A. M. de Frutos

Aerosols in polar regions: A historical overview based on optical depth and in situ observations

Large sets of filtered actinometer, filtered pyrheliometer and Sun photometer measurements have been carried out over the past 30 years by various groups at different Arctic and Antarctic sites and ...

Determination of the Angstrom turbidity parameters

We have analyzed the dependence of the Angstrom turbidity parameters on wavelength throughout the visible range by three different methods. We have obtained significant results about the ability of these parameters to represent the turbidity of the atmosphere. An important variation of these coefficients with the wavelength is shown, depending on the method used and the spectral resolution of the data. The log-log plot of aerosol optical thickness vs wavelength appears as an adequate method of obtaining the Angstrom parameters to represent the turbidity of the atmosphere and to model the effect of aerosols on solar radiation.

The strongest desert dust intrusion mixed with smoke over the Iberian Peninsula registered with Sun photometry

[1] We present the analysis of the strongest North African desert dust (DD) intrusion that occurred over the Iberian Peninsula (IP) during the last decade, as registered by modern remote sensing techniques like Sun photometry. This event took place from 22 July to 3 August 2004. The most relevant features of this exceptional event, originated over the Saharan desert, were its great intensity and duration. We focus on the columnar aerosol properties measured by the AERONET-Cimel photometers at El Arenosillo (southwest) and Palencia (north-center) stations. Aerosol optical depth (AOD) reached a maximum of 2.7 at El Arenosillo during 22 July and 1.3 at Palencia on 23 July, with the Ansgtrom exponent values near zero during the AOD peaks. In addition, PM10 concentration levels are also reported at various sites of the IP in order to establish the impact of this intrusion, reaching daily values as high as 200 μg/m 3 and peaks near 600 μg/m 3 in an hourly basis. The interest of this special event is increased because of the mixing with smoke particles from concurrent forest fires in the IP. Features of the columnar volume particle size distribution and derived microphysical parameters, the single scattering albedo, and a reliable estimation of the radiative forcing under these extreme conditions are also reported. Complementary information, as air mass back trajectories, synoptic charts, images, and AOD maps of satellite sensors (SeaWIFS, MODIS) together with NAAPS prognostic model, is used in the analysis in order to draw a detailed scenario of this dust-smoke event over the IP.

Experimental study of laser-induced plasma in welding conditions with continuous CO2 laser

Laser‐induced plasmas obtained during a welding process have been studied. Spectroscopic diagnostics and an integrating sphere collecting the reflected CO2 light are the principal diagnostics used in order to determine the spatial variations of the microscopic parameters such as electron density and temperature, and the energy absorption during this process. For several experimental processing conditions of shielding gases, the main perturbing effects such as absorption and refraction of the CO2 laser radiation are quantified. Several possibilities for reducing these perturbing effects are then discussed.

Fitting ångström's formula to spectrally resolved aerosol optical thickness

Abstract The ability of the Angstrom equation to represent the spectral behavior of the aerosol optical thickness is analyzed for various atmospheric turbidity conditions. This analysis is carried out by means of the spectral values of the aerosol optical thickness obtained by experimental spectral direct solar irradiance data.

Holographic filter that transforms a Gaussian into a uniform beam

A simple method of constructing a holographic filter is described which transforms a Gaussian into a uniform beam and conserves 30% of the beam power.

The influence of ångström parameters on calculated direct solar spectral irradiances at high turbidity

Abstract This work analyzes the influence of angstrom parameters on modeled spectral solar irradiance data. The angstrom parameters are obtained in the same way as in the Volz method but using continuous record of spectral direct solar irradiance measures in the 400–1000 nm spectral range. Different pairs of α-β values are obtained depending on the two selected wavelengths. The comparison between the calculated irradiance data with these different α-β pairs and experimental data show important differences that may be taken into account in irradiance models.

A revised study of the validity of the general junge relationship at solar wavelengths: Application to vertical atmospheric aerosol layer studies

Abstract The relationship between the Junge aerosol size parameter and the α Angstrom turbidity parameter, known as the Junge relationship v = α +2, is commonly applied in aerosol studies. However, this relationship involves some approximations, therefore here the v − α relationship is established generally. A thorough analysis has been carried out taking into account the sensitivity and features of the Junge function on particle radius and wavelengths by means of the volume extinction coefficient and its cumulative values. Hence, the relationship v − α is analysed to (a) extend its validity to solar wavelengths; (b) incorporate new particle radius intervals [r 1 −r 2 ] and (c) analyse the influence of the particle refractive index. As a consequence the applicability and limitations of the linear Junge relationship v = α +2 become apparent. The results show that the relationship between the v and the α parameters in the visible range can extend its validity in the whole solar range if the volume extinction coefficient shows a linear behaviour throughout this range. Curvatures of the extinction coefficient for particle size distribution functions with an upper limit of 1 μm or lower limit of 0.1 μm have been observed. However, due to these features dependence on the Junge values, these are irrelevant when they are applied to real cases of atmospheric turbidity.

Comparison between various models of solar spectral irradiance and experimental data

Three models of spectral direct irradiance of the sun at the ground are compared with experimental spectral measurements. Satisfactory agreement is obtained although their behavior is quite different mainly in the absorption bands. The turbidity parameters required by the model are obtained from the measured data and the water vapor by simultaneous radiosondage.

Absorption by oxygen and water vapor in the real atmosphere

Unexpected absorption in the real atmosphere in the window from 840 to 890 nm has been clearly observed through measurements of direct solar spectral irradiance under clear, cloud-free skies. This absorption is not predicted by the known theoretical models. The cause of this apparent absorption may be due to the presence of high thin nonvisible cirrus clouds. A quantitative evaluation of this absorption and an improvement of oxygen absorption coefficients has been carried out after a comparison of more than seventy experimental spectra. Moreover, it is necessary to take into account the different behavior of modeled and experimental data at low and high air masses.