Search results for "Angstrom"
showing 10 items of 36 documents
Validation of a very simple model for computing global solar radiation in the European, African, Asian and North American areas
1990
Abstract In a previous paper Coppolino has proposed a very simple model for predicting the monthly mean daily global solar radiation G (MJm −2 day −1 ) at any Italian location using as input only the sunshine duration s (hours) and the noon altitude of the sun on the 15th of the month h n (degrees). The correlation suggested is G = 7.8 s 0.5 (sin h n ) 1.15 . Herein the validity of this model is verified by extending its application to dat from 24 stations displaced at various latitudes, altitudes above sea level and geographical situations in the European, African, Asian and North American areas. Furthermore the validity of this model to fit the data of the tested stations is compared with…
Mesoscopic organization in ionic liquids.
2017
We discuss some published results and provide new observations concerning the high level of structural complexity that lies behind the nanoscale correlations in ionic liquids (ILs) and their mixtures with molecular liquids. It turns out that this organization is a consequence of the hierarchical construction on both spatial (from ångström to several nanometer) and temporal (from fraction of picosecond to hundreds of nanosecond) scales, which requires joint use of experimental and computational tools. © 2017, Springer International Publishing Switzerland.
Assessment and application of MODIS ocean and land algorithms for the characterization of aerosol properties over a Mediterranean coastal site
2015
Abstract The aerosol optical depth (AOD) and Angstrom exponent (α) obtained from MODIS Terra and Aqua over the coastal urban site of Burjassot (Spain) during the period 2002–2011 have been compared with retrievals from AERONET (AErosol RObotic NETwork) and ESR (European Skynet Radiometers) in order to investigate the performance of MODIS algorithms over land and ocean, respectively. The comparison of the MODIS aerosol products C051 over both land and ocean has been performed for a window size of 50 km × 50 km centred on the monitoring site. The correlation coefficients obtained from the comparison of the AOD from MODIS with that from ground-based measurements are 0.85 and 0.87 over land for…
Long term analysis of the columnar and surface aerosol relationship at an urban European coastal site
2017
Abstract Simultaneous PM2.5, PM10 and columnar (ground and satellite based) AOD measurements have been analyzed at Burjassot site in the metropolitan area of Valencia (Spain) during the period 2007–2016. The site is representative of a south European city in the Western Mediterranean coastal area, influenced by local urban pollution but also from frequent Saharan dust events. First, multiannual statistics were performed to characterize the main aerosol burden characteristics. The averages and standard deviations resulted 18 ± 9 μg m−3, 25 ± 19 μg m−3, 0.15 ± 0.11, 0.23 ± 0.17, 0.19 ± 0.15 and 1.2 ± 0.3 for PM2.5, PM10, AERONET AOD, MODIS Terra AOD, MODIS Aqua AOD, and AERONET Angstrom expon…
In-situ integrating nephelometer measurements of the scattering properties of atmospheric aerosols at an urban coastal site in western Mediterranean
2012
Abstract Measurements of aerosol scattering properties obtained during the period from March 2006 to December 2010 at Valencia (Spain) have been analyzed. The total aerosol scattering (σsp) and backscattering (σbsp) coefficients were measured using a TSI Model 3563 three-wavelength integrating nephelometer. From the measurements of σsp and σbsp, it was possible to determine also the scattering Angstrom exponent (αs). For the entire measurement period, the mean values (±standard deviation) at 550 nm are: 80 ± 50 Mm−1 for σsp; 8 ± 5 Mm−1 for σbsp; and 1.6 ± 0.3 for αs. These results indicate a moderate polluted atmosphere characterized by fine particles. The daily variation for all seasons sh…
Estimation of daily average values of the Ångström turbidity coefficient β using a Corrected Yang Hybrid Model
2013
This paper aims to test a method for estimating daily values of atmospheric turbidity from non-specialized data, such as those obtained from agro-meteorological stations. This method allows estimating the spatial and temporal evolution of aerosols concentration in more places than just those in which direct measurements are available. The method is based on the Corrected Yang Hybrid Model (CYHM). The data used in the determination of errors between measured and estimated values of the daily Angstrom turbidity coefficient β were recorded in Valencia, Spain, during 2009 and 2011. These data were global solar irradiance, direct solar irradiance, temperature, relative humidity and Aerosol Optic…
The parameterisation of the atmospheric aerosol optical depth using the Ångström power law
1998
Abstract We have analysed the ability of the Angstrom power law to model the spectral aerosol optical depth, τaλ, for the 400–670 nm band, obtained from spectral direct irradiance measurements at normal incidence. The spectra were registered at ground level in Valencia, Spain, using a Li-cor 1800 spectroradiometer. The results obtained showed that the fitting method that introduces lower errors in the determination of the Angstrom power law coefficients is to adjust directly the spectral experimental data. In this way the errors obtained for the turbidity coefficient, β, were about 0.004 and for the wavelength exponent, α, 0.07. The correlation coefficient was always greater than 0.95. Thes…
Blue Moon: Is This a Property of Background Aerosol?
2010
Stellar extinction measurements made at three astronomical observatories showed that on ~50% of the nights the extinction due to aerosol light scattering increased rather than decreased with increasing wavelength (anomalous extinction) for wavelengths close to 500 nm. This extinction behavior is analyzed in this paper and limits are established for the aerosol characteristics necessary for this phenomenon to exist, including geometric standard deviations, imaginary part of refractive index, mean radius, and gaseous NO(2).
VLT/Flames observations of the star forming region NGC 6530
2006
Mechanisms regulating the evolution of pre-main sequence stars can be understood by studying stellar properties such as rotation, disk accretion, internal mixing and binarity. To investigate such properties, we studied a sample of 332 candidate members of the massive and populous star forming region NGC 6530. We want to select cluster members by using different membership criteria,to study the properties of pre-main sequence stars with or without circumstellar disks. We use intermediate resolution spectra including the Li I 6707.8 Angstroms line to derive radial and rotational velocities, binarity and to measure the Equivalent Width of the lithium line; these results are combined with X-ray…
Calculations and measurements of the spectral radiance of the solar aureole
1968
The application of the theory of primary scattering to describe and interpret the spectral distribution of the sky radiance is discussed. It is shown that within the solar aureole the influence of the scattering of higher order can be neglected. Theoretical calculations of the spectral distribution of the sky radiance, carried out by Bullrich et al . (1965) based on an exponential aerosol size distribution with an upper limiting particle radius r = 10 ?, have been extended to r = 150 ?. The detailed study of the influence of these “giant” particles revealed that aerosol particles of r >30 ? have no effect on the sky radiation any more. Representative measurements taken at Mainz, Germany, at…