages, 9 figures (main text) + 7 pages, 4 figures (supplementary materials)
- Published
- 2015
131. Modulation of Saharan dust export by the North African dipole
- Author
-
Javier López-Solano, Joseph M. Prospero, Emilio Cuevas, Andrés Alastuey, Xavier Querol, Sergio Rodríguez, Silvia Alonso-Pérez, and M. I. García
- Subjects
Variabilidad climática ,Atmospheric Science ,Meteorología ,Geopotential height ,Tropics ,Subtropics ,Distribución de partículas de polvo ,Mineral dust ,Monsoon ,Convergence zone ,Atmospheric sciences ,Rainband ,lcsh:QC1-999 ,lcsh:Chemistry ,lcsh:QD1-999 ,Anticyclone ,Climatology ,Meteorología - Sahara ,Distribution of dust ,Environmental science ,Climate variability ,lcsh:Physics ,Sahara - Abstract
We have studied the relationship between the long-term interannual variability in large-scale meteorology in western North Africa – the largest and most active dust source worldwide – and Saharan dust export in summer, when enhanced dust mobilization in the hyper-arid Sahara results in maximum dust impacts throughout the North Atlantic. We address this issue by analyzing 28 years (1987–2014) of summer averaged dust concentrations at the high-altitude Izaña observatory (~ 2400 m a.s.l.) on Tenerife, and satellite and meteorological reanalysis data. The summer meteorological scenario in North Africa (aloft 850 hPa) is characterized by a high over the the subtropical Sahara and a low over the tropics linked to the monsoon. We measured the variability of this high–low dipole-like pattern in terms of the North African dipole intensity (NAFDI): the difference of geopotential height anomalies averaged over the subtropics (30–32° N, Morocco) and the tropics (10–13° N, Bamako region) close to the Atlantic coast (at 5–8° W). We focused on the 700 hPa standard level due to dust export off the coast of North Africa tending to occur between 1 and 5 km a.s.l. Variability in the NAFDI is associated with displacements of the North African anticyclone over the Sahara and this has implications for wind and dust export. The correlations we found between the 1987–2014 summer mean of NAFDI with dust at Izaña, satellite dust observations and meteorological re-analysis data indicate that increases in the NAFDI (i) result in higher wind speeds at the north of the Inter-Tropical Convergence Zone that are associated with enhanced dust export over the subtropical North Atlantic, (ii) influence the long-term variability of the size distribution of exported dust particles (increasing the load of coarse dust) and (iii) are associated with enhanced rains in the tropical and northern shifts of the tropical rain band that may affect the southern Sahel. Interannual variability in NAFDI is also connected to spatial distribution of dust over the North Atlantic; high NAFDI summers are associated with major dust export (linked to winds) in the subtropics and minor dust loads in the tropics (linked to higher rainfall), and vice versa. The evolution of the summer NAFDI values since 1950 to the present day shows connections to climatic variability (through the Sahelian drought, ENSO (El Niño–Southern Oscillation) and winds) that have implications for dust export paths. Efforts to anticipate how dust export may evolve in future decades will require a better understanding of how the large-scale meteorological systems represented by the NAFD will evolve. The Izaña GAW program is funded by AEMET and by the Minister of Economy and Competitiveness of Spain (POLLINDUST, CGL2011-26259) J. M. Prospero’s research is supported by NSF grant AGS-0962256 5.114 JCR (2015) Q1, 6/84 Meteorology and atmospheric sciences UEC
- Published
- 2015
132. Geochemical variations in aeolian mineral particles from the Sahara–Sahel Dust Corridor
- Author
-
Teresa Moreno, Emilio Cuevas, S. Castillo, Mohammed Mounkaila, Xavier Querol, Josep Elvira, Andrés Alastuey, Ludger Herrmann, Wes Gibbons, Moreno, Teresa, Querol, Xavier, Alastuey, Andrés, Moreno, Teresa [0000-0003-3235-1027], Querol, Xavier [0000-0002-6549-9899], and Alastuey, Andrés [0000-0002-5453-5495]
- Subjects
