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Trigo I.F.,Instituto Portugues Do Mar e da Atmosfera IPMA | Trigo I.F.,Instituto Dom Luiz IDL | Boussetta S.,ECMWF | Viterbo P.,Instituto Portugues Do Mar e da Atmosfera IPMA | And 4 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2015

The coupling between land surface and the atmosphere is a key feature in Earth System Modeling for exploiting the predictability of slowly evolving geophysical variables (e.g., soil moisture or vegetation state), and for correctly representing rapid variations within the diurnal cycle, particularly relevant in data assimilation applications. In this study, land surface temperature (LST) estimated from Meteosat Second Generation (MSG) is used to assess the European Centre for Medium-Range Weather Forecasts (ECMWF) skin temperature, which can be interpreted as a radiative temperature of the model surface. It is shown that the ECMWF model tends to slightly overestimate skin temperature during nighttime and underestimate daytime values. Such underestimation of daily amplitudes is particularly pronounced in (semiarid) arid regions, suggesting a misrepresentation of surface energy fluxes in those areas. The LST estimated from MSG is used to evaluate the impact of changes in some of the ECMWF model surface parameters. The introduction of more realistic model vegetation is shown to have a positive but limited impact on skin temperature: long integration leads to an equilibrium state where changes in the latent heat flux and soil moisture availability compensate each other. Revised surface roughness lengths for heat and momentum, however, lead to overall positive impact on daytime skin temperature, mostly due to a reduction of sensible heat flux. This is particularly relevant in nonvegetated areas, unaffected by model vegetation. The reduction of skin conductivity, a parameter which controls the heat transfer to ground by diffusion, is shown to further improve the model skin temperature. Key Points Remote sensing land surface temperature used to assess ECMWF skin temperature Use of monthly LAI has limited impact on model skin temperature Revised surface roughness lengths reduce skin temperature bias in arid regions. © 2015. American Geophysical Union. All Rights Reserved.

Jesus A.P.,German University of Technology in Oman | Jesus A.P.,Instituto Dom Luiz IDL | Mateus A.,Instituto Dom Luiz IDL | Mateus A.,University of Lisbon | And 6 more authors.
Tectonophysics | Year: 2016

The Beja Layered Gabbroic Sequence (LGS) is a mafic, layered synorogenic intrusion that was emplaced at the SW border of the Ossa Morena Zone (OMZ) at ca. 350 Ma during the early stages of the Variscan oblique continental collision. The LGS represents the primitive member of the Beja Igneous Complex (BIC), which records part of an important Variscan magmatic event to the north of the SW Iberian suture that led to the formation of several igneous complexes. Although LGS primary magmatic features are well-preserved from post-crystallization tectono-metamorphic events, the magma chamber processes were influenced by the Variscan regional stress field which affected also the development of the magmatic layering and associated foliation. The baric evolution recorded in LGS (from 9 to 4 kbar) is compatible with early crustal underplating of juvenile basaltic magma at the Moho. Mild lower crustal contamination resulted in Nb-Ta-Rb-Th depletion and higher REE fractionation compared to MORB. Contamination proceeded mainly by assimilation-fractional-crystallization (AFC) at final level of emplacement. The obtained results suggest that the spatially associated BIC mesocratic rocks are genetically related to LGS, both deriving from an equivalent mantle source. It is proposed that the underplating of basaltic magmas at the lower crust gave rise to a deep crustal hot zone. This allows BIC evolution to be explained as a single, long-lived magmatic event of progressive geochemical and lithological diversification due to the involvement of distinct crustal components. The most important components were incorporated at depth by the reworking of OMZ lower crustal rocks, with the involvement of middle crustal rocks later on, and of upper crustal contamination during the final stages of emplacement. © 2016 Elsevier B.V.

Hernandez-Molina F.J.,Royal Holloway, University of London | Sierro F.J.,University of Salamanca | Llave E.,Instituto Geologico Y Minero Of Espana Igme | Roque C.,Instituto Dom Luiz IDL | And 10 more authors.
Marine Geology | Year: 2015

