Laboratory measurements of the sedimentation velocity of hexagonal planar ice crystals

New experimental measurements of the falling velocity, size and orientation of individual hexagonal plate-like ice crystals are reported. The measurements were conducted at three different temperatures: −13, −16 and −20 °C. The diameter of the ice crystals measured in the experiments were between 50 μm and 250 μm, a size range which is in agreement with the size found in natural clouds. In this range, ice crystals show a random orientation during free fall and a falling velocity which increases with size. Results show that the fall velocity is insensitive to the temperature at which the ice crystals grow for the temperatures used in this study. An empirical power-law between the Best and Reynolds numbers is presented using the capacitance as characteristic length and an estimation of the ice crystal mass. Despite the dispersion of the experimental data, the Best–Reynolds relationship found seems to be similar to the relationship for falling spheres in Stokes flow using the capacitance as the hydrodynamic radius. The fall velocities of hexagonal and columnar ice crystals were compared. The columnar ice crystals show a velocity larger than that of hexagonal ice crystals with the same value of capacitance. However, both crystalline habits show a unique empirical Be–Re relationship.Fil: Burgesser, Rodrigo Exequiel. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; ArgentinaFil: Castellano, Nesvit Edit. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentin

Sedimentation analysis of columnar ice crystals in viscous flow regimes

The sedimentation process of columnar ice crystals was evaluated using data obtained by the lattice Boltzmann method. The data used correspond to columnar ice crystals with maximum dimension less than 100 μm and aspect ratios between 1 and 3. The terminal velocity was computed for different ice-crystal bulk densities and for three falling orientations. The analysis corresponds to ice crystals falling in viscous flow regimes, where theoretical formulations overestimate the terminal velocity. Different characteristic lengths of columnar ice crystals and different theoretical proposals for the sedimentation process were tested in order to find the best representation of the data. Characteristic lengths reported in the literature do not represent the sedimentation process for all the falling orientations used in this study. Thus, it was not possible to obtain a unique relation between the Best and Reynolds numbers. In particular, columnar ice crystals falling with their longer dimension parallel to the vertical direction show a large dispersion that it does not seem possible to reduce. The theoretical and semi-empirical formulations of the terminal velocity evaluated show large deviations in the computed velocity, with a strong dependence on ice-crystal aspect ratio. The dispersion observed seems to be intrinsically related to the dimensionless variables used to parametrize the terminal velocity. To derive a unique scale law that could represent the sedimentation process of ice crystals, geometric, kinematic, and dynamic similarities are required. However, these conditions are not fulfilled in the sedimentation process.Fil: Burgesser, Rodrigo Exequiel. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; ArgentinaFil: Giovacchini, Juan Pablo. Ministerio de Defensa. Instituto Universitario Aeronautico de la Faa; ArgentinaFil: Castellano, Nesvit Edit. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentin

Gateway Pacific Terminal Proposal: Environmental Impact Assessment

SSA Marine seeks to construct a full-service dry bulk commodity shipping terminal at Cherry Point, Washington. The proposed terminal will be the largest of its kind on the West Coast of the United States. If fully constructed, the terminal will have the capacity to annually export 54 million metric tons of bulk commodities, 48 million metric tons of which are expected to be coal (McKay). The project will involve constructing a railcar unloading station, stockyard, conveyance and shiploading systems, berths for three vessels, service buildings, and a storage and material handling facility, as well as making improvements to rail access at the site. The terminal will likely be constructed in two or more phases, depending on the initial customer demand (SSA Marine)

Prevalence of feline herpesvirus 1, feline calicivirus and Chlamydophila felis in clinically normal cats at a Korean animal shelter

The prevalence of feline herpesvirus-1 (FHV-1), feline calicivirus (FCV), and Chlamydophila (C.) felis was studied in cats of an animal shelter in Korea. Total 78 cats without ocular and upper respiratory tract disease were examined. Specimens were obtained from ocular conjunctiva and oropharynx. Using multiplex polymerase chain reaction (PCR) and reverse transcription PCR, three pathogens were simultaneously detected. In examined 78 cats, 49 (63%) cats were positive for FHV-1. However, all specimens were negative for C. felis and FCV. In conclusion, many cats recovered from FHV-1 infection remain subclinical carriers in shelter environment

