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Moreira M.A.,Polytechnic Institute of Lisbon | Moreira M.A.,Instituto Dom Luis | Geoffroy L.,CNRS Oceanic Domains Laboratory | Pozzi J.P.,CNRS ENS Geology Laboratory
Journal of Geophysical Research B: Solid Earth | Year: 2015

The localization of magma melting areas at the lithosphere bottom in extensional volcanic domains is poorly understood. Large polygenetic volcanoes of long duration and their associated magma chambers suggest that melting at depth may be focused at specific points within the mantle. To validate the hypothesis that the magma feeding a mafic crust, comes from permanent localized crustal reservoirs, it is necessary to map the fossilized magma flow within the crustal planar intrusions. Using the AMS, we obtain magmatic flow vectors from 34 alkaline basaltic dykes from São Jorge, São Miguel and Santa Maria islands in the Azores Archipelago, a hot-spot related triple junction. The dykes contain titanomagnetite showing a wide spectrum of solid solution ranging from Ti-rich to Ti-poor compositions with vestiges of maghemitization. Most of the dykes exhibit a normal magnetic fabric. The orientation of the magnetic lineation k1 axis is more variable than that of the k3 axis, which is generally well grouped. The dykes of São Jorge and São Miguel show a predominance of subhorizontal magmatic flows. In Santa Maria the deduced flow pattern is less systematic changing from subhorizontal in the southern part of the island to oblique in north. These results suggest that the ascent of magma beneath the islands of Azores is predominantly over localized melting sources and then collected within shallow magma chambers. According to this concept, dykes in the upper levels of the crust propagate laterally away from these magma chambers thus feeding the lava flows observed at the surface. © 2014. American Geophysical Union. All Rights Reserved.


Mogo S.,University of Beira Interior | Mogo S.,University of Valladolid | Mogo S.,Instituto Dom Luis | Cachorro V.,University of Valladolid | de Frutos A.,University of Valladolid
Optica Pura y Aplicada | Year: 2011

Since October 2009 an aerosol measurement data set was started at Covilhã, a small town located in the region of Beira Interior (Portugal) in the interior of the Iberian Peninsula. Until July 2010, the ambient light-absorption coefficient, σ α (470 nm), σ α (522 nm) and σ α (660 nm), presented a daily mean value of 14.2Mm -1 (StD=8.6Mm -1), 12.1Mm -1 (StD=7.3Mm -1) and 9.6Mm -1 (StD=5.7Mm -1), respectively. Monthly variations and daily cycle are presented in this work. © Sociedad Española de Óptica.


Mogo S.,University of Valladolid | Mogo S.,University of Beira Interior | Mogo S.,Instituto Dom Luis | Cachorro V.E.,University of Valladolid | And 7 more authors.
Atmospheric Chemistry and Physics | Year: 2012

In situ measurements of aerosol optical properties and particle size distributions were made in the summer of 2008 at the ALOMAR station facility (69°16' N, 16°00' E), located in a rural site in the north of the island of Andøya (Vesterälen archipelago), approximately 300 km north of the Arctic Circle. The extended three-month campaign was part of the POLARCAT Project (Polar Study using Aircraft, Remote Sensing, Surface Measurements and Models, of Climate, Chemistry, Aerosols, and Transport) of the International Polar Year (IPY-2007-2008). Our goal was to characterize the aerosols of this sub-Arctic area, which are frequently transported to the Arctic region. Data from 13 June to 26 August 2008 were available and the statistical data for all instruments were calculated based on the hourly averages. The overall data coverage was approximately 72%. The hourly mean values of the light-scattering coefficient, σs, and the light-absorption coefficient, σa, at 550 nm were 5.41 Mm-1 (StD Combining double low line 3.55 Mm-1) and 0.40 Mm-1 (StD Combining double low line 0.27 Mm-1), respectively. The scattering/absorption Ångström exponents, αs,a, were used in a detailed analysis of the variations of the spectral shape of σs,a. While αs indicates the presence of two particle sizes corresponding to two types of aerosols, αa indicates only one type of absorbing aerosol particle. αa values greater than 1 were not observed. The single-scattering albedo, ω0, ranged from 0.62 to 0.99 (mean Combining double low line 0.91, StD Combining double low line 0.05), and the relationships between this parameter and the absorption/scattering coefficients and the Ångström exponents are presented. Any absorption value may lead to the lowest values of ω0, whereas only the lowest scattering values were observed in the lowest range of ω0. For a given absorption value, lower ω0 were observed for smaller αs. The submicrometer, micrometer and total concentrations of the particles presented hourly mean values of 1277 cm-3 (StD Combining double low line 1563 cm-3), 1 cm -3 (StD Combining double low line 1 cm-3) and 2463 cm -3 (StD Combining double low line 4251 cm-3), respectively, and the modal correlations were also investigated. The optical and microphysical parameters, as well as their relationship with each other, are reported. σs correlated strongly with the number concentration of accumulation mode particles and more strongly with the micrometer fraction of particles, but weak correlations were observed for the Aitken and nucleation modes. The origins and pathways of the air masses were examined, and based on sector classification, a relationship between the air mass origin, the optical parameters and the size distributions was established. The low values of the optical and microphysical parameters indicate that the predominant regional aerosol is mostly clean and the shape of the size distribution is characterized by bimodal median size distributions. However, the relationships between the air mass origins and the parameters studied allow us to describe two characteristic situations: the one of the northern and western air masses, which were predominantly composed of marine aerosols and presented the lowest optical and microphysical values observed, indicating predominantly non-absorbent and coarser particles; and the one of the eastern and southern air masses, in which continental aerosols were predominant and exhibited higher values for all parameters, indicating the presence of smaller absorbent particles. The north-northeastern air masses presented the strongest Aitken mode, indicating more recently formed particles, and the southeastern air masses presented the strongest accumulation mode (however, the southeastern air masses were the least common, accounting for only 3% of occurrences). © 2012 Author(s).