Geologic Sediments ,Environmental Engineering ,Evaporite ,Health, Toxicology and Mutagenesis ,Geochemistry ,Mineralogy ,Weathering ,Wind ,Phosphates ,chemistry.chemical_compound ,Sahara-Sahel Dust ,Africa, Northern ,Environmental Chemistry ,Aerosols ,Air Pollutants ,Minerals ,Mineral aerosols ,biology ,Harmattan ,Public Health, Environmental and Occupational Health ,Dust ,Dust and soil geochemistry ,General Medicine ,General Chemistry ,biology.organism_classification ,Pollution ,chemistry ,Clastic rock ,Aeolian processes ,Carbonate ,Sedimentary rock ,Lile ,Environmental Monitoring - Abstract
The Sahara-Sahel Dust Corridor runs from Chad to Mauritania and expels huge amounts of mineral aerosols into the Atlantic Ocean. Data on samples collected from Algeria, Chad, Niger, and Western Sahara illustrate how corridor dust mineralogy and chemistry relate to geological source and weathering/transport history. Dusts sourced directly from igneous and metamorphic massifs are geochemically immature, retaining soluble cations (e.g., K, Na, Rb, Sr) and accessory minerals containing HFSE (e.g., Zr, Hf, U, Th) and REE. In contrast, silicate dust chemistry in desert basins (e.g., Bodélé Depression) is influenced by a longer history of transport, physical winnowing (e.g., loss of Zr, Hf, Th), chemical leaching (e.g., loss of Na, K, Rb), and mixing with intrabasinal materials such as diatoms and evaporitic salts. Mineral aerosols blown along the corridor by the winter Harmattan winds mix these basinal and basement materials. Dusts blown into the corridor from sub-Saharan Africa during the summer monsoon source from deeply chemically weathered terrains and are therefore likely to be more kaolinitic and stripped of mobile elements (e.g., Na, K, Mg, Ca, LILE), but retain immobile and resistant elements (e.g., Zr, Hf, REE). Finally, dusts blown southwestwards into the corridor from along the Atlantic Coastal Basin will be enriched in carbonate from Mesozoic-Cenozoic marine limestones, depleted in Th, Nb, and Ta, and locally contaminated by uranium-bearing phosphate deposits. © 2006 Elsevier Ltd. All rights reserved., We thank Dr. Jenny Pike (Cardiff University, UK) for help with diatom identification. This study was supported by research projects from the D.G. de Calidad y Evaluación Ambiental from the Spanish Ministry of the Environment and the Plan Nacional de I+D from the Spanish Ministry of Education and Science (CGL2004-05984_C07-02/CLI, REN2001-0659-C03-03).
- Published
- 2006
133. Multi-platform in-situ and remote sensing techniques to derive Saharan dust properties during AMISOC-TNF 2013
- Author
-
Javier Andrey, Carmen Córdoba-Jabonero, Manuel Gil-Ojeda, José Antonio Adame, Emilio Cuevas, Mar Sorribas, and Laura Gómez
- Subjects
Troposphere ,In situ ,chemistry.chemical_compound ,Boundary layer ,Lidar ,Ozone ,chemistry ,Mineral dust ,Atmospheric sciences ,Multi platform ,Aerosol ,Remote sensing - Abstract
In the framework of AMISOC (Atmospheric Minor Species relevant to the Ozone Chemistry) project, a multiinstrumented campaign was performed in the Canary Islands area in summer-time from 01 July to 11 August 2013. Both ground-based remote-sensing and airborne in-situ measurements were performed under dust loading conditions. Saharan dusty (DD) conditions were reported during 57% of the overall campaign period. Particular DD cases corresponded to a 2-day period with a progressively arriving Saharan dust intrusion over Tenerife on 31 July (weak incidence) and 01 August (strong incidence). As reference, the non-dusty (ND) situation on 30 July was also examined. Vertical size distributions (SD) for particles within an extended fine-to-coarse (0.16-2.8 μm) mode were provided by using aircraft aerosol PCASP sonde measurements. Extinction profiles and Lidar ratio (LR) values were derived from Micro Pulse Lidar measurements. Despite no MAXDOAS aerosol profiling retrievals were available, the potential of this technique has also been introduced. A good agreement is found between the optical and microphysical properties, showing dust particles confined in a wide layer of around 4.5 km thickness from 1.5 to 6 km height. Dust incidence mostly affected the Free Troposphere (FT). LR ranged between 50 and 55 sr, showing typical values for Saharan dust particles. In general, the dust impact on mass concentration was enhanced due to the increase of larger particles, affecting both the Boundary layer (BL) and FT, but showing differences depending on the dusty case. MAXDOAS profiles are expected to be included in an extended version of this work.