The contourite depositional system (CDS) along the southwestern Iberian Margin (SIM), within the Gulf of Cadiz and offshore areas of western Portugal bear the unmistakable signal of Mediterranean Outflow Water (MOW) exiting the Strait of Gibraltar. This locality records key information concerning the effects of tectonic activity on margin sedimentation, the effects of MOW dynamics on Atlantic circulation, and how these factors may have influenced global climate. Over the last four decades, numerous studies have been conducted on the late Miocene, Pliocene and Quaternary sedimentary stacking pattern of Neogene basins along the SIM for both academic and resources exploration purposes. However, understanding of the region rests primarily on basic seismic stratigraphy calibrated with limited data from only a few exploration wells. The Integrated Ocean Drilling Program (IODP) Expedition 339 recently drilled five sites in the Gulf of Cadiz and two sites on the western Iberian margin. The integration of core and borehole data with other geophysical databases leads us to propose a new stratigraphic framework. Interpretation of IODP Exp. 339 data along with that from industry sources and onshore outcrop analysis helps refine our understanding of the SIM's sedimentary evolution.We identify significant changes in sedimentation style and dominant sedimentary processes, coupled with widespread depositional hiatuses along the SIM within the Cadiz, Sanlucar, Doñana, Algarve and Alentejo basins. Following the 4.5. Ma cessation of a previous phase of tectonic activity related to the Miocene-Pliocene boundary, tectonics continued to influence margin development, downslope sediment transport and CDS evolution. Sedimentary features indicate tectonic pulses of about 0.8-0.9. Ma duration with a pronounced overprint of ~. 2-2.5. Ma cycles. These more protracted cycles relate to the westward rollback of subducted lithosphere at the convergent Africa-Eurasia plate boundary as its previous NW-SE compressional regime shifted to a WNW-ESE direction. Two major compressional events affecting to the Neogene basins at 3.2-3. Ma and 2-2.3. Ma help constrain the three main stages of CDS evolution. The stages include: 1) the initial-drift stage (5.33-3.2. Ma) with a weak MOW, 2) a transitional-drift stage (3.2-2. Ma) and 3) a growth-drift stage (2. Ma-present time) with enhanced MOW circulation into the Atlantic and associated contourite development due to greater bottom-current velocity. Two minor Pleistocene discontinuities at 0.7-0.9. Ma and 0.3-0.6. Ma record the effects of renewed tectonic activity on basin evolution, appearing most prominently in the Doñana basin. Several discontinuities bounding major and minor units appear on seismic profiles. Quaternary records offer the clearest example of this, with major units of about 0.8-0.9. Ma and sub-units of 0.4-0.5. Ma. Sedimentation is controlled by a combination of tectonics, sediment supply, sea-level and climate. This research identifies time scales of tectonic controls on deep-marine sedimentation, specifically over periods of 2.5→. 0.4. Ma. Shorter-term climatic (orbital) mechanisms control sedimentation at time scales of ≤. 0.4. Ma. The role of bottom water circulation and associated processes in shaping the seafloor and controlling the sedimentary stacking pattern on continental margins has to be seriously reconsidered in future multidisciplinary studies. This is not only because of the common occurrence of sandy contourite deposits in deep water setting and their economic interest for hydrocarbon exploration, but principally because they archive the heartbeat of the interior Earth and therefore have important sedimentary and paleoceanographic implications. © 2015 The Authors.

Matos C.,Instituto Dom Luiz IDL | Silveira G.,Instituto Dom Luiz IDL | Silveira G.,Polytechnic Institute of Lisbon | Matias L.,Instituto Dom Luiz IDL | And 8 more authors.
Journal of Volcanology and Geothermal Research | Year: 2015

We present the first image of the Madeira upper crustal structure, using ambient seismic noise tomography. 16. months of ambient noise, recorded in a dense network of 26 seismometers deployed across Madeira, allowed reconstructing Rayleigh wave Green's functions between receivers. Dispersion analysis was performed in the short period band from 1.0 to 4.0. s. Group velocity measurements were regionalized to obtain 2D tomographic images, with a lateral resolution of 2.0. km in central Madeira. Afterwards, the dispersion curves, extracted from each cell of the 2D group velocity maps, were inverted as a function of depth to obtain a 3D shear wave velocity model of the upper crust, from the surface to a depth of 2.0. km. The obtained 3D velocity model reveals features throughout the island that correlates well with surface geology and island evolution. © 2015 Elsevier B.V.

Silveira G.,Instituto Dom Luiz IDL | Silveira G.,Polytechnic Institute of Lisbon | Afonso Dias N.,Instituto Dom Luiz IDL | Afonso Dias N.,Polytechnic Institute of Lisbon | Villasenor A.,CSIC - Institute of Earth Sciences Jaume Almera
Tectonophysics | Year: 2013

We present new Rayleigh-wave dispersion maps of the western Iberian Peninsula for periods between 8 and 30. s, obtained from correlations of seismic ambient noise, following the recent increase in seismic broadband network density in Portugal and Spain. Group velocities have been computed for each station pair using the empirical Green's functions generated by cross-correlating one-day-length seismic ambient-noise records. The resulting high-path density allows us to obtain lateral variations of the group velocities as a function of period in cells of 0.5°. ×. 0.5° with an unprecedented resolution. As a result we were able to address some of the unknowns regarding the lithospheric structure beneath SW Iberia. The dispersion maps allow the imaging of the major structural units, namely the Iberian Massif, and the Lusitanian and Algarve Meso-Cenozoic basins. The Cadiz Gulf/Gibraltar Strait area corresponds to a strong low-velocity anomaly, which can be followed to the largest period inverted, although slightly shifted to the east at longer periods. Within the Iberian Massif, second-order perturbations in the group velocities are consistent with the transitions between tectonic units composing the massif. © 2013 Elsevier B.V.

