17 results on '"Samaras, Stefanos"'
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2. Modeling a Spheroidal Particle Ensemble and Inversion by Generalized Runge–Kutta Regularizers from Limited Data
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Samaras, Stefanos, primary, Böckmann, Christine, additional, and Ritter, Christoph, additional
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- 2022
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3. Lidar stand-alone retrieval of atmospheric aerosol microphysical properties during SLOPE
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Ortiz-Amezcua Pablo, Samaras Stefanos, Böckmann Christine, Antonio Benavent-Oltra Jose, Luis Guerrero-Rascado Juan, Román Roberto, and Alados-Arboledas Lucas
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Physics ,QC1-999 - Abstract
Two cases from SLOPE campaign at Granada are analyzed in terms of particle microphysical properties using novel software developed at Potsdam University. Multiwavelength Raman lidar measurements of particle extinction and backscatter coefficients as well as linear particle depolarization ratios are used as input for the software. The result of the retrieval is a 2-dimensional particle volume distribution as a function of radius and aspect ratio, from which the particle microphysical properties are obtained.
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- 2018
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4. Vertical Profiles of Aerosol Optical and Microphysical Properties During a Rare Case of Long-range Transport of Mixed Biomass Burning-polluted Dust Aerosols from the Russian Federation-kazakhstan to Athens, Greece
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Papayannis Alexandros, Argyrouli Athina, Kokkalis Panayotis, Tsaknakis Georgios, Binietoglou Ioannis, Solomos Stavros, Kazadzis Stylianos, Samaras Stefanos, Böckmann Christine, Raptis Panagiotis, and Amiridis Vassilis
- Subjects
Physics ,QC1-999 - Abstract
Multi-wavelength aerosol Raman lidar measurements with elastic depolarization at 532 nm were combined with sun photometry during the HYGRA-CD campaign over Athens, Greece, on May-June 2014. We retrieved the aerosol optical [3 aerosol backscatter profiles (baer) at 355-532-1064 nm, 2 aerosol extinction (aaer) profiles at 355-532 nm and the aerosol linear depolarization ratio (δ) at 532 nm] and microphysical properties [effective radius (reff), complex refractive index (m), single scattering albedo (ω)]. We present a case study of a long distance transport (~3.500-4.000 km) of biomass burning particles mixed with dust from the Russian Federation-Kazakhstan regions arriving over Athens on 21-23 May 2014 (1.7-3.5 km height). On 23 May, between 2-2.75 km we measured mean lidar ratios (LR) of 35 sr (355 nm) and 42 sr (532 nm), while the mean Ångström exponent (AE) aerosol backscatter-related values (355nm/532nm and 532nm/1064nm) were 2.05 and 1.22, respectively; the mean value of δ at 532 nm was measured to be 9%. For that day the retrieved mean aerosol microphysical properties at 2-2.75 km height were: reff=0.26 μm (fine mode), reff=2.15 μm (coarse mode), m=1.36+0.00024i, ω=0.999 (355 nm, fine mode), ω=0.992(355 nm, coarse mode), ω=0.997 (532 nm, fine mode), and ω=0.980 (532 nm, coarse mode).
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- 2016
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5. Combined sphere-spheroid particle model for the retrieval of the microphysical aerosol parameters via regularized inversion of lidar data
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Samaras Stefanos, Böckmann Christine, and Nicolae Doina
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Physics ,QC1-999 - Abstract
In this work we propose a two-step advancement of the Mie spherical-particle model accounting for particle non-sphericity. First, a naturally two-dimensional (2D) generalized model (GM) is made, which further triggers analogous 2D re-definitions of microphysical parameters. We consider a spheroidal-particle approach where the size distribution is additionally dependent on aspect ratio. Second, we incorporate the notion of a sphere-spheroid particle mixture (PM) weighted by a non-sphericity percentage. The efficiency of these two models is investigated running synthetic data retrievals with two different regularization methods to account for the inherent instability of the inversion procedure. Our preliminary studies show that a retrieval with the PM model improves the fitting errors and the microphysical parameter retrieval and it has at least the same efficiency as the GM. While the general trend of the initial size distributions is captured in our numerical experiments, the reconstructions are subject to artifacts. Finally, our approach is applied to a measurement case yielding acceptable results.
