bluuebunny/crossref_metadata_2025 huggingface dataset:
Statistical methods of images analysis as an essential tool in the assessment process of computer methods intended for numerical simulations of cavitating flows
Authors: Niedźwiedzka Agnieszka , Lipiński Seweryn
Published: September 2017

Cavitation,  because  of  its  negative  effects,  like  e.g.  erosion,  noise  or  vibration,  is  usually  an  undesirablephenomenon. However, in devices where spraying and atomization are expected, cavitation is required. This group of devices includes e.g. diesel injectors. Appearance of vapour bubbles results in increase of the maximum flow velocity. It is possible for the following reasons. Firstly, bubbles start to form in the throat, so its diameter reduces. Secondly, appearance of vapour bubbles along the wall results in a slip boundary condition. Moreover, cavitation has a positive influence on a spray cone angle. However, regardless of the place of occurrence, research on cavitation bases primarily on numerical simulations. The area of numerical methods intended for cavitating flows includes many solutions which differ not only in the basic assumptions, i.e. considering flow either as a multiphase mixture with the average density or just as two independent liquids, fluid and vapour, with a distinct boundary between them, but also in many methods applied in particular approaches. Currently, to choose the best way of the prediction of cavitation phenomenon for the undertaken issue, many aspects should be considered. The most important factor is the assessment level between the results of numerical simulation and experimental data. Secondary are computing time, requirements for the hardware, price of software and additional costs connected with the selected software. The final decision about the chosen way of the cavitation prediction results from all the above-considered elements. The main aim of the work is to present the methods of image analysis, which can be very helpful in this process. The main advantage of these methods is the quantitative answer about the correlation degree between analysed images. It eliminates subjective decisions based solely on a raw imaging material. The image material used in the work was obtained via numerical simulations performed in ANSYS Fluent. Presented methodology bases on their statistical analysis that considers the shape and intensity of cavitating area, as well as on basic methods of image processing and analysis. The conclusion is that the obtained results demonstrate the usefulness of the proposed methods in the aspect of a reliable comparison of images obtained in the numericalstudies of the cavitation phenomenon.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4993
Internal flow and air core dynamics in simplex and spill-return pressure-swirl atomizers
Authors: Maly Milan , Janáčková Lada , Jedelský Jan , Sláma Jaroslav , Sapík Marcel , Wigley Graham
Published: September 2017

It is well known that the spray characteristics of pressure-swirl atomizers are strongly linked to the internal flow andthat an unstable air core may cause instabilities in the spray. In this paper, a 10:1 scale transparent Plexiglas (PMMA) model of a pressure-swirl atomizer as used in a small gas turbine is introduced. The internal flow is examined using high-speed imaging, laser-Doppler anemometry and computational fluid dynamics tools. The experimental and numerical results were analysed and compared in terms of the air core morphology and its temporal stability. Two different liquids were used, Kerosene-type Jet A-1 represented a commonly used fuel while p-Cymene (4-Isopropyltoluene) matched the refractive index of the Plexiglas atomizer body. The internal flow characteristics were set using dimensionless numbers i.e. the Reynolds number and Froude number. The flow test conditions were limited to inlet Reynolds numbers from 750 to 1750. Two atomizers were examined to represent a simplex and spill-return (SR) geometry. In a comparative manner, the SR atomizer features a central passage in the rear wall of the swirl chamber. The main advantage of this concept is that the fuel is always supplied to the swirl chamber at a high pressure therefore providing good atomization over a wide range of the injection flow rate. However, the presence of the spill orifice strongly affects the internal flow even if the spill-line is closed. The air core in the simplex atomizer was found fully developed and stable. The SR atomizer behaved differently, the air core didnot form at all, and the spray was therefore unstable.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4995
High-speed X-Ray Phase Contrast Imaging of String Cavitation in a Diesel Injector Orifice
Authors: Karathanassis Ioannis , Koukouvinis Phoevos , Lorenzi Massimo , Kontolatis Efstathios , Li Zhilong , Wang Jin , Mitroglou N. , Gavaises Manolis
Published: September 2017

The present investigation illustrates the temporally-resolved, phase-contrast visualization of the cavitating flowwithin an enlarged injector replica conducted at the ANL Advanced Photon Source. The flow was captured through side-view, x-ray radiographies at 67890 frames per second with an exposure time of 347ns. The orifice employed for the experiments has an internal diameter of 1.5mm and length equal to 5mm. A parametric investigation was conducted considering various combinations of the Reynolds and cavitation numbers, which designate the extent of in-nozzle cavitation. Proper post-processing of the obtained radiographies enabled the extraction of information regarding the shape and dynamical behaviour of cavitating strings. The average string extent along with its standard deviation was calculated for the entire range of conditions examined (Re=18000-36000, CN=1.6-7.7). Furthermore, the effect of the prevailing flow conditions on quantities indicative of the string dynamic behaviour such as the break-up frequency and lifetime was characterized and the local velocity field in the string region was obtained.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4996
Supercritical and transcritical real-fluid mixing using the PC-SAFT EOS
Authors: Rodriguez Carlos , Vidal Alvaro , Koukouvinis Phoevos , Gavaises Manolis
Published: September 2017

