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Thirty Years of Atmospheric Extinction from Telescopes of the North Atlantic Canary Archipelago

2026-05-01T14:15:00Z

Título : Thirty Years of Atmospheric Extinction from Telescopes of the North Atlantic Canary Archipelago Autor : Laken, Benjamin A.; Parviainen, Hannu; García Gil, Alejandro Manuel; Muñoz Tuñón, Casiana; Varela, Antonia María; Fernández-Acosta, Sergio; Pallé, Pere Resumen : This study examines 30 years of atmospheric extinction, τ, obtained from both stellar and solar telescope measurements, at ~2.4 km MSL, from the North Atlantic Canary Archipelago—an island chain located at approximately 28°N, around 100 km from the west coast of Africa. Data from three AERONET monitors, located at varying heights on one of the main islands, were also used, although these are only available over a shorter (<10 yr) period. The Canary Archipelago is regularly affected by dust intrusions into the local atmosphere as they intersect one of the primary export pathways of mineral dust from the Sahara. The τ of “baseline” and “dust influenced” conditions were statistically distinguished by fitting normal-gamma mixture distributions to the observations using Markov chain Monte Carlo methods, and then the seasonal and long-term characteristics of these data were examined. The telescope data show that baseline conditions are usually stable at τ < 0.1 (except during periods influenced by volcanic aerosols) and indicate the existence of a low-amplitude () seasonal variation. During dust-influenced conditions, τ regularly reaches values of a factor of 2–6 times higher than normal. The majority of dust intrusions take place during the months of July and August, when they may occur 44 ± 15% of the time, predominantly at high altitudes (with ~94.3 ± 1.6% of intrusions occurring ≥ 2.4 km), whereas during the months of November–May, dust intrusions occur far less frequently (~19 ± 7%) and are more common at lower altitudes—with intrusions at <2.4 km comprising ~ 79.5 ± 3.2% of all outbreaks. Year-to-year variations in the frequency of dust-influenced conditions (of ~9%) were found but no long-term trend over the observed 30-yr period.

Characterization of the instrument temperature dependence of Brewer total ozone column measurements [Discussion paper]

2026-04-30T23:19:17Z

Título : Characterization of the instrument temperature dependence of Brewer total ozone column measurements [Discussion paper] Autor : Berjón, Alberto; Redondas, Alberto; Sildoja, Meelis-Mait; Nevas, Saulius; Wilson, Keith M.; León-Luis, Sergio Fabián; el-Gawhary‏, Omar‏; Fountoulakis, Ilias Resumen : The instrumental temperature correction to be applied to the ozone measurements by the Brewer spectrophotometers is derived from measurements of the irradiance from an internal halogen lamp in the instrument. These characterisations of the Brewer instruments can be carried out within a thermal chamber, varying the temperature from -5◦C to +45◦C, or during field measurements, making use of the natural change in ambient temperature. However, the internal light source used to determine 5 the thermal sensitivity of the instrument could be affected in both methods by the temperature variations as well, which may affect the determination of the temperature coefficients. In order to validate the standard procedures for determining Brewer’s temperature coefficients, two independent experiments using both external light sources and the internal lamps have been performed within the ATMOZ Project. The results clearly show that the traditional methodology based on the internal lamps is not affected by possible temperature effects on the internal lamps. The three methodologies yielded equivalents results, with differences in total ozone column below 0.08% for a mean diurnal temperature variation of 10◦ 10 C.

Wind Forecasting Based on the HARMONIE Model and Adaptive Finite Elements

2026-05-01T15:59:07Z

Título : Wind Forecasting Based on the HARMONIE Model and Adaptive Finite Elements Autor : Oliver, Albert; Rodríguez, Eduardo; Escobar, José María; Montero García, Gustavo; Hortal Reymundo, Mariano; Calvo Sánchez, Francisco Javier; Cascón, José Manuel; Montenegro Armas, Rafael Resumen : In this paper, we introduce a new method for wind field forecasting over complex terrain. The main idea is to use the predictions of the HARMONIE meso-scale model as the input data for an adaptive finite element mass-consistent wind model. The HARMONIE results (obtained with a maximum resolution of about 1 km) are refined in a local scale (about a few metres). An interface between both models is implemented in such a way that the initial wind field is obtained by a suitable interpolation of the HARMONIE results. Genetic algorithms are used to calibrate some parameters of the local wind field model in accordance to the HARMONIE data. In addition, measured data are considered to improve the reliability of the simulations. An automatic tetrahedral mesh generator, based on the meccano method, is applied to adapt the discretization to complex terrains. The main characteristic of the framework is a minimal user intervention. The final goal is to validate our model in several realistic applications on Gran Canaria island, Spain, with some experimental data obtained by the AEMET in their meteorological stations.

Remote sensing of lunar aureole with a sky camera: Adding information in the nocturnal retrieval of aerosol properties with GRASP code

2026-04-30T23:19:21Z

Título : Remote sensing of lunar aureole with a sky camera: Adding information in the nocturnal retrieval of aerosol properties with GRASP code Autor : Román, Roberto; Torres, Benjamín; Fuertes, David; Cachorro, Victoria E.; Dubovik, Oleg; Toledano, Carlos; Cazorla, Alberto; Barreto Velasco, África; Bosch, Juan Luis; Lapyonok, Tatsiana; González, Ramiro; Goloub, Philippe; Perrone, Maria Rita; Olmo Reyes, Francisco José; Frutos Baraja, Ángel Máximo de; Alados Arboledas, Lucas Resumen : The use of sky cameras for nocturnal aerosol characterization is discussed in this study. Two sky cameras are configured to take High Dynamic Range (HDR) images at Granada and Valladolid (Spain). Some properties of the cameras, like effective wavelengths, sky coordinates of each pixel and pixel sensitivity, are characterized. After that, normalized camera radiances at lunar almucantar points (up to 20° in azimuth from the Moon) are obtained at three effective wavelengths from the HDR images. These normalized radiances are compared in different case studies to simulations fed with AERONET aerosol information, giving satisfactory results. The obtained uncertainty of normalized camera radiances is around 10% at 533 nm and 608 nm and 14% for 469 nm. Normalized camera radiances and six spectral aerosol optical depth values (obtained from lunar photometry) are used as input in GRASP code (Generalized Retrieval of Aerosol and Surface Properties) to retrieve aerosol properties for a dust episode over Valladolid. The retrieved aerosol properties (refractive indices, fraction of spherical particles and size distribution parameters) are in agreement with the nearest diurnal AERONET products. The calculated GRASP retrieval at night time shows an increase in coarse mode concentration along the night, while fine mode properties remained constant.