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- 2016
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6. EARLINET observations of Saharan dust intrusions over the northern Mediterranean region (2014–2017): properties and impact on radiative forcing
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Soupiona, Ourania, primary, Papayannis, Alexandros, additional, Kokkalis, Panagiotis, additional, Foskinis, Romanos, additional, Sánchez Hernández, Guadalupe, additional, Ortiz-Amezcua, Pablo, additional, Mylonaki, Maria, additional, Papanikolaou, Christina-Anna, additional, Papagiannopoulos, Nikolaos, additional, Samaras, Stefanos, additional, Groß, Silke, additional, Mamouri, Rodanthi-Elisavet, additional, Alados-Arboledas, Lucas, additional, Amodeo, Aldo, additional, and Psiloglou, Basil, additional
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- 2020
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7. Saharan dust intrusions over the northern Mediterranean region in the frame of EARLINET (2014–2017): Properties and impact in radiative forcing
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Soupiona, Ourania, primary, Papayannis, Alexandros, additional, Kokkalis, Panagiotis, additional, Foskinis, Romanos, additional, Sánchez Hernández, Guadalupe, additional, Ortiz-Amezcua, Pablo, additional, Mylonaki, Maria, additional, Papanikolaou, Christina-Anna, additional, Papagiannopoulos, Nikolaos, additional, Samaras, Stefanos, additional, Groß, Silke, additional, Mamouri, Rodanthi-Elisavet, additional, Alados-Arboledas, Lucas, additional, Amodeo, Aldo, additional, and Psiloglou, Basil, additional
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- 2020
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8. Retrieval of microphysical dust particle properties from SALTRACE lidar observations: Case studies
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Samaras, Stefanos, primary, Böckmann, Christine, additional, Haarig, Moritz, additional, Ansmann, Albert, additional, Walser, Adrian, additional, and Weinzierl, Bernadett, additional
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- 2020
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9. A probabilistic approach for the retrieval of mineral dust properties from infrared spaceborne observations
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Samaras, Stefanos, primary and Popp, Thomas, additional
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- 2020
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10. Microphysical characterization of smoke from Canadian fires
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Gialitaki, Anna G., Tsekeri, Alexandra, Vassilis Amiridis, Samaras, Stefanos, Marinou, Eleni, Haarig, Moritz, Baars, Holger, Tetoni, Eleni, and Ansmann, Albert
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- 2018
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11. Saharan dust intrusions over the northern Mediterranean region in the frame of EARLINET (2014-2017): Properties and impact in radiative forcing.
- Author
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Soupiona, Ourania, Papayannis, Alexandros, Kokkalis, Panagiotis, Foskinis, Romanos, Hernández, Guadalupe Sánchez, Ortiz-Amezcua, Pablo, Mylonaki, Maria, Papanikolaou, Christina-Anna, Papagiannopoulos, Nikolaos, Samaras, Stefanos, Groß, Silke, Mamouri, Rodanthi-Elisavet, Alados-Arboledas, Lucas, Amodeo, Aldo, and Psiloglou, Basil
- Abstract
Remote sensing measurements of aerosols using depolarization Raman Lidar systems from 4 EARLINET (European Aerosol research Lidar Network) stations are used for a comprehensive analysis of Saharan dust events over the Mediterranean basin in the period 2014-2017. In this period, we selected to study 51 dust events regarding the geometrical, optical and microphysical properties of dust particles, classifying them and assessing their radiative forcing effect on the atmosphere. From West to East, the stations of Granada, Potenza, Athens and Limassol were selected as representative Mediterranean cities regularly affected by Saharan dust intrusions. Emphasis was given on lidar measurements in the visible (532 nm) and specifically on the consistency of the particle linear depolarization ratio (d
