Évora, Portugal
Évora, Portugal

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Pereira S.N.,Evora Geophysics Center | Wagner F.,Evora Geophysics Center | Silva A.M.,Evora Geophysics Center | Silva A.M.,University of Évora
Atmospheric Chemistry and Physics | Year: 2011

Aerosol scattering properties, near the surface (at about 10m height), were measured during a period of seven years (2002-2008) at ́ Evora, Portugal. The average (and median) scattering and backscattering coefficients, at the wavelength of 550 nm, were found to be 42.5Mm-1 (29.9Mm-1) and 5.9Mm-1 (4.4Mm-1), respectively. Also, the average and median scattering Ångstr̈om exponent (1.4 and 1.5) indicate that scattering was, in general, dominated by submicrometer particles. Both seasonal and daily cycles are shown, which were related to local production and transport of particles from elsewhere. Summer and winter average values of the scattering coefficient, at the wavelength of 550 nm (47 and 54Mm-1, respectively), correspond to a significant increase in the aerosol particle concentration when compared with spring and fall (35 and 37Mm-1, respectively). Also, the average increase in the Ångstr̈om exponent for summer and winter seasons is consistent with the input of sub-micrometer particles from anthropogenic origin in winter and forest fires in summer. Back-trajectory analysis indicated that the site was regularly under the influence of air masses from the Atlantic area, with low particle loads (low scattering coefficients), but as the influence of transport from the continent (Iberia Peninsula) increased, the aerosol particle load was observed to increase as well as the relative importance of fine particles over coarse ones, approaching the features observed at the site during European air masses influence. © 2011 Author(s).

Silva C.,Polytechnic Institute of Tomar | Silva C.,Evora Geophysics Center | Reis A.H.,Evora Geophysics Center | Reis A.H.,University of Évora
International Journal of Thermal Sciences | Year: 2014

Apparently complex flow structures obey to scaling relations that enable to make it viable the study of their configuration and flow dynamics. This is the case of flow structures that exhibit several branching levels and are thought to perform optimally. Here we present scaling relations of diameters and lengths of branching cylindrical channels with pulsatile flows, and compare them with other relations published in the literature. It is shown that, under constant global volume of the flow tree, and for zero pulse frequency these scaling relations reduce to Murrays's law of consecutive diameters. Optimal scaling depends on pulse frequency, distensibility of the channel walls, and asymmetry of the daughter vessels. In case that in addition to global volume of the flow tree, the pressure head is also kept constant, a similar scaling law of channel lengths emerges that holds together with the law of diameter scaling. The effect of channel distensibility is shown to be somehow important, such that for achieving optimal performance (lowest impedance) channels with lower relative distensibility must have their diameter increased. Results are compared with those of other models for the case of some arteries. © 2014 Elsevier Masson SAS. All rights reserved.

Preissler J.,University of Évora | Preissler J.,Evora Geophysics Center | Wagner F.,University of Évora | Wagner F.,Evora Geophysics Center | And 5 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2011

An exceptionally strong outbreak of Saharan dust was observed in southern Portugal from 4 to 9 April 2011. The event was monitored with a multiwavelength Raman lidar, a CIMEL Sun photometer, the Cloud Aerosol Lidar with Orthogonal Polarization (CALIOP) and two Moderate Resolution Imaging Spectroradiometer (MODIS). Those instruments provided vertically resolved and columnar information about the optical properties of the mineral dust plume. Maximum aerosol optical depths in the free troposphere of 1.8 and 1.9 were observed with Raman lidar at 355 and 532nm, respectively. The mean extinction-related Ångström exponents (355, 532nm) from Raman lidar averaged over the whole period were 0.0 ± 0.2. Backscatter-related Ångström exponents (355, 532nm and 532, 1064nm) were 0.4 on average. Mean lidar ratios calculated from Raman lidar measurements were 45 ± 8sr at 355nm and 53 ± 7sr at 532nm. The mean linear particle depolarization ratio at 532nm was 0.28 ± 0.04. Furthermore, intrusion of Saharan dust into the planetary boundary layer could be observed with different ground-based in-situ instruments. Maximum particle mass concentration values (PM10) of 162 μg m-3 were detected at ground. The daily threshold of 50 μg m-3 for PM 10 was exceeded on three subsequent days during the considered period. The ratio of coarse to fine mode particle number concentration reached maximum values larger than 1, coinciding with the maximum in PM10 mass concentration. A comparison of ground-based Raman lidar measurements and CALIOP Level 2 data was done for one CALIPSO overpass. A good agreement was found for backscatter coefficients. Copyright 2011 by the American Geophysical Union.

