111 research outputs found
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 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 nm the nanoparticle charge has no significant
effect on the ice-activation threshold.</p
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
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
The impact of solar radiation on polar mesospheric ice particle formation
Mean temperatures in the polar summer mesopause can drop to 130 K. The low
temperatures in combination with water vapor mixing ratios of a few parts per
million give rise to the formation of ice particles. These ice particles may
be observed as polar mesospheric clouds. Mesospheric ice cloud formation is
believed to initiate heterogeneously on small aerosol particles (r < 2 nm) composed of recondensed meteoric material, so-called meteoric
smoke particles (MSPs). Recently, we investigated the ice activation and
growth behavior of MSP analogues under realistic mesopause conditions. Based
on these measurements we presented a new activation model which largely
reduced the uncertainties in describing ice particle formation. However, this
activation model neglected the possibility that MSPs heat up in the
low-density mesopause due to absorption of solar and terrestrial irradiation.
Radiative heating of the particles may severely reduce their ice formation
ability. In this study we expose MSP analogues (Fe2O3 and
FexSi1 − xO3) to realistic mesopause
temperatures and water vapor concentrations and investigate particle warming
under the influence of variable intensities of visible light (405, 488, and
660 nm). We show that Mie theory calculations using refractive indices of
bulk material from the literature combined with an equilibrium temperature
model presented in this work predict the particle warming very well.
Additionally, we confirm that the absorption efficiency increases with the
iron content of the MSP material. We apply our findings to mesopause
conditions and conclude that the impact of solar and terrestrial radiation on
ice particle formation is significantly lower than previously assumed.</p
Cenário agroenergético da cana-de-açúcar em São Paulo: uma avaliação da sensibilidade socioeconômica e ambiental utilizando sistema de informação geográfica (SIG).
Resumo: Tendo em vista o crescente interesse mundial no consumo de biocombustíveis e as incertezas quanto a seus reais benefícios, o objetivo deste trabalho foi avaliar, com auxílio de sistema de informações geográficas (SIG), a sensibilidade das áreas utilizadas para a produção de cana no estado de São Paulo, integrando indicadores ambientais e socioeconômicos. A metodologia consistiu em classificar os dados (porcentagem de empregos na cana em relação à agricultura; renda média do trabalhador na cana; anos de estudo dos trabalhadores na produção de cana; trabalho infantil; balanço quali-quantitativo; área de proteção ambiental; declividade; zoneamento agroecológico da cana; aptidão agrícola) em três graus de sensibilidade: alta, média e baixa. Foi então realizada álgebra de mapas cuja regra adotada para analisar a sensibilidade foi: se houvesse alta sensibilidade em no mínimo um nível de informação, a área seria classificada como de alta sensibilidade. De acordo com o mapa final, 58% da cana do estado, 3.414.772 ha, está plantada em áreas de alta sensibilidade. Muitos são os fatores que devem ser aprimorados para que o protagonismo da cultura no estado possa ser revertido em ampliação da agroenergia na matriz ou em favor de uma matriz enérgica sustentável
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