A numerical framework has been developed to simulate the mixing of supercritical and transcritical fluids using anequation of state based on statistical associating fluid theory. In a Diesel engine the liquid fuel is injected into supercritical air. After the injection, the Diesel is heated over its critical temperature reaching a supercritical state. Modelling real-fluid effects is critical in order to properly characterize the air/fuel mixing in the combustion chamber. By using the PC-SAFT EoS (Perturbed Chain Statistical Association Fluid Theory Equation of State) real fluids effects can be taken into account in a CFD simulation. The PC-SAFT EoS shows best results than cubic EoS computing liquid density, compressibility, speed of sound, vapor pressures and density derivatives. Unlike cubic EoS, this model accounts for the shape and size of the molecules. Gas, liquid, supercritical and vapor-liquid equilibrium states can be simulated. PT FLASH (Isothermal Multiphase Flash Calculation) is applied to compute the phase diagram used by the code. Shock tube problems were conducted in a wide range of pressures and densities using n-dodecane to show the capability of the developed algorithm. The results were compared with the solution of an exact Riemann solver which has the PC-SAFT EoS implemented showing a high degree of agreement. In addition, a two-dimensional simulation of supercritical nitrogen jet mixing was carried out to checkthe multidimensional capability of the code.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.5000
Analysis of PDA measurements in double injection GDI sprays
Authors: Araneo Lucio , Dondè Robert , Postrioti Lucio , Cavicchi Andrea
Published: September 2017

A N-heptane spray from a GDI multi-hole injector operated in ambient air at fixed conditions and with doubleinjection commands is studied with different experimental techniques to better understand the spray behaviors, focusing the analysis on the effect of different dwell times between the two pulses. Results from spray photographic analysis, fuel injected quantity, droplet velocity and sizing by Phase Doppler Anemometry are presented and compared.  The peculiarities and usefulness of a complementary application of the different techniques is illustrated. The two spray pulses have the same time length, so that the first spray evolves in a nearly quiescent and clean ambient, while the second, nominally identical to the first one, evolves in its trailing edge. The direct comparison allows an immediate perception of the differences among the two sprays, at the different dwell times, where the shorter tested, 160 microseconds, was chosen as the one that shows the first appreciable effect with at least one of the used techniques; the differences are clearly evident in the PDA results, sufficiently visible from the injection rate, not appreciable in the imaging at short distance. The effect of the longerdwell times becomes more evident and is illustrated.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.5007
Time resolved thermographic analysis of droplet impacts onto heated surfaces under extreme wetting scenarios
Authors: Moita Ana Sofia , Pontes Pedro , Teodori Emanuele , Moreira António Luís Nobre
Published: September 2017

The present paper explores the use of time resolved infrared IR thermography combined with high-speed imagingto describe the liquid-surface interfacial heat transfer phenomena occurring at droplet/wall interactions. Custom made calibration and post-processing methods are proposed and discussed. The results show that the methodology proposed captures very well particular details on droplet dynamics and heat transfer, allowing to identify air bubble trapping at the impact region as well as the temperature variations at the formation of the rim. Furthermore, the calibration proposed here allowed amending some physically incorrect results that were often obtained with the IR camera’s default calibration. The combined analysis of droplet dynamics (e.g. the spreading factor) with the radial temperature profiles, heat flux and cooling effectiveness computation allowed establishing qualitative and quantitative trends on the effect of various parameters on the heat transfer occurring at droplet/wall interactions. Particularly, the effect of the initial surface temperature is observed to play a minor role, as long as it is low enough to prevent the occurrence of boiling. On the other hand, extreme wetting scenarios, such as superhydrophobicity limit the heat transfer between the spreading droplet and the surface. However, the thermal analysis reveals that a major reason for this is not related to the reduced contact time of the droplet on the surface (due to rebound) or air entrapment, but is rather associated to the reduced wetted area caused by thehigh contact angles.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.5012
Towards Resolving the Atomization Process of an Idealized Fire Sprinkler with VOF Modeling
Authors: Meredith Karl Virgil , Zhou X. , Wang Y.
Published: September 2017

Fire suppression modeling depends on accurate characterization of the atomization processes of fire sprinklers.Numerical modeling, particularly the volume of fluid (VOF) method, has been applied to understanding the atomization behavior of an idealized sprinkler geometry consisting of a 9.5 mm inner-diameter cylindrical nozzle and a flat, 25.4 mm diameter disk with a liquid flow rate of 0.87 L/s. The simulations have been performed with an OpenFOAM based VOF solver, using the isoAdvector scheme for interfacial reconstruction. The sheet breakup distance and film thickness were calculated and compared with measurements from a previous study. A mesh refinement study identified the sensitivities in the predicted quantities to mesh resolution. This study enables furtherapplication of the model to simulation of the fully atomized spray.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.5014
Imaging of gasoline-like sprays with planar laser-induced exciplex fluorescence using a stereoscopic imaging system
Authors: Andersson Mats , Yamaguchi Akichika , Wang Hua
Published: September 2017

