Dynamic Response of Face Symmetrical Hardfill Dams (FSHD)

94 σ.Αναλύεται η δυναμική συμπεριφόρα ένος σχετικά νέου είδους φράγματος, του (κακώς) ονομαζόμενου «Αξονοσυμμετρικού» Φράγματος Σκληρού Επιχώματος, δηλαδή ενός επιχώματος με ίδιες κλίσεις στα δύο πρανή. Αρχικά εξηγούμε τα χαρακτηριστικά αυτού του φράγματος και έπειτα παρουσιάζουμε το θεωρητικό υπόβαθρο για να επαληθεύσουμε τα αποτελέσματα της ανάλυσης. Τέλος δείχνουμε τα αποτελέσματα των αναλύσεων που έγιναν με πεπερασμένα στοιχεία. Το κύριο συμπέρασμα είναι ότι ακόμη και με υπό μετρίως ισχυρή σεισμική διέγερση οι αναπτυσσόμενες επιταχύνσεις στην κορυφή του φράγματος είναι πολύ μεγάλες, με αποτέλεσμα η δημιουργία επικίνδυνων εφελκυστικών ρωγμών να είναι αναπόφευκτη.Analyze the dynamic behavior of a relatively new type of dam, the (wrong) so-called "axisymmetric" Hardfill dam, ie a hardfill dam with the same slopes. FIrstly we explain the characteristics of this dam and then we present the theoretical background to verify the assay results. Finally we show the results of the analyses which were made by finite elements. The main conclusion is that even under moderately strong earthquake motions, the developing seismic accelerations at the top of the dam is very large, resulting in dangerous tensile cracks to be unavoidable.Αριστείδης Κ. Κουρτίδη

Spatiotemporal Variability and Contribution of Different Aerosol Types to the Aerosol Optical Depth over the Eastern Mediterranean

This study characterizes the spatiotemporal variability and relative contribution of different types of aerosols to the aerosol optical depth (AOD) over the Eastern Mediterranean as derived from MODIS (Moderate Resolution Imaging Spectroradiometer) Terra (March 2000-December 2012) and Aqua (July 2002-December 2012) satellite instruments. For this purpose, a 0.1deg 0.1deg gridded MODIS dataset was compiled and validated against sun photometric observations from the AErosol RObotic NETwork (AERONET). The high spatial resolution and long temporal coverage of the dataset allows for the determination of local hot spots like megacities, medium-sized cities, industrial zones and power plant complexes, seasonal variabilities and decadal averages. The average AOD at 550 nm (AOD550) for the entire region is approx. 0.22 +/- 0.19, with maximum values in summer and seasonal variabilities that can be attributed to precipitation, photochemical production of secondary organic aerosols, transport of pollution and smoke from biomass burning in central and eastern Europe and transport of dust from the Sahara and the Middle East. The MODIS data were analyzed together with data from other satellite sensors, reanalysis projects and a chemistry-aerosol-transport model using an optimized algorithm tailored for the region and capable of estimating the contribution of different aerosol types to the total AOD550. The spatial and temporal variability of anthropogenic, dust and fine-mode natural aerosols over land and anthropogenic, dust and marine aerosols over the sea is examined. The relative contribution of the different aerosol types to the total AOD550 exhibits a low/high seasonal variability over land/sea areas, respectively. Overall, anthropogenic aerosols, dust and fine-mode natural aerosols account for approx. 51, approx. 34 and approx. 15 % of the total AOD550 over land, while, anthropogenic aerosols, dust and marine aerosols account approx. 40, approx. 34 and approx. 26 % of the total AOD550 over the sea, based on MODIS Terra and Aqua observations

A 3-D evaluation of the MACC reanalysis dust product over Europe, northern Africa and Middle East using CALIOP/CALIPSO dust satellite observations

