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J. Lorente, A. Redañ, and X. De Cabo

Abstract

From a dataset of spectral distribution of global and disuse solar irradiances measured in Barcelona during the last three years, the influence of turbidity caused by urban aerosol on spectral composition of solar radiation and transmissivity of urban atmosphere has been determined for cloudless conditions. The effect of urban aerosol is remarkable, mainly in the ultraviolet (UV) part of the spectrum, where attenuation of global irradiance surpasses 25% on very polluted days. The increases in diffuse UV irradiance caused by aerosols ranges in the interval 4%–50%, while this increase ranges from 20% to 250% for the whole solar spectrum. Comparison of spectral irradiance observed for different turbidities with various models shows a good agreement, mainly in the UV and visible spectral regions. Erythemally effective irradiance, that is, a biological measures of the sunburning power of solar radiation, has also been calculated for different aerosol concentrations, giving values in the range of 0.15–0.25 W m−2 in the UV region but insignificant values for the rest of the solar spectrum.

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G. Delgado, Luiz A. T. Machado, Carlos F. Angelis, Marcus J. Bottino, Á. Redaño, J. Lorente, L. Gimeno, and R. Nieto

Abstract

This paper discusses the basis for a new rainfall estimation method using geostationary infrared and visible data. The precipitation radar on board the Tropical Rainfall Measuring Mission satellite is used to train the algorithm presented (which is the basis of the estimation method) and the further intercomparison. The algorithm uses daily Geostationary Operational Environmental Satellite infrared–visible (IR–VIS) cloud classifications together with radiative and evolution properties of clouds over the life cycle of mesoscale convective systems (MCSs) in different brightness temperature (Tb) ranges. Despite recognition of the importance of the relationship between the life cycle of MCSs and the rainfall rate they produce, this relationship has not previously been quantified precisely. An empirical relationship is found between the characteristics that describe the MCSs’ life cycle and the magnitude of rainfall rate they produce. Numerous earlier studies focus on this subject using cloud-patch or pixel-based techniques; this work combines the two techniques. The algorithm performs reasonably well in the case of convective systems and also for stratiform clouds, although it tends to overestimate rainfall rates. Despite only using satellite information to initialize the algorithm, satisfactory results were obtained relative to the hydroestimator technique, which in addition to the IR information uses extra satellite data such as moisture and orographic corrections. This shows that the use of IR–VIS cloud classification and MCS properties provides a robust basis for creating a future estimation method incorporating humidity Eta field outputs for a moisture correction, digital elevation models combined with low-level moisture advection for an orographic correction, and a nighttime cloud classification.

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S. Jerez, R. M. Trigo, S. M. Vicente-Serrano, D. Pozo-Vázquez, R. Lorente-Plazas, J. Lorenzo-Lacruz, F. Santos-Alamillos, and J. P. Montávez

Abstract

Europe is investing considerably in renewable energies for a sustainable future, with both Iberian countries (Portugal and Spain) promoting significantly new hydropower, wind, and solar plants. The climate variability in this area is highly controlled by just a few large-scale teleconnection modes. However, the relationship between these modes and the renewable climate-dependent energy resources has not yet been established in detail. The objective of this study is to evaluate the impact of the North Atlantic Oscillation (NAO) on the interannual variability of the main and primary renewable energy resources in Iberia. This is achieved through a holistic assessment that is based on a 10-km-resolution climate simulation spanning the period 1959–2007 that provides physically consistent data of the various magnitudes involved. A monthly analysis for the extended winter (October–March) months shows that negative NAO phases enhance wind speeds (10%–15%) and, thereby, wind power (estimated around 30% at typical wind-turbine altitudes) and hydropower resources (with changes in precipitation exceeding 100% and implying prolonged responses in reservoir storage and release throughout the year), while diminishing the solar potential (10%–20%). Opposite signals were also sporadically identified, being well explained when taking into account the orography and the prevailing wind direction during both NAO phases. An additional analysis using real wind, hydropower, and solar power generation data further confirms the strong signature of the NAO.

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José A. Martínez-Lozano, Maria P. Utrillas, Roberto Pedrós, Fernando Tena, Juan P. Díaz, Francisco J. Expósito, Jerónimo Lorente, Xavier de Cabo, Victoria Cachorro, Ricardo Vergaz, and Virgilio Carreño

Abstract

This paper presents the results of the analysis of the spectral, global, and direct solar irradiance measurements in the visible range (400–700 nm) that were made in the framework of the first Iberian UV–visible (VIS) instruments intercomparison. The instruments used in this spectral range were four spectroradiometers: three Licor 1800s equipped with different receiver optics and one Optronic 754. For the direct solar irradiance measurements the spectroradiometers were equipped with collimators with different fields of view. Parallel studies have been carried out with the data given by the spectroradiometers with their original calibration file and with the same data that is corrected, following in situ calibration of the instruments using a laboratory reference lamp. To compare the series of spectral data the relative values of mean absolute deviation (MAD) and root-mean-square deviation (rmsd) have been used. The results obtained from the measurements of global irradiance show that the Licor 1800s presented very significant differences at the beginning and at the end of the day due to the deviation from ideal cosine response of the collection optics (i.e., cosine errors). This forced the analysis to be limited to the measurements corresponding to solar elevations higher than 30°. For this solar elevation range, the results of the intercomparison between the Licor instruments, before their in situ calibration, showed differences of about 5% in the visible range. The results from the measurements of direct irradiance show that, if correction factors are considered, these deviations are reduced to 3%, and when the Licors are compared with the Optronic, the deviations are less than 2%.

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