The role of the fuel injection systems in direct injected gasoline engines is to achieve a suitable fuel vapordistribution, homogeneous or with some degree of stratification, while avoiding unwanted effects such as wall wetting. Planar laser-induced exciplex fluorescence (PLIEF) is a method suitable for the characterization of such sprays since it enables separate imaging of both vapor and liquid phase of fuel simultaneously. In this study a hollow-cone spray generated with an outwards-opening piezo-actuated injector is investigated, with the injector mounted in a constant volume, constant pressure spray chamber with quartz windows, providing a controlled steady test environment. N-hexane is used as surrogate fuel of gasoline, together with exciplex-forming fluorescence tracers - fluorobenzene and diethylmethylamine. Fluorescence excitation is carried out with a parallel laser sheet from the fourth harmonic light of a Nd:YAG-laser (266 nm) running at 10 Hz. Exciplex fluorescence images from liquid phase and monomer fluorescence spray images from vapor phase can be acquired by a single UV-sensitive CMOS camera equipped with a stereoscope having filters selectively transmitting monomer fluorescence at 295 nm and exciplex fluorescence at 355 nm. Since the fluorescence is strongly quenched by oxygen, most of the experiments were carried out in a nitrogen atmosphere.Images were recorded during the injection and at various time steps after the end of the injection, and typical spray development for this type of injector was observed, i.e. the fuel forms an expanding cone, the sheet breaks up to form a vortex structure and the vortices continue to expand after the end of the injection. Fuel vapor is firstly observed at the same locations as the liquid drops, and is then accumulated into the center of the vortices. In addition, penetration of liquid phase and vapor phase are found to be very similar. Various injection pressures have been tested, which shows that increasing the fuel pressure from 10 to 20 MPa results in a larger vortex structure. The fuel evaporation can be followed by studying the evolution of the monomer and exciplex fluorescence as a function of time. At room temperature the vaporization is found to be very slow, but above 40°C there is a noticeablepresence of vapor at the end of the injection, and at higher temperatures, the vaporization goes even faster.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.5023
CFD simulations of the diesel jet primary atomization from a multihole injector
Authors: Chasos Charalambos
Published: September 2017

High pressure multi-hole diesel injectors are currently used in direct-injection common-rail diesel engines for the improvement of fuel injection and air/fuel mixing, and the overall engine performance. The resulting spray injection characteristics are dictated by the injector geometry and the injection conditions, as well as the ambient conditions into which the liquid is injected. The main objective of the present study was to design a high pressure multi-hole diesel injector and model the two-phase flow using the volume of fluid (VOF) method, in order to predict the initial liquid jet characteristics for various injection conditions. A computer aided design (CAD) software was employed for the design of the three-dimensional geometry of the assembly of the injector and the constant volume chamber into which the liquid jet emerges. A typical six-hole diesel injector geometry was modelled and the holes were symmetrically located around the periphery of the injector tip. The injector nozzle diameter and length were 0.2 mm and 1 mm, respectively, resulting in a ratio of nozzle orifice length over nozzle diameter L/D = 5. The commercial computational fluid dynamics (CFD) code STAR-CD was used for the generation of the computational mesh and for transient simulations with an Eulerian approach incorporating the VOF model for the two-phase flow and the Rayleigh model for the cavitation phenomenon. Three test cases for increasing injection pressure of diesel injection from the high pressure multi-hole diesel injector into high pressure and high temperature chamber conditions were investigated. From the injector simulations of the test cases, the nozzle exit velocity components were determined, along with the emerging liquid jet breakup length at the nozzle exit. Furthermore, the spray angle was estimated by the average radial displacement of the liquid jet and air mixture at the vicinity of the nozzle exit. The breakup length of the liquid jet and the spray cone angle which were determined from the simulations, were compared with the breakup length and cone angle estimated by empirical equations. From the simulations, it was found that cavitation takes place at the nozzle inlet for all the cases, and affects the fuel and air interaction at the upper area of the spray jet. Furthermore, the spray jet breakup length increases with elapsed time, and when the injection pressure increases both the breakup length and the spray cone angle increase.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.5040
Influence of Stokes Number on Collisional Interfacial Area Production Terms within the Σ-Y Eulerian Spray Atomization Model
Authors: Eichler Dominik , Pischke Philipp , Kneer Reinhold
Published: September 2017

The present study shows the effects of Stokes number on the modeling of collisional interfacial area productionterms within the Σ-Y model. This model can be employed for CFD simulations of high Weber and Reynolds number sprays using a RANS turbulence modeling. Within the model production of interfacial area is assumed to result from turbulent stretching and turbulent droplet collisions. The modeling of collisional processes requires the calculation of a characteristic turbulent collision velocity. In the present work this velocity was determined under consideration of Stokes number effects leading to turbulent droplet velocity fluctuations attenuated with respect to the gas phase fluctuations and including partial correlation between the velocities. The influence of this new modeling approach is tested within a 2D spray simulation by comparing the Sauter mean diameters observed to the ones obtained by employing the modeling approaches proposed in the literature which do not consider any Stokes number effects.The reduced collision velocites in the new modeling lead to higher values for Sauter mean diameters in the spray.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.5041
Evidence of vortex driven primary breakup in high pressure fuel injection
Authors: Shi Junmei , Aguado Lopez Pablo , Gomez Santos Eduardo , Guerrassi Noureddine , Dober Gavin , Bauer Wolfgang , Lai Ming-Chia , Wang Jin
Published: September 2017

