Laboratory evidence for volume-dominated nucleation of ice in supercooled water microdroplets

International audienceWe report on measurements of the rate of homogeneous ice nucleation in supercooled water microdroplets levitated in an electrodynamic balance. By comparison of the freezing probability for droplets of radius 49µm and 19µm, we are able to conclude that homogeneous freezing is a volume-proportional process and that surface nucleation might only be important, if at all, for much smaller droplets

Patron Demand Deposit Account and Regional Patronage Financing Activities of Agribusiness Cooperatives

This paper investigates agribusiness cooperatives' reliance on patron demand deposit accounts (PDDAs) and regional patronage as sources of capital. Approximately 13% of cooperatives carry PDDAs, typically fruit cooperatives, of which over one-half have no financial protection against large unexpected withdrawals. Cooperatives with PDDAs must be concerned with potential legal conflicts regarding the handling of these accounts, as evidenced by a U.S. Supreme Court case classifying PDDAs as securities. Supply cooperatives are most likely to show investment in other cooperatives as a high percentage of total assets, which could generate insolvency issues for locals.cooperative finance, patron demand deposit accounts, regional patronage., Agricultural Finance, Agribusiness,

Experimental quantification of contact freezing in an electrodynamic balance

Heterogeneous nucleation of ice in a supercooled water droplet induced by external contact with a dry aerosol particle has long been known to be more effective than freezing induced by the same nucleus immersed in the droplet. However, the experimental quantification of contact freezing is challenging. Here we report an experimental method to determine the temperature-dependent ice nucleation probability of size-selected aerosol particles. The method is based on the suspension of supercooled charged water droplets in a laminar flow of air containing aerosol particles as contact freezing nuclei. The rate of droplet–particle collisions is calculated numerically with account for Coulomb attraction, drag force and induced dipole interaction between charged droplet and aerosol particles. The calculation is verified by direct counting of aerosol particles collected by a levitated droplet. By repeating the experiment on individual droplets for a sufficient number of times, we are able to reproduce the statistical freezing behavior of a large ensemble of supercooled droplets and measure the average rate of freezing events. The freezing rate is equal to the product of the droplet–particle collision rate and the probability of freezing on a single contact, the latter being a function of temperature, size and composition of the contact ice nuclei. Based on these observations, we show that for the types of particles investigated so far, contact freezing is the dominating freezing mechanism on the timescale of our experiment

PHIPS-HALO: The airborne Particle Habit Imaging and Polar Scattering probe-Part 1: Design and operation

This is an Open Access article distributed under the terms ofthe Creative Commons Attribution 3.0 License https://creativecommons.org/licenses/by/3.0/The number and shape of ice crystals present in mixed-phase and ice clouds influence the radiation properties, precipitation occurrence and lifetime of these clouds. Since clouds play a major role in the climate system, influencing the energy budget by scattering sunlight and absorbing heat radiation from the earth, it is necessary to investigate the optical and microphysical properties of cloud particles particularly in situ. The relationship between the microphysics and the single scattering properties of cloud particles is usually obtained by modelling the optical scattering properties from in situ measurements of ice crystal size distributions. The measured size distribution and the assumed particle shape might be erroneous in case of non-spherical ice particles. There is a demand to obtain both information correspondently and simultaneously for individual cloud particles in their natural environment. For evaluating the average scattering phase function as a function of ice particle habit and crystal complexity, in situ measurements are required. To this end we have developed a novel airborne optical sensor (PHIPS-HALO) to measure the optical properties and the corresponding microphysical parameters of individual cloud particles simultaneously. PHIPS-HALO has been tested in the AIDA cloud simulation chamber and deployed in mountain stations as well as research aircraft (HALO and Polar 6). It is a successive version of the laboratory prototype instrument PHIPS-AIDA. In this paper we present the detailed design of PHIPS-HALO, including the detection mechanism, optical design, mechanical construction and aerodynamic characterization.Final Published versio