Preibler J.,Evora Geophysics Center | Wagner F.,Evora Geophysics Center | Guerrero J.L.-R.,Evora Geophysics Center | Guerrero J.L.-R.,University of Granada | Silva A.M.,Evora Geophysics Center
Journal of Geophysical Research: Atmospheres | Year: 2013

Multi-wavelength Raman light detection and ranging (lidar) observations were analyzed, which were performed in Évora, Portugal, during more than 2 years on a regular basis in the framework of the European Aerosol Research Lidar Network (EARLINET). An aerosol characterization in terms of the lidar ratios at 355 and 532 nm and the extinction and backscatter related Ångström exponents is presented. Aerosol layers in the free troposphere were classified according to their origin. Clear differences in the intensive optical properties were found for layers of mineral dust from the Sahara and from Asia, of anthropogenic aerosol from Europe and from North America, as well as of biomass burning smoke from the Iberian Peninsula and from North America, respectively. In general, the mean Ångström exponents of aerosol layers of the same type, but from closer source regions, were smaller than those from aerosol layers transported over a longer distance. This hints at the deposition of large particles along the transportation path, especially for anthropogenic aerosol and mineral dust. Besides, the seasonal behavior of aerosol in the free troposphere over Évora was studied. Seventy-three percent of the detected layers were observed during spring and summer. On average, the layers were highest in summer with an overall mean layer height of (3.8?1.9) km above sea level (asl), and lowest in winter with (2.3?0.9) km asl. © 2013. American Geophysical Union. All Rights Reserved.

Couto F.T.,Evora Geophysics Center | Salgado R.,Evora Geophysics Center | Salgado R.,University of Évora | Costa M.J.,Evora Geophysics Center | Costa M.J.,University of Évora
Natural Hazards and Earth System Science | Year: 2012

This paper constitutes a step towards the understanding of some characteristics associated with high rainfall amounts and flooding on Madeira Island. The high precipitation events that occurred during the winter of 2009/2010 have been considered with three main goals: to analyze the main atmospheric characteristics associated with the events; to expand the understanding of the interaction between the island and the atmospheric circulations, mainly the effects of the island on the generation or intensification of orographic precipitation; and to evaluate the performance of high resolution numerical modeling in simulating and forecasting heavy precipitation events over the island. The MESO-NH model with a horizontal resolution of 1 km is used, as well as rain gauge data, synoptic charts and measurements of precipitable water obtained from the Atmospheric InfraRed Sounder (AIRS). The results confirm the influence of the orographic effects on precipitation over Madeira as well as the tropical–extratropical interaction, since atmospheric rivers were detected in six out of the seven cases analyzed, acting as a low level moisture supplier, which together with the orographic lifting induced the high rainfall amounts. Only in one of the cases the presence of a low pressure system was identified over the archipelago. © 2012 Author(s) 2012. CC Attribution 3.0 License.