This paper is to present a detailed case study on how the nozzle flow dynamics influences the primary breakup inthe spray formation process of diesel injection. The investigation was based on a 3-hole real-application nozzle with highly tapered injection holes using a URANS-LES (Large Eddy Simulation) hybrid approach in combination with the coupled Volume of Fluid (VOF) and Level Set method. High resolution LES was applied to simultaneously resolve the multi-scale nozzle flow dynamics downstream of the needle seat and the primary breakup process in the near-nozzle spray. Phase Contrast X-ray imaging (PCX) was applied to characterize the liquid-gas interfaces in the near-nozzle spray for validation purposes. The results provide detailed information on how the vortex shedding and vortex interactions in the injection hole drives the jet deformation, ligament anddroplet formation in the primary breakup process.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.5707
Dilute polymer solution drops impacting on heated surfaces: New impact morphologies and impact regime maps
Authors: Bertola Volfango , Lakhanpal Chetan
Published: September 2017

The impact morphology of dilute polymer solution drops on a heated surface is studied experimentally by meansof high-speed imaging, with respect to the following parameters: surface temperature; impact Weber number; polymer concentration; polymer molecular weight. In addition to impact morphologies observed in Newtonian drops (deposition, rebound, secondary atomisation and breakup/splashing), three new impact regimes have been identified: (i) a single satellite droplet ejected in the direction of bouncing but tethered to the main drop by a thin liquid filament; (ii) a splashing-like behaviour (semi-splashing), where the rim instability  generates  satellite droplets tethered to the lamella by thin liquid filaments; (iii) a spray-like behaviour (semi-spray), where a fine secondary atomisation generated upon impact is quickly absorbed back into the drop globule. Experiments were carried out using drops of aqueous polyethylene oxide (PEO) solutions, with mass concentrations of 100 ppm, 200 ppm and 400 ppm, and PEO molecular weights of 2 MDa, 4MDa, and 8MDa. The impact morphology on a polished aluminium surface with temperatures ranging between 160°C and 400°C was investigated for impact Weber numbers between 20 and 170, taking side view images of impacting drops at a rate of 1,000 frames persecond.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4905
Ecología, biotecnología y taxonomía de ectomicorriza para la conservación y aprovechamiento de Abies religiosa en zonas templadas de México
Authors: Oros-Ortega Iván , Andrade-Torres Antonio , Lara-Pérez Luis A. , Guzmán-Olmos Rubén F. , Casanova-Lugo Fernando , Sáenz-Carbonell Luis A. , Córdova-Lara Iván
Published: September 2017

Las poblaciones endémicas de Abies religiosa (abeto, oyamel) poseen gran importancia económica, ecológica y social; además, forman distintas interacciones con microorganismos edáficos, principalmente con hongos ectomicorrizógenos. Actualmente, las poblaciones aisladas (i. e. oyamel) están amenazadas por la deforestación, la expansión agrícola y el calentamiento global; por lo cual, es urgente entender las interacciones ecológicas y evolutivas con hongos ectomicorrizógenos. El objetivo de la presente investigación fue analizar el uso de la ecología, taxonomía y biología molecular de ectomicorrizas para comprender el papel que juegan estos hongos en árboles de A. religiosa en México. Se presentan áreas de oportunidad de investigación, así como los principales vacíos de información de la caracterización morfoanatómica/molecular, taxonomía y evolución de la simbiosis ectomicorrízica en bosques de A. religiosa. Para lo anterior, se reunió información de 108 taxa de hongos potencialmente ectomicorrizógenos, colectados en diferentes poblaciones de abetos. Los taxa con potencial alto para inocular A. religiosa son Sebacina dimitica, Clavulina cf. cinerea, Membranomyces sp., Thelephoraceae, Russula spp., Ramaria spp., Lactarius spp. e Inocybe spp. Finalmente, se discuten aspectos que faltan por resolver para determinar su potencial de uso, manejo, conservación y aprovechamiento de A. religiosa en zonas templadas de México. Este problema puede resolverse combinando herramientas moleculares con la descripción morfológica e histológica de morfotipos ectomicorrizógenos. Adicionalmente, se requieren metodologías que permitan estandarizar resultados para llegar a conclusiones más sólidas sobre las interacciones micorrízicas.
Landscape pattern analysis of the urban forest and green network structure in the Pudong district of Shanghai, China
Authors: Wang Jianan , Liu Hui , Wu Zemin , Li Yingying
Published: September 2017