- Published
- 2014
134. Characterisation of TSP and PM2.5 at Izaña and Sta. Cruz de Tenerife (Canary Islands, Spain) during a Saharan Dust Episode (July 2002)
- Author
-
S. Castillo, Andrés Alastuey, Carlos Torres, Miguel Escudero, Anna Avila, J. Pedro Diaz, Rita Van Dingenen, Omaira García, Pedro-Miguel Romero, Francisco J. Expósito, Emilio Cuevas, Jean Philippe Putaud, and Xavier Querol
- Subjects
Troposphere ,Atmospheric Science ,Meteorology ,Planetary boundary layer ,Dust storm ,Environmental science ,Relative humidity ,Mineral dust ,Atmospheric sciences ,Air quality index ,Chemical composition ,General Environmental Science ,Aerosol - Abstract
A strong African dust outbreak episode affecting the Canary Islands from 28 to 31/07/02 has been characterised at the Izana Observatory (IZO), located in the free troposphere (FT), and at Sta. Cruz de Tenerife (SCO), in the Marine Boundary Layer (MBL). The Saharan air mass intruded above the trade wind inversion layer resulting in daily mean PM levels of up to 616, 312, 98 and 26 μg m−3 of TSP, PM10, PM2.5 and PM1, respectively, at IZO. As demonstrated by the vertical sounding profiles, the MBL is compressed during the Saharan intrusion, favouring the deposition of coarse dust particles to the MBL and giving rise to daily levels of up to 85, 52 and 30 μg m−3 of PM10, PM2.5 and PM1, respectively, at SCO. A complete chemical and mineralogical characterisation has been performed for TSP and PM2.5 collected simultaneously at both sites. Levels of mineral elements increased during the Saharan episode at both sampling sites. In addition, at the MBL, the levels of the secondary inorganic aerosols registered during the Saharan episode were considerably higher than levels recorded during non-Saharan episodes. The partial formation of secondary coarse Ca and/or Na sulphates and nitrates by the reaction of gaseous pollutants (or derived oxidised phases), of a major local origin, with the natural aerosols has been deduced. These reactions may be favoured by the high concentration of coarse mineral and marine aerosols particles measured at SCO, the high relative humidity (RH) measured, as well as the strong compression of the MBL during the Saharan episode.
- Published
- 2005
135. Influence of major African dust intrusions on the 137Cs and 40K activities in the lower atmosphere at the Island of Tenerife
- Author
-
L. Karlsson, P.M. Romero-Campos, Emilio Cuevas, Silvia Alonso-Pérez, J. Hernández-Armas, and F. Hernandez
- Subjects
Atmospheric Science ,Radionuclide ,Limit value ,Air pollution ,Mineral dust ,medicine.disease_cause ,Atmospheric sciences ,Atmosphere ,Troposphere ,Oceanography ,Dust storm ,medicine ,Period (geology) ,Environmental science ,General Environmental Science - Abstract
The influence of two intensive low-altitude atmospheric-dust intrusions on the activity levels of 137Cs and 40K as well as atmospheric particle matter (PM10) concentrations in the lower atmosphere of the Canary Islands are analysed here. These two events took place at the beginning of January 2002 and March 2004, respectively. 3D atmospheric back-trajectories indicated that the main source of dust material involved in the considered atmospheric intrusions came from NW Africa. A consequence of these dust intrusions was the major increase of PM10 concentrations in the lower atmosphere. Both episodes were characterised by having weekly averages of PM10 concentration surpassing 150 μg m−3, higher than the daily PM10 limit value established by the EC/1999/30 directive for PM10 from 2005. Similarly, during these two events, both 137Cs and 40K activities increased by a factor of 6 and 13 as well as 13 and 14, respectively, over the basal values calculated for each radionuclide and time period (0.59±0.02 and 0.88±0.07 μBq m−3 as well as 12±6 and 24±8 μBq m−3).
- Published
- 2005
136. Transport pathways of ozone to marine and free-troposphere sites in Tenerife, Canary Islands
- Author
-
J. C. Guerra, C. Torres, Emilio Cuevas, and Sergio Rodríguez
- Subjects
Atmospheric Science ,Ozone ,Planetary boundary layer ,Air pollution ,Subsidence (atmosphere) ,Seasonality ,medicine.disease ,medicine.disease_cause ,Troposphere ,chemistry.chemical_compound ,Atmosphere of Earth ,chemistry ,Climatology ,medicine ,Environmental science ,Stratosphere ,General Environmental Science - Abstract
In this study we analysed two time series of surface ozone recorded in Tenerife: one in a marine environment (Aguere, in the marine boundary layer at 580 m.a.s.l.) and other in the free troposphere (Izana, above the trade wind inversion layer at 2367 m.a.s.l.). We performed a systematic 4-year analysis of ozone, backtrajectories and synoptic charts. The transport pathways of ozone for different O3 percentile (Pth) ranges were determined. At both sites, low ozone levels ( 90 Pth) occur from March to June, and are mainly associated with a subsiding transport pathway from the western side of lows developing over Western/Central Europe and the North Atlantic mid-latitudes. At Izana, high ozone events (>90 Pth) occur from April to August, and are associated with subsidence at the western edge of lows over the North Atlantic (very frequently at the W or SW of the Iberian Peninsula). The results of this study highlight the importance of the downward transport of ozone. High ozone events under meteorological scenarios classically associated with stratospheric intrusions have been recorded every year at the two sites. However, with our results we cannot ultimately determine if these high ozone events are caused by downward transport from the upper troposphere/lower stratosphere, or by lifting of continental ozone pollution and subsequent subsidence. The occurrence of high ozone events (>90 Pth) at Izana and not in Aguere during summer (when the trade wind inversion located between these sites reaches its strongest stage) is an evidence of the importance of the ozone downward supply from mid-upper troposphere in this region.