Mogo S.,University of Valladolid | Mogo S.,University of Beira Interior | Mogo S.,Instituto Dom Luis | Cachorro V.E.,University of Valladolid | de Frutos A.M.,University of Valladolid
Journal of Environmental Management | Year: 2012

In this work, a novel technique is used to estimate the aerosol complex index of refraction of in situ collected samples. Samples of atmospheric particulate matter were collected in El Arenosillo, southern Spain, on polycarbonate filters during summer 2004 as part of an aerosol characterization campaign. These samples were analyzed for the volumetric absorption coefficient in the 320-800 nm spectral region and an estimation of the effective imaginary refractive index was made. The values of the imaginary part of the complex refractive index ranged between 0.0009-0.0215 at 800 nm and 0.0015-0.0114 at 320 nm. Little dependence on the wavelength was observed. Several intense and long lasting desert outbreaks were registered during the campaign and the complex refractive index almost doubles its value during these dust events. Finally, we present a comparison of data obtained in situ with columnar data obtained from the AERONET network. A correlation factor of 0.64 was obtained between both data, which gives an idea of how accurately the in situ ground data represent the total column. © 2012 Elsevier Ltd.


Mogo S.,University of Valladolid | Mogo S.,University of Beira Interior | Mogo S.,Instituto Dom Luis | Cachorro V.E.,University of Valladolid | And 4 more authors.
AIP Conference Proceedings | Year: 2013

During the 2008 summer, a field campaign was carried out at the Arctic Lidar Observatory for Middle Atmosphere Research, ALOMAR, on Andoya island close to the town of Andenes (69° 16'N, 16° 00'E, 380 m a.s.l.), approximately 300 km north of the Arctic Circle. The campaign was part of the contribution of the Atmospheric Optics Group of the Valladolid University (GOA-UVa) to the International Polar Year, in the framework of the POLARCAT (Polar Study using Aircraft, Remote Sensing, Surface Measurements and Models of Climate, Chemistry, Aerosols, and Transport) project. This GOA-UVa's field campaign has been developed to obtain experimental data for local aerosols, its optical characteristics (absorption / scattering coefficients and single scattering albedo), its size distributions and derived parameters. For this purpose, different instruments were simultaneously installed in the station facilities. These are the first measurements with this variety of information reported in the station and can be extrapolated over a wide area around. © 2013 AIP Publishing LLC.


Mogo S.,University of Valladolid | Mogo S.,University of Beira Interior | Mogo S.,Instituto Dom Luis | Cachorro V.E.,University of Valladolid | And 2 more authors.
Journal of Environmental Monitoring | Year: 2012

A field campaign was conducted from October 2009 to July 2010 at Covilhã, a small town located in the region of Beira Interior (Portugal) in the interior of the Iberian Peninsula. The ambient light-absorption coefficient, σa (522 nm), obtained from a Particle Soot Absorption Photometer (PSAP), presented a daily mean value of 12.1 Mm -1 (StD = 7.3 Mm-1). The wavelength dependence of aerosol light absorption is investigated through the Ångström parameter, αa. The αa values for the pair of wavelengths 470-660 nm ranged from 0.86 to 1.47 during the period of measurements. The PSAP data were used to infer the mass of light absorbing carbon (LAC) and the daily mean varied from 0.1 to 6.8 μg m-3. A detailed study of special events with different aerosol characteristics is carried out and, to support data interpretation, air masses trajectory analysis is performed. © The Royal Society of Chemistry 2012.