Introducción: La urbanización ha alterado el paisaje natural del mundo. En China, la expansión urbana ha incrementado rápidamente.Objetivo: Analizar el patrón del paisaje del bosque urbano y la estructura de la red ecológica en el distrito de Pudong en Shanghái, China.Materiales y métodos: El área de estudio abarcó 553 km2, la cual incluyó 253 km2 de área urbanizada. Las características estructurales se analizaron utilizando Landsat 7 2008TM, 2007 Spot Image, Google Earth y City Maps. Los patrones del paisaje del bosque urbano y la estructura de la red ecológica se interpretaron con el software ArcGIS.Resultados y discusión: El área de los parches forestales urbanos (> 900 m2) y el área urbanizada en el distrito representaron 5.15 y 5.78 %, respectivamente. La red de corredores verdes urbanos fue de 80.27 km2 con densidad de 1.99 km·km-2. La conexión de la red ecológica fue de 1.30, el circuito de 0.19 y la conectividad de 0.47. La cubierta de dosel forestal fue de 7.02 % en toda el área de estudio y 10.27 % en el área urbanizada. La cubierta puede alcanzar 8.68 a 9.79 % en el área total de estudio, y 11.49 a 12.3 % en el área urbanizada.Conclusión: La red ecológica está construida, pero no fue bien diseñada, por lo que es necesario mejorar su estructura. Los árboles existentes no pueden modificar el ambiente forestal para toda el área urbanizada. La plantación de árboles es factible, para aumentar la cubierta de dosel forestal.
Modelo de selección y evaluación de aspirantes a un posgrado en ciencias forestales
Authors: Zamudio-Sánchez Francisco J. , Romo-Lozano José Luis , Borja-de la Rosa Amparo , Martínez-Gómez Gladys , Ávalos-Vargas Adriana
Published: September 2017

Introducción: El proceso de admisión de estudiantes al posgrado es muy importante para el mejoramiento de los indicadores de mayor ponderación en la calidad del programa. El problema es la gran cantidad de información solicitada que no siempre se considera objetivamente para la selección de aspirantes con el perfil deseado.Objetivo: Analizar modelos de evaluación para seleccionar aspirantes al posgrado y, vía una métrica, elegir el modelo más compatible.Materiales y métodos: Se utilizó información de 19 solicitantes de ingreso al programa de la Maestría en Ciencias Forestales de la Universidad Autónoma Chapingo. Se aplicaron métodos subjetivos de análisis multicriterio en la fase de ponderación de los criterios (3) y subcriterios (8): método de asignación de puntos y proceso jerárquico analítico. Los valores fueron agregados mediante el método TOPSIS y el método de suma ponderada. La combinación ponderación-agregación más compatible se determinó con el ordenamiento de Pareto.Resultados y discusión: La combinación del método de la suma ponderada y el proceso jerárquico analítico presentó una distancia promedio menor al ordenamiento del resto de las combinaciones y, consecuentemente, generó una selección de aspirantes más compatible con los criterios de selección.Conclusión: Los métodos multicriterio representan una buena opción para considerar apropiadamente la cantidad de información generada en un proceso de selección.
The genesis of Hurricane Nate and its interaction with a nearby environment of very dry air
Authors: Rutherford Blake , Dunkerton Timothy , Montgomery Michael , Braun Scott
Published: September 2017

Abstract. The interaction of a tropical disturbance with its environment is thought to play an important role in whether a disturbance will develop or not. Most developing disturbances are somewhat protected from the intrusion of environmental dry air at mid-levels. For African easterly wave (AEW) disturbances, the protective boundary is approximated by closed streamlines in the wave-relative frame, and their interior is called the wave pouch. The dynamic and thermodynamic processes of spin-up occur inside the pouch. In this study, we define the kinematic boundaries for a non-AEW disturbance in the Bay of Campeche that originated along a sharp frontal boundary in a confluent region of low pressure. We examine these boundaries during the genesis of Hurricane Nate (2011) to show how a pouch boundary on isobaric levels in the Lagrangian frame may allow for some transport into the pouch along the frontal boundary while still protecting the innermost development region. This result illustrates a generic property of weakly unsteady flows, including the time-dependent critical layer of AEWs, that lateral exchange of air occurs along a segment of the boundary formed by the instantaneous, closed translating streamlines. Transport in the Lagrangian frame is simplest when measured with respect to the stable and unstable manifolds of a hyperbolic trajectory, which are topologically invariant. In this framework, an exact analysis of vorticity transport identifies the primary source as the advection of vorticity through the entrainment and expulsion of bounded material regions called lobes. We also show how these Lagrangian boundaries impact the concentration of moisture, influence convection, and contribute to the pouch vertical structure.
Reconstruction and analysis of erythemal UV radiation time series from Hradec Králové (Czech Republic) over the past 50 years
Authors: Čížková Klára , Láska Kamil , Metelka Ladislav , Staněk Martin
Published: September 2017

Abstract. This paper evaluates the variability of erythemal ultraviolet (EUV) radiation from Hradec Králové (Czech Republic) in the period 1964–2013. The EUV radiation time series was reconstructed using a radiative transfer model and additional empirical relationships with the root mean square error of 9.9 %. The reconstructed time series documented the increase in EUV radiation doses in the 1980s and the 1990s (up to 15 % per decade), which is linked to the steep decline in total ozone (10 % per decade). The changes of cloud cover were the major factor affecting the EUV radiation doses especially in the 1960s, 1970s, and at the beginning of the new millennium. The mean annual EUV radiation doses in the decade 2004–2013 declined by 5 %. The factors affecting the EUV radiation doses differed also according to the chosen integration period (daily, monthly, and annually): solar zenith angle was the most important for daily doses, cloud cover for their monthly means, and the annual means of EUV radiation doses were most influenced by total ozone column. The number of days with very high EUV radiation doses increased by 22 % per decade, the increase was statistically significant in all seasons except autumn. The occurrence of the days with very high EUV doses was influenced mostly by low total ozone column (82 % of days), clear-sky or partly cloudy conditions (74 % of days) and by increased surface albedo (19 % of days). The principal component analysis documented that the occurrence of days with very high EUV radiation doses was much affected by the positive phase of North Atlantic Oscillation with an Azores High promontory reaching over central Europe. In the stratosphere, a strong Arctic circumpolar vortex and also the meridional inflow of ozone-poor air from the south-west were favorable for the occurrence of days with very high EUV radiation doses. This is the first analysis of the relationship between the high EUV radiation doses and macro-scale circulation patterns, and therefore more attention should be given also to other dynamical variables that may affect the solar UV radiation on the Earth surface.
Combined retrieval of Arctic liquid water cloud and surface snow properties using airborne spectral solar remote sensing
Authors: Ehrlich André , Bierwirth Eike , Istomina Larysa , Wendisch Manfred
Published: September 2017