Laboratory measurements of ice nuclei particle concentration in the range of − 29 to − 48 °C

This work quantifies the natural ice nuclei particle (INP) concentration activated at temperatures (T) lower than −29 °C in Córdoba, a city located in a semiarid region in the center of Argentina. Laboratory INP concentration measurements were performed in a cloud chamber where water supersaturation was reached by an adiabatic isobaric mixture of two air masses with different relative humidities. Once the activated INPs grew up to form ice crystals, these crystals were detected and quantified due to the sparkles they produce when they reflect the light incident on them. Following this methodology, a total of 123 ice crystal (i.e. INP) concentration measurements were performed at a T range of −29 °C to −48 °C.From these measurements it was found that the values of the INP concentration increased with T between −29 °C and approximately −38 °C, but they remained almost constant with T between −38 °C and − 48 °C. This behavior could be related to the dependence of the number of active sites with T. The INP concentration measurements obtained in this work were compared with those reported in recent studies. In addition, considering the elemental composition of the particulate matter in the site of study, we hypothesized that aluminosilicate minerals could be responsible for the INP measurements presented. This assumption was also made by comparing the obtained measurements with different parameterizations reported in the literature. Even though this hypothesis deserves to be tested, this study reports the first INP concentration measurements at temperatures lower than −30 °C in Argentina being one of the few works reporting such measures in the Southern Hemisphere.Fil: Lopez, Maria Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; ArgentinaFil: Burgesser, Rodrigo Exequiel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentin

Suitable regions for assessing long term trends in lightning activity

The efficiency and stability of global lightning data are not yet sufficient to provide accurate estimates of long term trends in lightning activity. In contrast, regional lightning networks are generally both efficient and stable. Regions with a low level of interannual variability are well suited to the identification of trends in lightning activity. Satellite lightning data are used to identify countries in South America which display only mild interannual variability. These countries are candidates for regional studies of long term trends in lightning activity. These trends can be linked to climate change.Fil: Collier, A. B.. University of KwaZulu-Natal; SudáfricaFil: Burgesser, Rodrigo Exequiel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; ArgentinaFil: Avila, Eldo Edgardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentin

Spatial and time distribution of the flash rate over tropical Africa

The lightning flash rate over tropical Africa was analyzed using lightning data of two independent lightning detection systems, the World Wide Lightning Location Network and the Lightning Imaging Sensor. Spatial and time distributions of lightning activity were studied using different spatial and temporal scales. Results show a very localized high-lightning activity center on the west side of the Albertine Rift Mountain, located east of the Congo Basin, and substantial lightning activity in the center of the region. Both centers show low variations on the lightning activity throughout the year and a marked diurnal cycle with a maximum lightning activity in the local afternoon. A secondary lightning activity center was found over Lake Victoria, which has an annual variation similar to that of the Congo Basin lightning activity centers but does not show a marked diurnal cycle. The lightning activities observed seem to be strongly influenced by topography and are in agreement with the small temperature ranges and with the rainfall observed in the region.Fil: Burgesser, Rodrigo Exequiel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; ArgentinaFil: Nicora, Maria Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones Científicas y Técnicas para la Defensa. Centro de Investigación en Láseres y Aplicaciones; ArgentinaFil: Avila, Eldo Edgardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentin

Surface temperature distribution on a spherical ice particle growing by accretion in wet growth regime