Barja B.,Centro Meteorologico Of Camaguey | Mogo S.,University of Valladolid | Mogo S.,University of Beira Interior | Mogo S.,Instituto Dom Luis | And 5 more authors.
Environmental Sciences: Processes and Impacts | Year: 2013

Atmospheric aerosol particles were collected at Camagüey, Cuba, during the period from February 2008 to April 2009 in order to know the particulate matter levels (PM) together with a general chemical and absorption characterization. The aerosols collection was carried out with a low volume particulate impactor twice a week. Gravimetric analysis of the particulate matter fractions PM10 and PM1 was carried out. An analysis of the eight major inorganic species (Na+, K+, Ca2+, Mg 2+, NH4 +, Cl-, NO3 - and SO4 2-) using ionic chromatography was conducted. The results were analyzed in two periods, the high aerosol concentration period (May to August) and the period with low aerosol concentration (the other months). During the high concentration period the average PM10 and PM1 levels were 35.11 μg m-3 (std = 15.45 μg m-3) and 16.86 μg m-3 (std = 6.14 μg m -3). During the low concentration period the average PM10 and PM1 levels were 23.13 μg m-3 (std = 5.00 μg m-3) and 13.00 μg m-3 (std = 4.02 μg m-3). For both periods, Cl-, Na+ and NO3 - are the predominant species in the coarse fraction (PM1-10), and SO4 2-and NH4 + are the predominant species in the fine fraction (PM1). The spectral aerosol absorption coefficient, σa, was measured for the wavelength range 400-700 nm with 10 nm steps. The σa values were obtained with a filter transmission method for the fine fraction and were evaluated for 54 days covering a wide range of atmospheric conditions including a Saharan dust intrusion. σa ranges from 8.5 M m-1 to 34.5 M m-1 at a wavelength of 550 nm, with a mean value of 18.7 M m-1. The absorption Ångström parameter, αa, calculated for the pair of wavelengths (450/700 nm) presents a mean value of 0.33 (std = 0.19), which is a very low value comparing with those that can be found in the bibliography. Although the sampling period is short, these data represent the first evaluation of PM values with their chemical and optical absorption characterization in Cuba. In addition to the regional interest, the presented values can be directly used by those working with absorption, forcing by aerosols and radiative transfer calculations in general. Also, these data can be used as input in Global Climate Models. © 2013 The Royal Society of Chemistry.


Carvalho J.,National Laboratory of Energy and Geology | Matias H.,Repsol | Matias H.,Instituto Dom Luis | Rabeh T.,National Research Institute of Astronomy and Geophysics | And 4 more authors.
Tectonophysics | Year: 2012

The Algarve is located a few hundred kilometres north of the crossing of the E-W Eurasia-Africa plate boundary and is characterised by a moderate seismicity, with some important historical and instrumental earthquakes causing loss of lives and significant material damages. The area is affected not only by plate boundary generated earthquakes but also by local events capable of generating moderate to large earthquakes. The assessment of onshore local sources and its connections with the plate border is therefore of vital importance for an evaluation of the regional seismic hazard. This paper discusses the application of geophysical data to study a large fault zone which is the offshore prolonging of the Carcavai fault zone (CF), an onshore outcropping structure more than 20. km long which is seen to deform sediments of Plio-Quaternary age. Offshore and onshore aeromagnetic data, offshore gravimetric and seismic reflection data shows the existence of a long (over 200. km) WSW-ENE trending fault zone affecting the Palaeozoic basement with a normal geometry which is probably segmented by NNW-SSE to N-S faults. Seismic data shows that this fault zone has been reactivated as a left-lateral strike-slip fault and inverted in the Cenozoic with the upthrust of the northwestern block, in agreement with the onshore CF characteristics. Recent work carried out onshore and offshore near the coastline that shows deformation of Plio-Quaternary sediments suggests that this is an active fault. Some of the faults segments have instrumental seismicity associated. Though faults very rarely rupture along its entire length, several fault segments have a length of about 30. km and may produce an earthquake of magnitude about7. The proximity of the onshore segment to the city of Faro and of the offshore segments to the main population centres of the Algarve makes it a serious threat to the Algarve. © 2012 Elsevier B.V.

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