Abstract. The passive solar remote sensing of cloud properties over highly reflecting ground is challenging, mostly due to the low contrast between the cloud reflectivity and that of the underlying surfaces (sea ice and snow). Uncertainties in the retrieved cloud optical thickness τ and cloud droplet effective radius reff, C may arise from uncertainties in the assumed spectral surface albedo, which is mainly determined by the generally unknown effective snow grain size reff, S. Therefore, in a first step the effects of the assumed snow grain size are systematically quantified for the conventional bispectral retrieval technique of τ and reff, C for liquid water clouds. In general, the impact of uncertainties of reff, S is largest for small snow grain sizes. While the uncertainties of retrieved τ are independent of the cloud optical thickness and solar zenith angle, the bias of retrieved reff, C increases for optically thin clouds and high Sun. The largest deviations between the retrieved and true original values are found with 83 % for τ and 62 % for reff, C. In the second part of the paper a retrieval method is presented that simultaneously derives all three parameters (τ, reff, C, reff, S) and therefore accounts for changes in the snow grain size. Ratios of spectral cloud reflectivity measurements at the three wavelengths λ1 = 1040 nm (sensitive to reff, S), λ2 = 1650 nm (sensitive to τ), and λ3 = 2100 nm (sensitive to reff, C) are combined in a trispectral retrieval algorithm. In a feasibility study, spectral cloud reflectivity measurements collected by the Spectral Modular Airborne Radiation measurement sysTem (SMART) during the research campaign Vertical Distribution of Ice in Arctic Mixed-Phase Clouds (VERDI, April/May 2012) were used to test the retrieval procedure. Two cases of observations above the Canadian Beaufort Sea, one with dense snow-covered sea ice and another with a distinct snow-covered sea ice edge are analysed. The retrieved values of τ, reff, C, and reff, S show a continuous transition of cloud properties across snow-covered sea ice and open water and are consistent with estimates based on satellite data. It is shown that the uncertainties of the trispectral retrieval increase for high values of τ, and low reff, S but nevertheless allow the effective snow grain size in cloud-covered areas to be estimated.
Intercomparison study and optical asphericity measurements of small ice particles in the CERN CLOUD experiment
Authors: Nichman Leonid , Järvinen Emma , Dorsey James , Connolly Paul , Duplissy Jonathan , Fuchs Claudia , Ignatius Karoliina , Sengupta Kamalika , Stratmann Frank , Möhler Ottmar , Schnaiter Martin , Gallagher Martin
Published: September 2017

Abstract. Optical probes are frequently used for the detection of microphysical cloud particle properties such as liquid and ice phase, size and morphology. These properties can eventually influence the angular light scattering properties of cirrus clouds as well as the growth and accretion mechanisms of single cloud particles. In this study we compare four commonly used optical probes to examine their response to small cloud particles of different phase and asphericity. Cloud simulation experiments were conducted at the Cosmics Leaving OUtdoor Droplets (CLOUD) chamber at European Organisation for Nuclear Research (CERN). The chamber was operated in a series of multi-step adiabatic expansions to produce growth and sublimation of ice particles at super- and subsaturated ice conditions and for initial temperatures of −30, −40 and −50 °C. The experiments were performed for ice cloud formation via homogeneous ice nucleation. We report the optical observations of small ice particles in deep convection and in situ cirrus simulations. Ice crystal asphericity deduced from measurements of spatially resolved single particle light scattering patterns by the Particle Phase Discriminator mark 2 (PPD-2K, Karlsruhe edition) were compared with Cloud and Aerosol Spectrometer with Polarisation (CASPOL) measurements and image roundness captured by the 3View Cloud Particle Imager (3V-CPI). Averaged path light scattering properties of the simulated ice clouds were measured using the Scattering Intensity Measurements for the Optical detectioN of icE (SIMONE) and single particle scattering properties were measured by the CASPOL. We show the ambiguity of several optical measurements in ice fraction determination of homogeneously frozen ice in the case where sublimating quasi-spherical ice particles are present. Moreover, most of the instruments have difficulties of producing reliable ice fraction if small aspherical ice particles are present, and all of the instruments cannot separate perfectly spherical ice particles from supercooled droplets. Correlation analysis of bulk averaged path depolarisation measurements and single particle measurements of these clouds showed higher R2 values at high concentrations and small diameters, but these results require further confirmation. We find that none of these instruments were able to determine unambiguously the phase of the small particles. These results have implications for the interpretation of atmospheric measurements and parametrisations for modelling, particularly for low particle number concentration clouds.
Nanodust dynamics during a coronal mass ejection
Authors: Czechowski Andrzej , Kleimann Jens
Published: September 2017