p532 ), the extinction-to-backscatter lidar ratio (LR532 ) and the Aerosol Optical Thickness (AOT532 ) within the observed dust layers. We found mean dp532 values of 0.24 ± 0.05, 0.26 ± 0.06, 0.28 ± 0.05 and 0.28 ± 0.04, mean LR532 values of 52 ± 8 sr, 51 ± 9 sr, 52 ± 9 sr and 49 ± 6 sr, and mean AOT532 values of 0.40 ± 0.31, 0.11 ± 0.07, 0.12 ± 0.10 and 0.32 ± 0.17, for Granada, Potenza, Athens and Limassol, respectively. The mean layer thickness values were found to range from ~1700 to ~3400 m. Additionally, based also on a previous aerosol type classification scheme provided by airborne High Spectral Resolution Lidar (HSRL) observations and on air mass backward trajectory analysis, a clustering analysis was performed in order to identify the major mixing aerosol types over the studied area. Furthermore, a synergy of lidar measurements and modeling was used to deeply analyze the solar and thermal radiative forcing of airborne dust. In total, a cooling behavior in the solar range and a significantly lower heating behavior in the thermal range was estimated. Depending on the dust optical and geometrical properties, the load intensity and the solar zenith angle (SZA), the estimated solar radiative forcing values range from -59 to -22 W m-2 at the surface and from -24 to -1 W m-2 at the top of the atmosphere (TOA). Similarly, in the thermal spectral range these values range from +2 to +4 W m-2 for the surface and from +1 to +3 W m-2 for the TOA. Finally, the radiative forcing seems to be inversely proportional to the dust mixing ratio, since higher absolute values are estimated for less mixed dust layers. [ABSTRACT FROM AUTHOR]- Published
- 2020
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12. Retrieval of microphysical dust particle properties from SALTRACE lidar observations: Case studies.
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Samaras, Stefanos, Böckmann, Christine, Haarig, Moritz, Ansmann, Albert, Walser, Adrian, and Weinzierl, Bernadett
- Abstract
Saharan dust is a major natural atmospheric aerosol component with significant impact on the Earth radiation budget. In this work we determine the microphysical properties of dust particles after a long-range transport over the Atlantic Ocean, using input from three depolarization channels of a multi-wavelength polarization Raman lidar. The measurements were performed at Barbados in the framework of the Saharan Aerosol Long-Range Transport and Aerosol-Cloud-Interaction Experiment (SALTRACE) in the summers of 2013 and 2014. The microphysical retrievals are performed with the software tool SphInX (Spheroidal Inversion Experiments) which uses regularization for the inversion process and a new two-dimensional (2-D) extension of the Mie model approximating dust with spheroids. The method allows us to simultaneously retrieve shape- and size-dependent particle distributions. Because dust particles are mostly non-spherical this software tool fills the gap in estimating the non-spherical particle fraction. Two cases measured on 10 July 2013 and 20 June 2014 are discussed. 2-D radius-bimodal shape-size distribution are retrieved. The ratio of spherical-to-non-spherical contributions to the particle number concentration was found to be about 3/7. A volume-weighted effective aspect ratio of 1.1 was obtained, indicating slightly prolate particles. The total effective radius for the two cases in the preselected radius range from 0.01-2.2 μm was found to be, on average, 0.75 μm. The stronger dust event (10 July 2013) showed about 24 % higher values for the total surface-area and volume concentration. Finally, we compare our results with the ones from the polarization lidar-photometer networking (POLIPHON) method and ground-based photometers as well as with airborne in situ particle counters. Considering all differences in these independent approaches, we find a qualitatively good agreement between the different results and a consistent description of the dust cases. Such an extensive comparison is a novel and fruitful exercise and corroborates that the mathematical retrieval based on Raman lidar data of particle backscattering, extinction, and depolarization is a powerful tool even in the case of dust particles. [ABSTRACT FROM AUTHOR]
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- 2020
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13. Retrieval der Mikrophysik von nichtkugelförmigen Aerosolpartikeln durch regularisierte Inversion von Mehrwellenlängen-Lidardaten
- Author
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Samaras, Stefanos
- Subjects
Institut für Mathematik ,ddc:510 - Abstract