Experimental evidence has demonstrated that temperature on the surface of an ice particle growing by accretion is not uniform. This non-uniformity is relevant because the ice particle surface temperature is an important microphysical parameter that influences the sign and magnitude of the charge transfer during ice particles collisions. In particular, when high values of ambient temperature and liquid water content are reached, the ice particle surface temperature is expected to reach 0 °C, which is known as wet growth regime. Previous experimental results have shown that wet growth is not uniformly reached on the ice particle surface and a surface temperature distribution is developed. In order to know the surface temperature distribution of a fixed ice particle growing by accretion of supercooled water, numerical calculations were carried out. It was found that the surface temperature distribution has a strong dependence on liquid water content, ambient temperature, airflow velocity and water droplet size. The stagnation point always reaches higher temperatures and, in many cases, its temperature is near 0 °C. For some values of the liquid water content, ambient temperature and airflow velocity, it was possible to determine temperature differences up to 7 °C between the stagnation point and the equator. This variation in the surface temperature implies that the region near the stagnation point would experience wet growth, while the rest of the ice particle surface would remain in dry growth regime, supporting the partial wet growth hypothesis. This could also explain the charge transfer reported during ice particles collisions under wet growth conditions.Fil: Luque, Melina Yasmín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; ArgentinaFil: Burgesser, Rodrigo Exequiel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; ArgentinaFil: Castellano, Nesvit Edit. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentin

The growth of ice particles in a mixed phase environment based on laboratory observations

This paper describes new laboratory observations about the size evolution of ice crystals and cloud droplets immersed in a mixed-phase cloud. The experiments were performed by using a cloud chamber facility for three temperatures − 6 °C, − 10 °C and − 20 °C, in order to explore the basic crystal growth habits (columns and hexagonal plates). The sizes of the cloud droplets, ice-columns and hexagonal ice-plates were examined for growth times between 50 and 300 s. The results show evidence that after ice crystal nucleation, the cloud droplets reduce gradually their sizes by the evaporation process; while the ice crystals grow as a consequence of the water vapor diffusion process. The ice crystal growths at different temperatures were compared with the results reported by other authors. The experimental data were also compared with a theoretical model of the growth rate of ice crystals. It was observed that the numerical model provides a description of the ice columns' growth in fairly good agreement with the laboratory observations, while it predicts that the hexagonal plates evolve with maximum sizes larger than those observed in the experiments. In general, it has been noted that the results obtained from the model are very sensitive to the parameter that denotes the ratio between the condensation coefficient for the basal face and prism face. It is a critical coefficient that needs to be carefully addressed in cloud modeling.Fil: Castellano, Nesvit Edit. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Avila, Eldo Edgardo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; ArgentinaFil: Burgesser, Rodrigo Exequiel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; ArgentinaFil: Saunders, Clive P.R.. University of Manchester; Reino Unid

Actividad eléctrica asociada a la erupción del complejo volcánico Cordón Caulle durante 2011

Se realizó un estudio de la actividad eléctrica generada por la erupción del complejo volcánico Cordón Caulle en junio de 2011 utilizando datos de descargas eléctricas detectadas por la red World Wide Lightning Location Network. La actividad eléctrica observada se corresponde a descargas eléctricas generadas en la pluma volcánica con una buena correlación entre la cantidad de descargas y la altura de la misma. Aunque la actividad eléctrica detectada fue baja, los resultados están de acuerdo con los obtenidos por estudios previos y muestran que puede ser usada como un indicador de la actividad volcánica. Además muestra la factibilidad de utilizar la red para una detección temprana de erupciones volcánicas.Fil: Nicora, Maria Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Unidad de Investigación y Desarrollo Estratégicos para la Defensa; Argentina;Fil: Burgesser, Rodrigo Exequiel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - CONICET - Córdoba. Instituto de Fisica Enrique Gaviola; Argentina;Fil: Rosales, Alejandro. Universidad Nacional de la Patagonia; Argentina;Fil: Quel, Eduardo Jaime. Consejo Nacional de Investigaciones Científicas y Técnicas. Unidad de Investigación y Desarrollo Estratégicos para la Defensa; Argentina;Fil: Avila, Eldo Edgardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - Conicet - Cordoba. Instituto de Fisica Enrique Gaviola; Argentina