Abstract. The dynamics of nanometer-sized grains (nanodust) is strongly affected by electromagnetic forces. High-velocity nanodust was proposed as an explanation for the voltage bursts observed by STEREO. A study of nanodust dynamics based on a simple time-stationary model has shown that in the vicinity of the Sun the nanodust is trapped or, outside the trapped region, accelerated to high velocities. We investigate the nanodust dynamics for a time-dependent solar wind and magnetic field configuration in order to find out what happens to nanodust during a coronal mass ejection (CME). The plasma flow and the magnetic field during a CME are obtained by numerical simulations using a 3-D magnetohydrodynamic (MHD) code. The equations of motion for the nanodust particles are solved numerically, assuming that the particles are produced from larger bodies moving in near-circular Keplerian orbits within the circumsolar dust cloud. The charge-to-mass ratios for the nanodust particles are taken to be constant in time. The simulation is restricted to the region within 0.14 AU from the Sun. We find that about 35 % of nanodust particles escape from the computational domain during the CME, reaching very high speeds (up to 1000 km s−1). After the end of the CME the escape continues, but the particle velocities do not exceed 300 km s−1. About 30 % of all particles are trapped in bound non-Keplerian orbits with time-dependent perihelium and aphelium distances. Trapped particles are affected by plasma ion drag, which causes contraction of their orbits.
floodX: urban flash flood experiments monitored with conventional and alternative sensors
Authors: Moy de Vitry Matthew , Dicht Simon , Leitão João P.
Published: September 2017

Abstract. The data sets described in this paper provide a basis for developing and testing new methods for monitoring and modelling urban pluvial flash floods. Pluvial flash floods are a growing hazard to property and inhabitants' well-being in urban areas. However, the lack of appropriate data collection methods is often cited as an impediment for reliable flood modelling, thereby hindering the improvement of flood risk mapping and early warning systems. The potential of surveillance infrastructure and social media is starting to draw attention for this purpose. In the floodX project, 22 controlled urban flash floods were generated in a flood response training facility and monitored with state-of-the-art sensors as well as standard surveillance cameras. With these data, it is possible to explore the use of video data and computer vision for urban flood monitoring and modelling. The floodX project stands out as the largest documented flood experiment of its kind, providing both conventional measurements and video data in parallel and at high temporal resolution. The data set used in this paper is available at https://doi.org/10.5281/zenodo.830513.
The benefit of seamless forecasts for hydrological
predictions over Europe
Authors: Wetterhall Fredrik , Di Giuseppe Francesca
Published: September 2017

Abstract. Two different systems provide long range forecasts at ECMWF. On the sub-seasonal time scale, ECMWF issues an extended-range ensemble prediction system (ENS-ER) which runs a 46-day forecast integration issued twice weekly. On longer time scales the current seasonal forecasting system (SYS4) produces a 7-month outlook starting from the first of each month. SYS4 uses an older model version and has lower spatial and temporal resolution than ENS-ER. Given the substantial differences between the ENS-ER and the SYS4 configurations and the difficulties of creating a seamless integration, applications that rely on weather forcing as input such as the European Flood Awareness System (EFAS) often follow the route of the creation of two separate systems for different forecast horizons. This study evaluates the benefit of a seamless integration of the two systems for hydrological applications and shows that the benefit of the new seamless system when compared to the seasonal forecast can be attributed to (1) the use of a more recent model version in the sub-seasonal range (first 46 days) and (2) the much more frequent updates of the meteorological forecast.
Structural analysis of S-wave seismics around an urban sinkhole; evidence of enhanced subrosion in a strike-slip fault zone
Authors: Wadas Sonja H. , Tanner David C. , Polom Ulrich , Krawczyk Charlotte M.
Published: September 2017

Abstract. In November 2010, a large sinkhole opened up in the urban area of Schmalkalden, Germany. To determine the key factors which benefited the development of this collapse structure and therefore the subrosion, we carried out several shear wave reflection seismic profiles around the sinkhole. In the seismic sections we see evidence of the Mesozoic tectonic movement, in the form of a NW–SE striking, dextral strike-slip fault, known as the Heßleser Fault, which faulted and fractured the subsurface below the town. The strike-slip faulting created a zone of small blocks (
Deeply subducted continental fragments: I. Fracturing, dissolution-precipitation and diffusion processes recorded by garnet textures of the central Sesia Zone (Western Italian Alps)
Authors: Giuntoli Francesco , Lanari Pierre , Engi Martin
Published: September 2017