- Published
- 2004
137. Influence of African dust on the levels of atmospheric particulates in the Canary Islands air quality network
- Author
-
Emilio Cuevas, Xavier Querol, Sergio Rodríguez, Andrés Alastuey, and Mar Viana
- Subjects
Atmospheric Science ,geography ,geography.geographical_feature_category ,Meteorology ,Air pollution ,Particulates ,Mineral dust ,Atmospheric sciences ,medicine.disease_cause ,Urban area ,Aerosol ,medicine ,Environmental science ,Spatial variability ,Satellite imagery ,Air quality index ,General Environmental Science - Abstract
Time series of levels of atmospheric particulate matter (TSP and PM10) were studied at 19 air quality monitoring stations in the islands of Tenerife and Gran Canaria (Canary Islands) during the period 1998–2000. After analysing seasonal variations, attention was focused on the detection of high TSP and PM10 events and on the identification of their natural or anthropogenic origins. Back-trajectory analysis and TOMS-NASA aerosol index as well as satellite imagery (SeaWIFS-NASA) were used to identify three types of African dust outbreaks differing in seasonal occurrence, source origin and impact on TSP/PM10 levels. Mean annual and daily TSP and PM10 levels were compared with the forthcoming limit values of the EU Air Quality Directive EC/30/1999, and the results showed that the annual and daily limit values established for 2010 would only be met at rural stations. PM levels at urban background, urban and industrial sites would exceed the 2010 objectives. Only the levels at the urban-background stations would meet the requirements for 2005 despite the fact that the trade winds result in lower levels of atmospheric pollutants in the Canary Islands than in continental environments. The results highlight the role of African dust contributions when implementing the limit values of the EU directive.
- Published
- 2002
138. Quantifying Dry and Wet Deposition Fluxes in Two Regions of Contrasting African Influence: The NE Iberian Peninsula and the Canary Islands
- Author
-
Emilio Cuevas, Andrés Alastuey, Anna Avila, S. Castillo, Xavier Querol, Consejo Superior de Investigaciones Científicas (España), European Commission, and Ministerio de Economía, Industria y Competitividad (España)
- Subjects
inorganic chemicals ,Mediterranean climate ,Pollution ,Atmospheric Science ,010504 meteorology & atmospheric sciences ,Anthropogenic pollution ,media_common.quotation_subject ,Mineralogy ,010501 environmental sciences ,Environmental Science (miscellaneous) ,Mineral dust ,Dry deposition ,Atmospheric sciences ,01 natural sciences ,Atmosphere ,Polvo mineral ,Scavenging ,0105 earth and related environmental sciences ,media_common ,Particulates ,Material particulado ,Plume ,mineral dust ,dry deposition ,wet deposition ,African intrusions ,particulate matter ,anthropogenic pollution ,Contaminación antropogénica ,Deposition (aerosol physics) ,Wet deposition ,Environmental science ,Particulate matter - Abstract
This study considers the role of distance to the African source on the amount of deposition. To this end, dry and wet deposition was measured at a site close to Africa (Santa Cruz de Tenerife in the Canary Islands, SCO) and at a distant site located in NE Spain (La Castanya, Montseny, MSY). Because of the important influence of African influence on the buildup of particles in the atmosphere, we specifically addressed the contribution of North African events (NAF events) compared to other provenances (no-NAF events) in the wet and dry pathways at the two sites. At the site close to Africa, most of the crustal-derived elements were deposited in the dry mode, with NAF events contributing more than no-NAF events. Marine elements, by contrast, were mostly deposited at this site in the wet form with a predominance of no-NAF events. At MSY, wet deposition of SO4–S, NO3–N and NH4–N during NAF events was higher than at the site close to Africa, either in the wet or dry mode. This fact suggests that mineral dust interacts with pollutants, the mineral surface being coated with ammonium, sulphate and nitrate ions as the dust plume encounters polluted air masses in its way from North Africa to the Western Mediterranean. African dust may provide a mechanism of pollution scavenging and our results indicate that this removal is more effective in the wet mode at sites far away from the mineral source., We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI)., We acknowledge the financial support from the Spanish Government (CGL2005-07543-CLI, CGL2009-13188-C03-01, CSD2008-00040-Consolider Montes grants and the “Subprograma MICINN-PTA” funded by the European Social Fund). The Global Atmospheric Watch program at the Air Quality Research Observatory at Santa Cruz de Tenerife has been funded by AEMET. The IDAEA group acknowledges the financial support of the Generalitat de Catalunya (AGAUR 2014 SGR33 and the DGQA)
- Published
- 2017
139. Re-construction of global solar radiation time series from 1933 to 2013 at the Izaña Atmospheric Observatory
- Author
-
Emilio Cuevas, P. Pallé, Omaira García, A. M. de Frutos, Victoria E. Cachorro, Rosa Delia García, Juan José de Bustos, and P. M. Romero-Campos
- Subjects