Numerous reports of relatively rapid climate changes over the past century make a clear case of the impact of aerosols and clouds, identified as sources of largest uncertainty in climate projections. Earth’s radiation balance is altered by aerosols depending on their size, morphology and chemical composition. Competing effects in the atmosphere can be further studied by investigating the evolution of aerosol microphysical properties, which are the focus of the present work. The aerosol size distribution, the refractive index, and the single scattering albedo are commonly used such properties linked to aerosol type, and radiative forcing. Highly advanced lidars (light detection and ranging) have reduced aerosol monitoring and optical profiling into a routine process. Lidar data have been widely used to retrieve the size distribution through the inversion of the so-called Lorenz-Mie model (LMM). This model offers a reasonable treatment for spherically approximated particles, it no longer provides, though, a viable description for other naturally occurring arbitrarily shaped particles, such as dust particles. On the other hand, non-spherical geometries as simple as spheroids reproduce certain optical properties with enhanced accuracy. Motivated by this, we adapt the LMM to accommodate the spheroid-particle approximation introducing the notion of a two-dimensional (2D) shape-size distribution. Inverting only a few optical data points to retrieve the shape-size distribution is classified as a non-linear ill-posed problem. A brief mathematical analysis is presented which reveals the inherent tendency towards highly oscillatory solutions, explores the available options for a generalized solution through regularization methods and quantifies the ill-posedness. The latter will improve our understanding on the main cause fomenting instability in the produced solution spaces. The new approach facilitates the exploitation of additional lidar data points from depolarization measurements, associated with particle non-sphericity. However, the generalization of LMM vastly increases the complexity of the problem. The underlying theory for the calculation of the involved optical cross sections (T-matrix theory) is computationally so costly, that would limit a retrieval analysis to an unpractical point. Moreover the discretization of the model equation by a 2D collocation method, proposed in this work, involves double integrations which are further time consuming. We overcome these difficulties by using precalculated databases and a sophisticated retrieval software (SphInX: Spheroidal Inversion eXperiments) especially developed for our purposes, capable of performing multiple-dataset inversions and producing a wide range of microphysical retrieval outputs. Hybrid regularization in conjunction with minimization processes is used as a basis for our algorithms. Synthetic data retrievals are performed simulating various atmospheric scenarios in order to test the efficiency of different regularization methods. The gap in contemporary literature in providing full sets of uncertainties in a wide variety of numerical instances is of major concern here. For this, the most appropriate methods are identified through a thorough analysis on an overall-behavior basis regarding accuracy and stability. The general trend of the initial size distributions is captured in our numerical experiments and the reconstruction quality depends on data error level. Moreover, the need for more or less depolarization points is explored for the first time from the point of view of the microphysical retrieval. Finally, our approach is tested in various measurement cases giving further insight for future algorithm improvements. Zahlreiche Berichte von relativ schnellen Klimaveränderungen im vergangenen Jahrhundert liefern überzeugende Argumente über die Auswirkungen von Aerosolen und Wolken auf Wetter und Klima. Aerosole und Wolken wurden als Quellen größter Unsicherheit in Klimaprognosen identifiziert. Die Strahlungsbilanz der Erde wird verändert durch die Partikelgröße, ihre Morphologie und ihre chemische Zusammensetzung. Konkurrierende Effekte in der Atmosphäre können durch die Bestimmung von mikrophysikalischen Partikeleigenschaften weiter untersucht werden, was der Fokus der vorliegenden Arbeit ist. Die Aerosolgrößenverteilung, der Brechungsindex der Partikeln und die Einzel-Streu-Albedo sind solche häufig verwendeten Parameter, die mit dem Aerosoltyp und dem Strahlungsantrieb verbunden sind. Hoch entwickelte Lidare (Light Detection and Ranging) haben die Aerosolüberwachung und die optische Profilierung zu einem Routineprozess gemacht. Lidar-Daten wurden verwendet um die Größenverteilung zu bestimmen, was durch die Inversion des sogenannten Lorenz-Mie-Modells (LMM) gelingt. Dieses Modell bietet eine angemessene Behandlung für sphärisch angenäherte Partikeln, es stellt aber keine brauchbare Beschreibung