Vales D.,Instituto Portugues do Mar e da Atmosfera IPMA | Dias N.A.,Polytechnic Institute of Lisbon | Dias N.A.,Instituto Dom Luiz IDL | Rio I.,Instituto Dom Luiz IDL | And 10 more authors.
Tectonophysics | Year: 2014

We present an analysis and characterization of the regional seismicity recorded by a temporary broadband seismic network deployed in the Cape Verde archipelago between November 2007 and September 2008.The detection of earthquakes was based on spectrograms, allowing the discrimination from low-frequency volcanic signals, resulting in 358 events of which 265 were located, the magnitudes usually being smaller than 3. For the location, a new 1-D P-velocity model was derived for the region showing a crust consistent with an oceanic crustal structure. The seismicity is located mostly offshore the westernmost and geologically youngest areas of the archipelago, near the islands of Santo Antão and São Vicente in the NW and Brava and Fogo in the SW. The SW cluster has a lower occurrence rate and corresponds to seismicity concentrated mainly along an alignment between Brava and the Cadamosto seamount presenting normal faulting mechanisms. The existence of the NW cluster, located offshore SW of Santo Antão, was so far unknown and concentrates around a recently recognized submarine cone field; this cluster presents focal depths extending from the crust to the upper mantle and suggests volcanic unrest. No evident temporal behaviour could be perceived, although the events tend to occur in bursts of activity lasting a few days. In this recording period, no significant activity was detected at Fogo volcano, the most active volcanic edifice in Cape Verde.The seismicity characteristics point mainly to a volcanic origin. The correlation of the recorded seismicity with active volcanic structures agrees with the tendency for a westward migration of volcanic activity in the archipelago as indicated by the geologic record. © 2014 Elsevier B.V.

Diaz J.,ICTJA CSIC | Gallart J.,ICTJA CSIC | Morais I.,Instituto Dom Luiz IDL | Silveira G.,Instituto Dom Luiz IDL | And 7 more authors.
Tectonophysics | Year: 2015

The knowledge of the anisotropic properties beneath the Iberian Peninsula and Northern Morocco has been dramatically improved since late 2007 with the analysis of the data provided by the dense TopoIberia broad-band seismic network, the increasing number of permanent stations operating in Morocco, Portugal and Spain, and the contribution of smaller scale/higher resolution experiments. Results from the two first TopoIberia deployments have evidenced a spectacular rotation of the fast polarization direction (FPD) along the Gibraltar Arc, interpreted as an evidence of mantle flow deflected around the high velocity slab beneath the Alboran Sea, and a rather uniform N100°E FPD beneath the central Iberian Variscan Massif, consistent with global mantle flow models taking into account contributions of surface plate motion, density variations and net lithosphere rotation. The results from the last Iberarray deployment presented here, covering the northern part of the Iberian Peninsula, also show a rather uniform FPD orientation close to N100°E, thus confirming the previous interpretation globally relating the anisotropic parameters to the LPO of mantle minerals generated by mantle flow at asthenospheric depths. However, the degree of anisotropy varies significantly, from delay time values of around 0.5 s beneath NW Iberia to values reaching 2.0 s in its NE corner. The anisotropic parameters retrieved from single events providing high quality data also show significant differences for stations located in the Variscan units of NW Iberia, suggesting that the region includes multiple anisotropic layers or complex anisotropy systems. These results allow to complete the map of the anisotropic properties of the westernmost Mediterranean region, which can now be considered as one of best constrained regions worldwide, with more than 300 sites investigated over an area extending from the Bay of Biscay to the Sahara platform. © 2015 Elsevier B.V.

Alcoforado M.J.,University of Lisbon | Vaquero J.M.,University of Extremadura | Vaquero J.M.,Instituto Dom Luiz IDL | Trigo R.M.,Instituto Dom Luiz IDL | And 2 more authors.
Climate of the Past | Year: 2012

Natural proxies, documentary evidence and instrumental data are the only sources used to reconstruct past climates. In this paper, we present the 18th century meteorologists (either Portuguese or foreigners) who made the first observations at several sites in Continental Portugal, Madeira Island and Rio de Janeiro (Brazil), from 1749 until 1802. Information is given concerning observation site, variables observed, measurement period, methods of measurements and sources (both manuscript and printed). Some examples from the data usefulness are given: rainfall variability in Madeira (1749-1753) and in continental Portugal (1781-1793) was reconstructed, allowing to extend towards the late 18th century the well known negative correlation between the NAO index and seasonal rainfall. Furthermore, previously unpublished data for 1783-1784 have allowed analysing the consequences of the Lakagígar eruption in Portugal: foggy and haze days are referred to in summer 1783, but unlike the hot summer observed in northern and central Europe, temperatures in Portugal were lower than average. Additionally, observations from Rio de Janeiro in Brazil show that the Lakagígar consequences may well have spread to sectors of the Southern Hemisphere. Although the series are short, the data have been used for climate reconstruction studies and may also be useful to improve the quality of large scale reconstruction datasets. © 2012 Author(s).

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