Atmospheric Science ,Series (stratigraphy) ,Pyranometer ,Meteorology ,Mean squared error ,lcsh:TA715-787 ,media_common.quotation_subject ,lcsh:Earthwork. Foundations ,Atmospheric sciences ,lcsh:Environmental engineering ,Global solar radiation ,Sky ,Observatory ,Consistency (statistics) ,Sunshine duration ,Environmental science ,lcsh:TA170-171 ,media_common - Abstract
This paper presents the re-construction of the 80 year time series of daily global shortwave downward radiation (SDR) at the subtropical high-mountain Izaña Atmospheric Observatory (IZO, Spain). For this purpose, we combine SDR estimates from sunshine duration (SD) data using the Ångström–Prescott method over the 1933/1991 period, and SDR observations directly performed by pyranometers between 1992 and 2013. Since SDR measurements have been used as a reference, a strict quality control has been applied, when it was not possible data have been re-calibrated by using the LibRadtran model. By comparing to high quality SDR measurements, the precision and consistency over time of SDR estimations from SD data have successfully been documented. We obtain a overall root mean square error (RMSE) of 9.2% and an agreement between the variances of SDR estimations and SDR measurements within 92% (correlation coefficient of 0.96). Nonetheless, this agreement significantly increases when the SDR estimation is done considering different daily fractions of clear sky (FCS). In that case, RMSE is reduced by half, up to about 4.5%, when considering percentages of FCS > 40% (90% of days in the testing period). Furthermore, we prove that the SDR estimations can monitor the SDR anomalies in consistency with SDR measurements and, then, can be suitable for re-constructing solar radiation time series. The re-constructed IZO global SDR time series between 1933 and 2013 confirms discontinuities and periods of increases/decreases of solar radiation at Earth's surface observed at a global scale, such as the early brightening, dimming and brightening. This fact supports the consistency of the IZO SDR time series presented in this work, which may be a reference for solar radiation studies in the subtropical North Atlantic region.
- Published
- 2014
140. Recovering long-term aerosol optical depth series (1976–2012) from an astronomical potassium-based resonance scattering spectrometer
- Author
-
Emilio Cuevas, P. M. Romero, África Barreto, Christoph Wehrli, F. Almansa, P. Pallé, and C. Guirado
- Subjects
Atmospheric Science ,010504 meteorology & atmospheric sciences ,Contaminación atmosférica ,Solar irradiance ,01 natural sciences ,Aerosol optical depth ,Spectrometer ,Optics ,0103 physical sciences ,Calibration ,Aerosoles ,Helioseismology ,lcsh:TA170-171 ,010303 astronomy & astrophysics ,0105 earth and related environmental sciences ,Remote sensing ,Espectrómetros ,Radiometer ,business.industry ,lcsh:TA715-787 ,lcsh:Earthwork. Foundations ,Aerosol ,AERONET ,lcsh:Environmental engineering ,Wavelength ,13. Climate action ,Environmental science ,business - Abstract
A 37-year long-term series of monochromatic aerosol optical depth (AOD) has been recovered from solar irradiance measurements performed with the solar spectrometer Mark-I, deployed at Izaña mountain since 1976. The instrument operation is based on the method of resonant scattering, which affords wavelength absolute reference and stability (long-term stability and high precision) in comparison to other instruments based purely on interference filters. However, it has been specifically designed as a reference instrument for helioseismology, and its ability to determine AOD from transmitted and scattered monochromatic radiation at 769.9 nm inside a potassium vapour cell in the presence of a permanent magnetic field is evaluated in this paper. Particularly, the use of an exposed mirror arrangement to collect sunlight as well as the Sun–laboratory velocity dependence of the scattered component introduces some important inconveniences to overcome when we perform the instrument's calibration. We have solved this problem using a quasi-continuous Langley calibration technique and a refinement procedure to correct for calibration errors as well as for the fictitious diurnal cycle on AOD data. Our results showed similar calibration errors retrieved by means of this quasi-continuous Langley technique applied in different aerosol load events (from 0.04 to 0.3), provided aerosol concentration remains constant throughout the calibration interval. It assures the validity of this technique when it is applied in those periods with relatively high aerosol content. The comparative analysis between the recovered AOD data set from the Mark-I and collocated quasi-simultaneous data from the Cimel-AErosol RObotic NETwork (AERONET) and Precision Filter Radiometer (PFR) instruments showed an absolute mean bias ≤ 0.01 in the 10- and 12-year comparison, respectively. High correlation coefficients between AERONET and Mark-I and PFR/Mark-I pairs confirmed a very good linear relationship between instruments, proving that recovered AOD data series from Mark-I can be used together with PFR and AERONET AOD data to build a long-term AOD data series at the Izaña site (1976–now), suitable for future analysis of aerosols trends and inter-annual variability. Finally, the AOD preliminary trend analysis in the 29-year period from 1984 to 2012 with Mark-I AOD revealed no significant trends.