für andere natürlich auftretende beliebig geformte Partikeln -wie z.B. Staubpartikeln- bereit. Andererseits stellt die Einbeziehung einer nicht kugelförmigen Geometrie –wie z.B. einfache Sphäroide- bestimmte optische Eigenschaften mit verbesserter Genauigkeit dar. Angesichts dieser Tatsache erweitern wir das LMM durch die Approximation von Sphäroid-Partikeln. Dazu ist es notwendig den Begriff einer zweidimensionalen Größenverteilung einzuführen. Die Inversion einer sehr geringen Anzahl optischer Datenpunkte zur Bestimmung der Form der Größenverteilung ist als ein nichtlineares schlecht gestelltes Problem bekannt. Eine kurze mathematische Analyse wird vorgestellt, die die inhärente Tendenz zu stark oszillierenden Lösungen zeigt. Weiterhin werden Optionen für eine verallgemeinerte Lösung durch Regularisierungsmethoden untersucht und der Grad der Schlechtgestelltheit quantifiziert. Letzteres wird unser Verständnis für die Hauptursache der Instabilität bei den berechneten Lösungsräumen verbessern. Der neue Ansatz ermöglicht es uns, zusätzliche Lidar-Datenpunkte aus Depolarisationsmessungen zu nutzen, die sich aus der Nicht-sphärizität der Partikeln assoziieren. Die Verallgemeinerung des LMMs erhöht erheblich die Komplexität des Problems. Die zugrundeliegende Theorie für die Berechnung der beteiligten optischen Querschnitte (T-Matrix-Ansatz) ist rechnerisch so aufwendig, dass eine Neuberechnung dieser nicht sinnvoll erscheint. Darüber hinaus wird ein zweidimensionales Kollokationsverfahren für die Diskretisierung der Modellgleichung vorgeschlagen. Dieses Verfahren beinhaltet Doppelintegrationen, die wiederum zeitaufwendig sind. Wir überwinden diese Schwierigkeiten durch Verwendung vorgerechneter Datenbanken sowie einer hochentwickelten Retrieval-Software (SphInX: Spheroidal Inversion eXperiments). Diese Software wurde speziell für unseren Zweck entwickelt und ist in der Lage mehrere Datensatzinversionen gleichzeitig durchzuführen und eine große Auswahl von mikrophysikalischen Retrieval-Ausgaben bereitzustellen. Eine hybride Regularisierung in Verbindung mit einem Minimierungsverfahren wird als Grundlage für unsere Algorithmen verwendet. Synthetische Daten-Inversionen werden mit verschiedenen atmosphärischen Szenarien durchgeführt, um die Effizienz verschiedener Regularisierungsmethoden zu untersuchen. Die Lücke in der gegenwärtigen wissenschaftlichen Literatur gewisse Unsicherheiten durch breitgefächerte numerische Fälle bereitzustellen, ist ein Hauptanliegen dieser Arbeit. Motiviert davon werden die am besten geeigneten Verfahren einer gründlichen Analyse in Bezug auf ihr Gesamtverhalten, d.h. Genauigkeit und Stabilität, unterzogen. Der allgemeine Trend der Anfangsgrößenverteilung wird in unseren numerischen Experimenten erfasst. Zusätzlich hängt die Rekonstruktionsqualität vom Datenfehler ab. Darüber hinaus wird die Anzahl der notwendigen Depolarisationspunkte zum ersten Mal aus der Sicht des mikrophysikalischen Parameter-Retrievals erforscht. Abschließend verwenden wir unsere Software für verschiedene Messfälle, was weitere Einblicke für künftige Verbesserungen des Algorithmus gibt.
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- 2016
14. Microphysical characterization of long-range transported biomass burning particles from North America at three EARLINET stations
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Ortiz-Amezcua, Pablo, primary, Guerrero-Rascado, Juan Luis, additional, Granados-Muñoz, María José, additional, Benavent-Oltra, José Antonio, additional, Böckmann, Christine, additional, Samaras, Stefanos, additional, Stachlewska, Iwona S., additional, Janicka, Łucja, additional, Baars, Holger, additional, Bohlmann, Stephanie, additional, and Alados-Arboledas, Lucas, additional
- Published
- 2017
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15. Microphysical characterization of long-range transported biomass burning particles from North America at three EARLINET stations
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Ortiz-Amezcua, Pablo, primary, Guerrero-Rascado, Juan Luis, additional, Granados-Muñoz, María José, additional, Benavent-Oltra, José Antonio, additional, Böckmann, Christine, additional, Samaras, Stefanos, additional, Stachlewska, Iwona S., additional, Janicka, Łucja, additional, Baars, Holger, additional, Bohlmann, Stephanie, additional, and Alados-Arboledas, Lucas, additional
- Published
- 2016
- Full Text
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16. Microphysical characterization of long-range transported biomass burning particles from North America at three EARLINET stations.