Pereira S.N.,Evora Geophysics Center | Wagner F.,Evora Geophysics Center | Silva A.M.,Evora Geophysics Center | Silva A.M.,University of Évora
Atmospheric Environment | Year: 2012

Black carbon mass concentration (BCPM10) measurements carried out at évora, Portugal, between 2007 and 2009, were analyzed and interpreted at different timescales. Additional measurements of aerosol mass concentration (MPM10) were included and the black carbon to total mass fraction (BC mass fraction) was derived when measurements of both quantities were coincident. BCPM10 values were found to vary between 0.3 and 5 μg m -3, mainly in the range of 0.5-2 μg m -3. A clear and consistent seasonal behavior was found; an increase by a factor of two in the average BCPM10 values was observed from summer (0.9 μg m -3) to winter (1.8 μg m -3) which is reflected in the BC mass fraction, amplified from about 4 to 10%. Comparison of the average BCPM10 mass concentrations on week days and week ends indicate that local traffic emissions strongly influence the observed average diurnal patterns. Other factors, such as wood burning for heating, lower boundary layer height and more frequent winter-time temperature inversions, also likely influence the observed BCPM10 but were not directly studied here. When different air mass types are considered then black carbon levels show a much lower variation than PM 10 mass concentrations, stressing the relevance of local emissions in the BCPM10 levels. BCPM10 values under continental or maritime influence only differ by a factor of approximately 1.4 only, much lower than the factor of 10 reported for a coastal rural site in Portugal. © 2012 Elsevier Ltd.

Silva C.,Polytechnic Institute of Tomar | Silva C.,Evora Geophysics Center | Reis A.H.,Evora Geophysics Center | Reis A.H.,University of Évora
Journal of Biomechanics | Year: 2014

In this study we explore the ability of a previously developed model of pulsatile flow for explaining the observed reduction of arterial distensibility with heart rate. The parameters relevant for the analysis are arterial wall distensibility together with permeability and reflection coefficients of the end capillaries. A non-specific artery and the ensemble of tissues supplied by that artery were considered in the model. The blood current within that artery was equalized to the sum of all micro currents in the tissues supplied by that artery. A formula emerged that relates changes in arterial distensibility with heart rate, and also with some particular aspects of microcirculation. Then, that formula was tested with data of distensibilities of the radial and carotid arteries observed at the heart rates of 63, 90, and 110. b.p.m. The formula correctly predicted the trend of decreased distensibility with heart rate for both arteries. Moreover, due to the fact that the carotid artery supplies the brain, and because the Blood-Brain barrier is highly restrictive to colloids in the blood, for the carotid artery the formula predicted a less marked decrease in distensibility than in the case of the radial artery feeding muscle tissue, which has a greater permeability to colloids, a trend that was confirmed by data. It was found that reduction of arterial distensibility with heart rate was greater in arteries that supply end capillaries with high permeability and low reflection coefficients. © 2014 Elsevier Ltd.

Silva C.,Polytechnic Institute of Tomar | Silva C.,Evora Geophysics Center | Heitor Reis A.,Evora Geophysics Center | Heitor Reis A.,University of Évora
Medical Physics | Year: 2014

Purpose: The objectives are: (i) assess the development of the impedance of some arteries during the first decades of life; (ii) determine the influence of pulse rate in arterial impedance; (iii) compare the structure of some arterial segments with optimized structures with respect to blood flow; and (iv) explain the elongation of the ascending aorta throughout life in healthy subjects. Methods: A model of the arterial network previously developed by the authors, together with data of lengths, diameters, and distensibilities of arterial segments reported in the literature were used. The impedances of the aorta and carotid artery were calculated based on that model. Similarly, the impedances of various arteries corresponding to heart rates of 65 bpm and 120 bpm were calculated. Values observed in arterial segments were compared with the respective optimal values from the viewpoint of hemodynamic performance. This allowed drawing conclusions on the arterial segments that might be critical with regard to hemodynamics. Results: It was found that in healthy people impedances of the aorta and the carotid artery decrease markedly with age especially during body growth. It was also found that impedances of the main arteries do not significantly change with heart rate, even if sharp changes in arterial distensibility are observed. With respect to optimal flow performance, it was found that scaling between diameters of branching arteries is generally close to optimality, while the corresponding length scaling is far from optimality. It was also found that the ascending aorta and aortic arch are among those arterial segments whose lengths are much smaller than the optimum values. An explanation is offered for the age associated elongation of the aorta in healthy people. Conclusions: In healthy subjects, the human arterial system continues to optimize its performance at least until the age of 60. © 2014 American Association of Physicists in Medicine.