- Published
- 2014
141. Soil dust aerosols and wind as predictors of seasonal meningitis incidence in Niger
- Author
-
Carlos Perez Garcia Pando, Ron L. Miller, Michelle C. Stanton, Emilio Cuevas, Sylwia Trzaska, Pietro Ceccato, Jan P. Perlwitz, Peter J. Diggle, Madeleine C. Thomson, Pascal Yaka, and José María Baldasano
- Subjects
Predicción por métodos estadísticos ,Soil dust aerosols ,Climate ,Health, Toxicology and Mutagenesis ,Population ,wa_395 ,Wind ,Meningitis, Meningococcal ,Polvo atmosférico ,wc_245 ,Soil ,wl_200 ,Dry season ,parasitic diseases ,medicine ,Humans ,wd_600 ,Seasonal meningitis ,Meningitis ,Niger ,education ,Aerosols ,education.field_of_study ,Models, Statistical ,Ecology ,Harmattan ,Research ,Incidence ,Incidence (epidemiology) ,Public Health, Environmental and Occupational Health ,Dust ,medicine.disease ,Geography ,Climatology ,Linear Models ,Meningococcal meningitis ,Climate model ,Seasons ,Forecasting ,Dust emission - Abstract
Background: Epidemics of meningococcal meningitis are concentrated in sub-Saharan Africa during the dry season, a period when the region is affected by the Harmattan, a dry and dusty northeasterly trade wind blowing from the Sahara into the Gulf of Guinea. Objectives: We examined the potential of climate-based statistical forecasting models to predict seasonal incidence of meningitis in Niger at both the national and district levels. Data and methods: We used time series of meningitis incidence from 1986 through 2006 for 38 districts in Niger. We tested models based on data that would be readily available in an operational framework, such as climate and dust, population, and the incidence of early cases before the onset of the meningitis season in January–May. Incidence was used as a proxy for immunological state, susceptibility, and carriage in the population. We compared a range of negative binomial generalized linear models fitted to the meningitis data. Results: At the national level, a model using early incidence in December and averaged November–December zonal wind provided the best fit (pseudo-R2 = 0.57), with zonal wind having the greatest impact. A model with surface dust concentration as a predictive variable performed indistinguishably well. At the district level, the best spatiotemporal model included zonal wind, dust concentration, early incidence in December, and population density (pseudo-R2 = 0.41). Conclusions: We showed that wind and dust information and incidence in the early dry season predict part of the year-to-year variability of the seasonal incidence of meningitis at both national and district levels in Niger. Models of this form could provide an early-season alert that wind, dust, and other conditions are potentially conducive to an epidemic. Citation: Pérez García-Pando C, Stanton MC, Diggle PJ, Trzaska S, Miller RL, Perlwitz JP, Baldasano JM, Cuevas E, Ceccato P, Yaka P, Thomson MC. 2014. Soil dust aerosols and wind as predictors of seasonal meningitis incidence in Niger. Environ Health Perspect 122:679–686; http://dx.doi.org/10.1289/ehp.1306640
- Published
- 2014
142. Coulomb interactions in Anderson insulators
- Author
-
Emilio Cuevas, Anastasio Díaz-Sánchez, Miguel Ortuño, and J. Talamantes
- Subjects
Tunnel effect ,Condensed matter physics ,Chemistry ,Metallic electrode ,General Chemical Engineering ,Coulomb ,General Physics and Astronomy ,Conductance ,Relaxation (physics) ,Quantum Hall effect ,Condensed Matter::Disordered Systems and Neural Networks ,Anderson impurity model ,Quantum tunnelling - Abstract
We review the main theoretical aspects concerning Coulomb glasses, that is systems with states localized by disorder and long-range interactions between their particles. The numerical algorithms available for their simulations are explained. We analyse tunnelling experiments and the role of screening by metallic electrodes. We study the mechanism for variable-range hopping conductance in these systems and in particular the role of many-electron correlations. Recent relaxation experiments and the possible glass transitions are reviewed. Finally, we describe different approaches to incorporate quantum effects in the study of Coulomb glasses.