Unravelling the microphysics of polar mesospheric cloud formation

Polar mesospheric clouds are the highest water ice clouds occurring in the terrestrial atmosphere. They form in the polar summer mesopause, the coldest region in the atmosphere. It has long been assumed that these clouds form by heterogeneous nucleation on meteoric smoke particles which are the remnants of material ablated from meteoroids in the upper atmosphere. However, until now little was known about the properties of these nanometre-sized particles and application of the classical theory for heterogeneous ice nucleation was impacted by large uncertainties. In this work, we performed laboratory measurements on the heterogeneous ice formation process at mesopause conditions on small (r=1 to 3&thinsp;nm) iron silicate nanoparticles serving as meteoric smoke analogues. We observe that ice growth on these particles sets in for saturation ratios with respect to hexagonal ice below Sh=50, a value that is commonly exceeded during the polar mesospheric cloud season, affirming meteoric smoke particles as likely nuclei for heterogeneous ice formation in mesospheric clouds. We present a simple ice-activation model based on the Kelvin–Thomson equation that takes into account the water coverage of iron silicates of various compositions. The activation model reproduces the experimental data very well using bulk properties of compact amorphous solid water. This is in line with the finding from our previous study that ice formation on iron silicate nanoparticles occurs by condensation of amorphous solid water rather than by nucleation of crystalline ice at mesopause conditions. Using the activation model, we also show that for iron silicate particles with dry radius larger than r=0.6&thinsp;nm the nanoparticle charge has no significant effect on the ice-activation threshold.</p

Optical properties of meteoric smoke analogues

Accurate determination of the optical properties of analogues for meteoric smoke particles (MSPs), which are thought to be composed of iron-rich oxides or silicates, is important for their observation and characterization in the atmosphere. In this study, a photochemical aerosol flow system (PAFS) has been used to measure the optical extinction of iron oxide MSP analogues in the wavelength range 325–675 nm. The particles were made photochemically and agglomerate into fractal-like particles with sizes on the order of 100 nm. Analysis using transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX) and electron energy loss spectroscopy (EELS) suggested the particles were most likely maghemite-like (γ-Fe2O3) in composition, though a magnetite-like composition could not be completely ruled out. Assuming a maghemite-like composition, the optical extinction coefficients measured using the PAFS were combined with maghemite absorption coefficients measured using a complementary experimental system (the MICE-TRAPS) to derive complex refractive indices that reproduce both the measured absorption and extinction

Avaliação da expansão da cana-de-açúcar segundo os critérios de sustentabilidade da diretiva europeia 2009/28/CE: estudo de caso de Rancharia - SP.

Resumo: O interesse mundial na produção e consumo de biocombustíveis, principalmente o etanol, vem crescendo desde a virada do século. De acordo com os critérios de sustentabilidade da Diretiva Europeia 2009/28/CE (DE), biocombustíveis não devem ser produzidos a partir de matérias-primas provenientes de terrenos ricos em biodiversidade. Nesse contexto, o monitoramento da expansão da cana torna-se fundamental e as imagens de sensoriamento remoto apresentam potencial para este tipo de análise, pois possuem capacidade para identificar sobre quais usos da terra que esta cultura tem se expandido. Rancharia-SP, foi a cidade escolhida para a análise expansão da cana, porque de acordo com o projeto Canasat do Instituto Nacional de Pesquisas Espaciais (INPE), entre as safras de 2007 e 2013, a área plantada aumentou aproximadamente 200%. Foi então realizada a classificação supervisionada das imagens de satélite, pelo método de máxima verossimilhança, em dois períodos: 2007 (antes da DE) e 2014 (depois da DE). De acordo com os dados obtidos, a expansão da cana-de-açúcar ocorreu principalmente sobre áreas onde antes eram pastagens, 34 mil ha (99%) e solo exposto, 322,71 ha (1%), e não expandiu para áreas de vegetação natural, ou seja, houve o cumprimento da Diretiva Europeia

Identification of gaps in sugarcane plantations using UAV images.

The objective of this study is to present a methodology for the detection and quantification of gaps formed during planting or growing of sugarcane crops. The use of UAV images for precision agriculture is relevant because it brings new possibilities for improving crop's productivity by feeding the producer with highly accurate data about the crop status

Drying of a Microdroplet of Water Suspension of Nanoparticles: from Surface Aggregates to Microcrystal

The method of formation of nanoparticle aggregates such as high-coverage spherical shells of microspheres or 3-D micro crystals grown in the geometry unaffected by a substrate is described. In the reported experiment, the evaporation of single levitated water droplet containing 200 nm diameter polystyrene spheres was studied. Successive stages of the drying process were discussed by analyzing the intensity of light elastically scattered by the evaporating droplet. The numerically simulated self-assembly coincides nicely with the observed morphologies resulting from transformation of a droplet of suspension into a solid microcrystal via kinetically driven self-assembly of nanostructures.Comment: 5 pages, 6 figure