Nepomuceno Pereira S.,Evora Geophysics Center | Nepomuceno Pereira S.,Andalusian Institute for Earth System Research IISTA CEAMA | Wagner F.,Evora Geophysics Center | Wagner F.,Hohenpeissenberg Meteorological Observatory | Silva A.M.,Evora Geophysics Center
Advances in Meteorology | Year: 2014

Measurements of the aerosol absorption coefficient, between 2007 and 2013, were made at the ground level in Évora, a Portuguese small town located in the southwestern Iberia Peninsula. Such a relatively long time series of absorbing aerosols is unique in Portugal and uncommon elsewhere. The average aerosol absorption coefficient was close to 9 Mm-1 and clear cycles at both daily and seasonal time scales were found. An average increase by a factor of two (from 6 to 12 Mm-1) was observed in winter if compared to summer season. The daily variations were similarly shaped for all seasons, with two morning and afternoon peaks, but with magnitudes modulated by the seasonal evolution. That was not the case if Sundays were considered. These variations can be explained in terms of the impact of local particle sources, related mainly to traffic and biomass burning and upward mixing of the aerosol due to variable mixing layer heights, either daily or seasonally. Also, a strong negative correlation between the aerosol absorption coefficient and the wind speed was verified, and an exponential decay function was found to fit very well to the data. The wind direction seems to be not correlated with the aerosol absorption coefficient. © 2014 Sérgio Nepomuceno Pereira et al.

Obregon M.A.,University of Extremadura | Pereira S.,Evora Geophysics Center | Wagner F.,Evora Geophysics Center | Serrano A.,University of Extremadura | And 3 more authors.
Atmospheric Environment | Year: 2012

This study presents a characterization of aerosols columnar properties measured at three different AERONET sites in the western part of the Iberian Peninsula, namely évora and Cabo da Roca, in Portugal, and Cáceres, in Spain, during the period from 2005 to 2010. AERONET level 2.0 products have been analyzed. The comparison of these three stations has great interest because it has not been conducted yet and it allows to characterize the aerosols of a wide region in western Iberian Peninsula by a long-term analysis of their aerosol properties. In addition, it allows analyzing the possible differences in these properties between the three sites located at different distances from the coast. The results show differences between the aerosol optical depth at 440 and 1020 nm at the three stations, being the mean values in Cabo da Roca at 1020 and 440 nm (0.08 and 0.16) slightly higher than in the other two stations (évora: 0.06 and 0.15; Cáceres: 0.05 and 0.14). Greater differences among the three stations are found for the ångström exponent values. Thus, Cáceres shows the highest mean value (1.33), followed by évora (1.14) and, finally, by Cabo da Roca (1.00) which exhibits the smallest median α values due to the presence of coarse sea salt particles and high atmospheric humidity. These values are consistent with the values of volume size distribution, exhibiting a greater value of large particles at Cabo da Roca. The mean values of the single scattering albedo (ω) have been also analyzed, obtaining higher results as the coast is approached: Cabo da Roca: ω (440) = 0.95; ω (1020) = 0.96, évora: ω (440) = 0.93; ω (1020) = 0.95 and Cáceres: ω (440) = 0.88; ω (1020) = 0.83. The differences between the three stations are explained in terms of the distance to the coast and to the occasional arrival of diverse air masses transporting different aerosol types to each station. One classification method proposed for the study region has been applied to multi-year measurements performed at the three sites and verified by means of daily 120-h back-trajectory analyses of air masses. The most frequent situations observed at all sites include the clean, maritime and continental situations, which account for about 80% or more. The remaining percentage is accounted by the more episodic situations of desert dust (10-14%) and forest fires emissions (3-5%). The probability density plots calculated for the different classified aerosol situations show significant differences consistent with the different paths of the air masses corresponding to each aerosol situation. © 2012 Elsevier Ltd.

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