- Published
- 2001
143. Phase Transition in Coulomb Glasses
- Author
-
Anastasio Díaz-Sánchez, Antonio Pérez-Garrido, Miguel Ortuño, and Emilio Cuevas
- Subjects
Quantum phase transition ,Physics ,Phase transition ,Condensed matter physics ,Coulomb ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials - Published
- 2000
144. Behavior of NO2and O3columns during the eclipse of February 26, 1998, as measured by visible spectroscopy
- Author
-
Olga Puentedura, Emilio Cuevas, Manuel Gil, and Margarita Yela
- Subjects
Atmospheric Science ,Ecology ,Solar eclipse ,Differential optical absorption spectroscopy ,Solar zenith angle ,Paleontology ,Soil Science ,Forestry ,Aquatic Science ,Oceanography ,Atmospheric sciences ,Solar physics ,Occultation ,Fraunhofer lines ,symbols.namesake ,Geophysics ,Space and Planetary Science ,Geochemistry and Petrology ,Earth and Planetary Sciences (miscellaneous) ,symbols ,Environmental science ,Stratosphere ,Earth-Surface Processes ,Water Science and Technology ,Eclipse - Abstract
Observations of the NO2 and O3 columns using zenith-viewing differential absorption spectroscopy in the visible range (450–540 nm) were carried out at Izana Observatory (Tenerife, 28°N, 16°W, 2370 m above sea level.) during the eclipse of February 26, 1998 (95% occultation over the station). Ozone has been retrieved using two different spectral ranges to minimize the effect of the continuous change of the solar spectrum shape as the Sun is being occulted. Small variations before the maximum phase in agreement with previous observations are found, but because of the change in the shape of the solar spectrum, it cannot conclusively be determined whether the ozone changes are real or due to interferences with changing Fraunhofer lines. The difficulties in observing small changes of absorbing gases during solar eclipse when using remote sensing technique that uses the solar UV and visible radiation as the source are discussed. NO2 displays an increase in phase with the degree of solar occultation, as compared to a non eclipse day of 1.55±0.09. A simple model assuming that changes over short times scales are only due to changes in photodissociation, using O3 and temperatures obtained from an ozone sounding station close to the observatory, reproduces the observed variation when the NO2 bulk is assumed to be at an altitude of 28 km. Correction for differences between local solar zenith angle (SZA) and the SZA where the absorption takes place is taken into account.
- Published
- 2000
145. Critical Spectral Statistics in Two-Dimensional Interacting Disordered Systems
- Author
-
Emilio Cuevas
- Subjects
Physics ,Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed matter physics ,Spectral statistics ,Spectral properties ,FOS: Physical sciences ,General Physics and Astronomy ,Interaction strength ,Disordered Systems and Neural Networks (cond-mat.dis-nn) ,Fermion ,Condensed Matter - Disordered Systems and Neural Networks ,Condensed Matter::Disordered Systems and Neural Networks ,Universality (dynamical systems) ,Delocalized electron ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,Coulomb ,Scaling - Abstract
The effect of Coulomb and short-range interactions on the spectral properties of two-dimensional disordered systems with two spinless fermions is investigated by numerical scaling techniques. The size independent universality of the critical nearest level-spacing distribution $P(s)$ allows one to find a delocalization transition at a critical disorder $W_{\rm c}$ for any non-zero value of the interaction strength. At the critical point the spacings distribution has a small-$s$ behavior $P_c(s)\propto s$, and a Poisson-like decay at large spacings., 4 two-column pages, 3 eps figures, RevTeX, new results added
- Published
- 1999
146. Numerical study of relaxation in electron glasses
- Author
-
Miguel Ortuño, Anastasio Díaz-Sánchez, Emilio Cuevas, and Antonio Pérez-Garrido
- Subjects
Physics ,Low energy ,Strongly Correlated Electrons (cond-mat.str-el) ,Condensed matter physics ,Baja enegía ,Relaxation (NMR) ,Temperature ,FOS: Physical sciences ,Proceso de relajación ,Disordered Systems and Neural Networks (cond-mat.dis-nn) ,Radius ,Electron ,Condensed Matter - Disordered Systems and Neural Networks ,Temperatura ,Crystals ,Power law ,Exponential function ,Condensed Matter - Strongly Correlated Electrons ,Cristales ,Física Aplicada ,Exponent ,Coulomb ,Strongly correlated material ,Relaxation process - Abstract
We perform a numerical simulation of energy relaxation in three-dimensional electron glasses in the strongly localized regime at finite temperatures. We consider systems with no interactions, with long-range Coulomb interactions and with short-range interactions, obtaining a power law relaxation with an exponent of 0.15, which is independent of the parameters of the problem and of the type of interaction. At very long times, we always find an exponential regime whose characteristic time strongly depends on temperature, system size, interaction type and localization radius. We extrapolate the longest relaxation time to macroscopic sizes and, for interacting samples, obtain values much larger than the measuring time. We finally study the number of electrons participating in the relaxation processes of very low energy configurations., Comment: 6 eps figures. To be published in Phys. Rev. B
- Published
- 1999
147. Trends of ozone in the troposphere
- Author
-
J. A. Lathrop, Douglas S. Shadwick, Hiram Levy, H. E. Scheel, Hans Claude, David W. Tarasick, C. P. Meyer, Volker A. Mohnen, A. S. Lefohn, Joyce M. Harris, F. J. Schmidlin, Osamu Uchino, Samuel J. Oltmans, Emilio Cuevas, Beverly J. Johnson, E.-G. Brunke, Ian E. Galbally, and James B. Kerr
- Subjects
Ozone ,Northern Hemisphere ,Atmospheric sciences ,Latitude ,Troposphere ,chemistry.chemical_compound ,Geophysics ,chemistry ,Climatology ,Middle latitudes ,General Earth and Planetary Sciences ,Environmental science ,Tropospheric ozone ,Southern Hemisphere ,Stratosphere - Abstract
Using a set of selected surface ozone (nine stations) and ozone vertical profile measurements (from six stations), we have documented changes in tropospheric ozone at a number of locations. From two stations at high northern hemisphere (NH) latitudes there has been a significant decline in ozone amounts throughout the troposphere since the early 1980s. At midlatitudes of the NH where data are the most abundant, on the other hand, important regional differences prevail. The two stations in the eastern United States show that changes in ozone concentrations since the early 1970s have been relatively small. At the two sites in Europe, however, ozone amounts increased rapidly into the mid-1980s, but have increased less rapidly (or in some places not at all) since then. Increases at the Japanese ozonesonde station have been largest in the lower troposphere, but have slowed in the recent decade. The tropics are sparsely sampled but do not show significant changes. Small increases are suggested at southern hemisphere (SH) midlatitudes by the two surface data records. In Antarctica large declines in the ozone concentration are noted in the South Pole data, and like those at high latitudes of the NH, seem to parallel the large decreases in the stratosphere.