Abstract. Complex zoning in garnet from micaschists of the Sesia Zone (Western Italian Alps) preserves evidence of two orogenic cycles and provides detailed insights into resorption, growth and diffusion processes induced by fluid pulses at high pressure. Data on local textures and mineral chemistry are combined with data derived from thermodynamic modelling to understand and quantify these processes. Garnet shows low-Ca porphyroclastic cores that are stable at (Permian) granulite facies conditions. In one sample, the first garnet rim that surrounds the pre-Alpine granulite facies core indicates that pre-Alpine amphibolite facies metamorphism followed the granulite facies event. The cores show lobate edges and preserve inner fractures, which are sealed by high pressure Alpine garnet. This observation suggests that during the first stages of subduction, before hydration of these high temperature rocks, brittle failure of the garnet occurred, implying high strain rates. Several Alpine rims show different textures indicative of interaction with hydrous fluid: (a) resorption-dominated textures produced lobate edges, at the expense of the outer part of the granulite core; (b) peninsulas and atoll garnets are produced by replacement reactions; (c) spatially limited resorption and enhanced transport of elements due the fluid phase is evident along brittle fractures and their immediate proximity. Thermodynamic modelling shows that all of these Alpine rims formed at eclogite facies conditions. Structurally controlled samples allow these fluid-garnet interaction phenomena to be traced across a portion of the Sesia Zone, with decreasing in fluid-garnet interaction toward external areas (NW). Replacement of the Permian HT assemblages by hydrate-rich Alpine assemblages can reach nearly 100%. However, no clear relationship is visible between deformation structures and fluids that triggered eclogite facies metamorphism; suggesting disperse fluid flow.
Periodicity in the BrO/SO2 molar ratios in the volcanic gas plume of Cotopaxi and its correlation with the Earth tides during the eruption in 2015
Authors: Dinger Florian , Bobrowski Nicole , Warnach Simon , Bredemeyer Stefan , Hidalgo Silvana , Arellano Santiago , Galle Bo , Platt Ulrich , Wagner Thomas
Published: September 2017

Abstract. We evaluated NOVAC (Network for Observation of Volcanic and Atmospheric Change) gas emission data from the 2015 eruption of Cotopaxi volcano (Ecuador) for BrO/SO2 molar ratios. Statistical analysis of the data revealed a conspicuous periodic pattern with a periodicity of about two weeks in a three month time series. While the time series is too short to rule out a chance recurrence of transient geological or meteorological events as a possible origin for the periodic signal, we nevertheless took this observation as a motivation to examine the influence of natural forcings with periodicities of around two weeks on volcanic gas emissions. One strong aspirant with such a periodicity are the Earth tides, which are thus central in this study. We present the BrO/SO2 data, analyse the reliability of the periodic signal, discuss a possible meteorological or eruption-induced origin of this signal, and compare the signal with the theoretical ground surface displacement pattern caused by the Earth tides. Central result is the observation of a significant correlation between the BrO/SO2 molar ratios with the North-South and vertical components of the calculated tide-induced surface displacement with correlation coefficients of 47 % and 36 %, respectively. From all other investigated parameters, only the correlation between the BrO/SO2 molar ratios and the relative humidity in the local atmosphere resulted in a comparable correlation coefficient of about 33 %.
Ice bridges and ridges in the Maxwell-EB sea ice rheology
Authors: Dansereau Véronique , Weiss Jérôme , Saramito Pierre , Lattes Philippe , Coche Edmond
Published: September 2017

Abstract. This paper presents a first implementation of a new rheological model for sea ice on geophysical scales. This continuum model, called Maxwell elasto-brittle (Maxwell-EB), is based on a Maxwell constitutive law, a progressive damage mechanism that is coupled to both the elastic modulus and apparent viscosity of the ice cover and a Mohr–Coulomb damage criterion that allows for pure (uniaxial and biaxial) tensile strength. The model is tested on the basis of its capability to reproduce the complex mechanical and dynamical behaviour of sea ice drifting through a narrow passage. Idealized as well as realistic simulations of the flow of ice through Nares Strait are presented. These demonstrate that the model reproduces the formation of stable ice bridges as well as the stoppage of the flow, a phenomenon occurring within numerous channels of the Arctic. In agreement with observations, the model captures the propagation of damage along narrow arch-like kinematic features, the discontinuities in the velocity field across these features dividing the ice cover into floes, the strong spatial localization of the thickest, ridged ice, the presence of landfast ice in bays and fjords and the opening of polynyas downstream of the strait. The model represents various dynamical behaviours linked to an overall weakening of the ice cover and to the shorter lifespan of ice bridges, with implications in terms of increased ice export through narrow outflow pathways of the Arctic.
Caracterización Glaciológica de Chile
Authors: Segovia Rocha Alexis Andrés , Videla Giering Yohann Alfredo
Published: September 2017

Se realizó una caracterización glaciológica de Chile, la cual incluyó la determinación del número, superficie y el equivalente en agua contenida en los glaciares a nivel nacional (Incluidos los glaciares rocosos y campos de hielo patagónicos). La caracterización glaciológica de Chile se realizó mediante datos extraídos del Inventario Nacional de Glaciares de la Dirección General de Aguas (DGA) con actualización al año 2014, generación de información en base a procesamiento del inventario de glaciares e información bibliográfica. Dentro de los resultados, se pudo establecer que Chile posee un total estimado de 24.114 glaciares con una superficie de 23.641 km2. No obstante, esta cantidad de hielo se manifiesta con grandes diferencias regionales a lo largo del país, aumentando de norte a sur. El equivalente en agua contenida de todos los cuerpos de hielo a nivel nacional corresponde a un total

estimado de 3.175 km3.