- Author
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Ortiz-Amezcua, Pablo, Guerrero-Rascado, Juan Luis, Granados-Muñoz, María José, Benavent-Oltra, José Antonio, Böckmann, Christine, Samaras, Stefanos, Stachlewska, Iwona S., Janicka, Łucja, Baars, Holger, Bohlmann, Stephanie, and Alados-Arboledas, Lucas
- Abstract
Strong events of long-range transported biomass burning aerosol were detected during July 2013 at three EARLINET stations, namely Granada (Spain), Leipzig (Germany) and Warsaw (Poland). Satellite observations from MODIS and CALIOP instruments, as well as modeling tools such as HYSPLIT and NAAPS have been used to estimate the sources and transport paths of those North American forest fire smoke particles. Multiwavelength Raman lidar technique was applied to obtain vertically-resolved particle optical properties, and further inversion of those properties with regularization algorithm allowed for retrieving microphysical information on the studied particles. The results highlight the presence of smoke layers of 1-2 km thickness, located at about 5 km asl altitude over Granada and Leipzig, and around 2.5 km asl at Warsaw. These layers were intense, as they accounted for more than 30% of the total AOD in all cases, and presented optical and microphysical features typical for different aging degrees: color ratio of lidar ratios (LR532/LR355) around 2, α-related Angström exponents of less than 1, effective radii of 0.3 μm, and large values of single scattering albedos, nearly spectrally independent. The intensive microphysical properties were compared with columnar retrievals form co-located AERONET stations. The intensity of the layers was also characterized in terms of particle volume concentration, and then an experimental relationship between this magnitude and the particle extinction coefficient was established. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
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17. Microphysical characterization of long-range transported biomass burning particles from North America at three EARLINET stations
- Author
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Ortiz-Amezcua, Pablo, Guerrero-Rascado, Juan Luis, Granados-Muñoz, María José, Benavent-Oltra, José Antonio, Böckmann, Christine, Samaras, Stefanos, Stachlewska, Iwona S., Janicka, Łucja, Baars, Holger, Bohlmann, Stephanie, and Alados-Arboledas, Lucas
- Subjects
13. Climate action ,550 Geowissenschaften - Abstract
Strong events of long-range transported biomass burning aerosol were detected during July 2013 at three EARLINET (European Aerosol Research Lidar Network) stations, namely Granada (Spain), Leipzig (Germany) and Warsaw (Poland). Satellite observations from MODIS (Moderate Resolution Imaging Spectroradiometer) and CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) instruments, as well as modeling tools such as HYSPLIT (Hybrid Single-Particle Lagrangian Integrated Trajectory) and NAAPS (Navy Aerosol Analysis and Prediction System), have been used to estimate the sources and transport paths of those North American forest fire smoke particles. A multiwavelength Raman lidar technique was applied to obtain vertically resolved particle optical properties, and further inversion of those properties with a regularization algorithm allowed for retrieving microphysical information on the studied particles. The results highlight the presence of smoke layers of 1-2 km thickness, located at about 5 km a.s.l. altitude over Granada and Leipzig and around 2.5 km a.s.l. at Warsaw. These layers were intense, as they accounted for more than 30% of the total AOD (aerosol optical depth) in all cases, and presented optical and microphysical features typical for different aging degrees: color ratio of lidar ratios (LR532/LR355) around 2, alpha-related angstrom exponents of less than 1, effective radii of 0.3 mu m and large values of single scattering albedos (SSA), nearly spectrally independent. The intensive microphysical properties were compared with columnar retrievals form co-located AERONET (Aerosol Robotic Network) stations. The intensity of the layers was also characterized in terms of particle volume concentration, and then an experimental relationship between this magnitude and the particle extinction coefficient was established., Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe, 614
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