- Published
- 1998
148. Global quantum fluctuations in metallic particles
- Author
-
J. A. Vergés, Enrique Louis, Miguel Ortuño, and Emilio Cuevas
- Subjects
Physics ,Condensed matter physics ,Chaotic ,Metal ,symbols.namesake ,Autoionization ,Atomic orbital ,visual_art ,Quantum mechanics ,symbols ,visual_art.visual_art_medium ,Quantum system ,Hamiltonian (quantum mechanics) ,Quantum ,Quantum fluctuation - Abstract
Departamento de Fi´sica, Universidad de Murcia, E-30080 Murcia, Spain~Received 12 May 1997!A model of three-dimensional quantum chaotic billiards is used to investigate global quantum fluctuations inmetallic particles. The quantum system is described by means of a tight-binding Hamiltonian in which theenergies of the orbitals at the surface sites are chosen at random in the range (2W/2,W/2). The results indicatethat for reasonable values of W ~on the order of half the bandwidth! the energy fluctuations of the highestoccupied level are much larger than the corresponding average interlevel spacing. This provides a naturalexplanation for autoionization effects in granular metals. @S0163-1829~97!51436-6#
- Published
- 1997
149. Traversal Time as a Function of the Size of the Wavepacket
- Author
-
Emilio Cuevas, Vladimir Gasparian, Miguel Ortuño, and J. Ruiz
- Subjects
Superluminal motion ,business.industry ,Wave packet ,Gaussian ,General Engineering ,Statistical and Nonlinear Physics ,Function (mathematics) ,Electromagnetic radiation ,Computational physics ,Tree traversal ,symbols.namesake ,Optics ,symbols ,Wavenumber ,Transmission coefficient ,business ,Mathematics - Abstract
We calculate numerically the transmission coefficient and the traversal time for finite Gaussian wavepackets as a function of their widths. We consider electromagnetic waves crossing a slab and a periodic structure. We find that the periodic structure can be crossed at superluminal velocities for wavenumbers in the optical gap and sizes larger than the thickness of the system. The corresponding transmission coefficients are very small. The long wavepacket limit of the traversal time coincides with previous analytical results for the real component of the interaction time. The imaginary component of this time only affects the change in size of the wavepacket.
- Published
- 1997
150. Conductivity of the two-dimensional Coulomb glass
- Author
-
J. Ruiz, Miguel Ortuño, Antonio Pérez-Garrido, Emilio Cuevas, and Michael Pollak
- Subjects
Many-body problem ,Physics ,Condensed matter physics ,Electronic correlation ,Electrical resistivity and conductivity ,Coulomb ,Conductivity ,Atomic physics ,Approx ,Fermi gas ,Anderson impurity model - Abstract
We studied by computer simulation the effects of Coulomb interactions on the properties of strongly localized Anderson insulators. We took full account of many-body effects by considering the many-electron configurations of the system rather than single-particle states. We developed an algorithm to obtain the configurations and energies of the low-lying system states, and from there the conductivity. At low-temperatures T, we found that the conductivity was proportional to exp({minus}T{sub 0}/T){sup 1/2}. Many-electron transitions were seen to be important at very low temperatures. In this regime, T{sub 0}{approx}0.61, which is much smaller than predicted by one-electron theory. Experimental results which use the predicted T{sub 0} to obtain localization radii must therefore be reinterpreted. {copyright} {ital 1997} {ital The American Physical Society}
- Published
- 1997
Catalog
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.