The MACC reanalysis dust product is evaluated over Europe, northern Africa and the Middle East using the EARLINET-optimized CALIOP/CALIPSO pure dust satellite-based product LIVAS (2007–2012). MACC dust optical depth at 550nm (DOD550) data are compared against LIVAS DOD532 observations. As only natural aerosol (dust and sea salt) profiles are available in MACC, here we focus on layers above 1kma.s.l. to diminish the influence of sea salt particles that typically reside at low heights. So, MACC natural aerosol extinction coefficient profiles at 550nm are compared against dust extinction coefficient profiles at 532nm from LIVAS, assuming that the MACC natural aerosol profile data can be similar to the dust profile data, especially over pure continental regions. It is shown that the reanalysis data are capable of capturing the major dust hot spots in the area as the MACC DOD550 patterns are close to the LIVAS DOD532 patterns throughout the year. MACC overestimates DOD for regions with low dust loadings and underestimates DOD for regions with high dust loadings where DOD exceeds  ∼ 0.3. The mean bias between the MACC and LIVAS DOD is 0.025 ( ∼ 25%) over the whole domain. Both MACC and LIVAS capture the summer and spring high dust loadings, especially over northern Africa and the Middle East, and exhibit similar monthly structures despite the biases. In this study, dust extinction coefficient patterns are reported at four layers (layer 1: 1200–3000ma.s.l., layer 2: 3000–4800ma.s.l., layer 3: 4800–6600m a.s.l. and layer 4: 6600–8400ma.s.l.). The MACC and LIVAS extinction coefficient patterns are similar over areas characterized by high dust loadings for the first three layers. Within layer 4, MACC overestimates extinction coefficients consistently throughout the year over the whole domain. MACC overestimates extinction coefficients compared to LIVAS over regions away from the major dust sources while over regions close to the dust sources (the Sahara and Middle East) it underestimates strongly only for heights below  ∼ 3–5kma.s.l. depending on the period of the year. In general, it is shown that dust loadings appear over remote regions and at heights up to 9kma.s.l. in MACC contrary to LIVAS. This could be due to the model performance and parameterizations of emissions and other processes, due to the assimilation of satellite aerosol measurements over dark surfaces only or due to a possible enhancement of aerosols by the MACC assimilation system

Nine-year spatial and temporal evolution of desert dust aerosols over South and East Asia as revealed by CALIOP

We present a 3-D climatology of the desert dust distribution over South and East Asia derived using CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation) data. To distinguish desert dust from total aerosol load we apply a methodology developed in the framework of EARLINET (European Aerosol Research Lidar Network). The method involves the use of the particle linear depolarization ratio and updated lidar ratio values suitable for Asian dust, applied to multiyear CALIPSO observations (January 2007-December 2015). The resulting dust product provides information on the horizontal and vertical distribution of dust aerosols over South and East Asia along with the seasonal transition of dust transport pathways. Persistent high D_AOD (dust aerosol optical depth) values at 532 nm, of the order of 0.6, are present over the arid and semi-arid desert regions. Dust aerosol transport (range, height and intensity) is subject to high seasonality, with the highest values observed during spring for northern China (Taklimakan and Gobi deserts) and during summer over the Indian subcontinent (Thar Desert). Additionally, we decompose the CALIPSO AOD (aerosol optical depth) into dust and non-dust aerosol components to reveal the non-dust AOD over the highly industrialized and densely populated regions of South and East Asia, where the non-dust aerosols yield AOD values of the order of 0.5. Furthermore, the CALIPSO-based short-term AOD and D_AOD time series and trends between January 2007 and December 2015 are calculated over South and East Asia and over selected subregions. Positive trends are observed over northwest and east China and the Indian subcontinent, whereas over southeast China trends are mostly negative. The calculated AOD trends agree well with the trends derived from Aqua MODIS (Moderate Resolution Imaging Spectroradiometer), although significant differences are observed over specific regions.Peer reviewe

hackAIR: Towards Raising Awareness about Air Quality in Europe by Developing a Collective Online Platform

Although air pollution is one of the most significant environmental factors posing a threat to human health worldwide, air quality data are scarce or not easily accessible in most European countries. The current work aims to develop a centralized air quality data hub that enables citizens to contribute to air quality monitoring. In this work, data from official air quality monitoring stations are combined with air pollution estimates from sky-depicting photos and from low-cost sensing devices that citizens build on their own so that citizens receive improved information about the quality of the air they breathe. Additionally, a data fusion algorithm merges air quality information from various sources to provide information in areas where no air quality measurements exist

Natural Aerosols, Gaseous Precursors and Their Impacts in Greece: A Review from the Remote Sensing Perspective

The Mediterranean, and particularly its Eastern basin, is a crossroad of air masses advected from Europe, Asia and Africa. Anthropogenic emissions from its megacities meet over the Eastern Mediterranean, with natural emissions from the Saharan and Middle East deserts, smoke from frequent forest fires, background marine and pollen particles emitted from ocean and vegetation, respectively. This mixture of natural aerosols and gaseous precursors (Short-Lived Climate Forcers—SLCFs in IPCC has short atmospheric residence times but strongly affects radiation and cloud formation, contributing the largest uncertainty to estimates and interpretations of the changing cloud and precipitation patterns across the basin. The SLCFs’ global forcing is comparable in magnitude to that of the long-lived greenhouse gases; however, the local forcing by SLCFs can far exceed those of the long-lived gases, according to the Intergovernmental Panel on Climate Change (IPCC). Monitoring the spatiotemporal distribution of SLCFs using remote sensing techniques is important for understanding their properties along with aging processes and impacts on radiation, clouds, weather and climate. This article reviews the current state of scientific know-how on the properties and trends of SLCFs in the Eastern Mediterranean along with their regional interactions and impacts, depicted by ground- and space-based remote sensing techniques