Application of SPCTRAL2 parametric model in estimating spectral solar irradiances over polluted Athens atmosphere

Results obtained using SPCTRAL2 parametric model for the polluted urban atmosphere of Athens, Greece, were analysed and compared with ground level experimental spectral solar irradiance measurements and spectrally integrated solar irradiances in two discrete narrow bands, ultraviolet and visible. For the aerosol characterization, the aerosol optical depth evaluated at 500 nm was used as the basic input parameter. The algorithm used seems to reproduce the experimental solar spectral irradiances adequately depending on the aerosol model used. The results obtained have been explained through mean bias and root mean square statistical deviations and the resultant influence of the aerosol volume spectra. © 2003 Elsevier Ltd. All rights reserved

Wind statistics for coastal stations in Cyprus

A statistical analysis of wind speed and direction data for five selected meteorological stations at the Cyprus coast, is carried out in this study. Daily, monthly and annual variations of wind speed are established. The Weibull distribution statistics of the sites are also determined. In addition, an attempt is made to find the sea-breeze circulation effects in the same wind data. The wind statistics obtained are expected to serve as a validation test for wind energy applications, mainly along the southeastern coastline

Comparative study of various correlations in estimating hourly diffuse fraction of global solar radiation

Proper design and performance predictions of solar energy systems require accurate information on the availability of solar radiation. The diffuse-to-global solar radiation correlation, originally developed by Liu and Jordan, has been extensively used as the technique providing accurate results, although it is latitude dependent. Thus, in the present study, empirical correlations of this type were developed to establish a relationship between the hourly diffuse fraction (kd) and the hourly clearness index (kt) using hourly global and diffuse irradiation measurements on a horizontal surface performed at Athalassa, Cyprus. The proposed correlations were compared against 10 models available in the literature in terms of the widely used statistical indicators, rmse, mbe and t test. From this analysis, it can be concluded that the proposed yearly correlation predicts diffuse values accurately, whereas all candidate models examined appear to be location-independent for diffuse irradiation predictions. © 2005 Elsevier Ltd. All rights reserved

The dependence of global and diffuse PAR radiation components on sky conditions at Athens, Greece

The interrelationship between broadband solar components, global (RS) and diffuse (Rd) and the photosynthetic photon flux density components, global (QP) and diffuse (QPd), is investigated using a 2-year data archive obtained at Athens, Greece. These data are used to determine temporal variability of the ratios (QP/RS) and (QPd/Rd) and their dependence on sky conditions. The seasonal variation of the ratios obtained from hourly data ranges from 2.006 ± 0.032 (winter) to 1.989 ± 0.028 μmol J-1 (summer) with an annual mean of 1.995 ± 0.032 μmol J-1 for (QP/RS) and from 2.298 ± 0.27 (winter) to 2.538 ± 0.22 μmol J-1 (summer) with an annual mean of 2.434 ± 0.26 μmol J-1 for (QPd/Rd). The hourly ratio (QP/RS) increased from 1.982 ± 0.025 to 2.106 ± 0.029 μmol J-1 as sky conditions changed from clear to overcast; whereas the ratio (QPd/Rd) decreased from 2.556 ± 0.27 to 2.422 ± 0.24 μmol J-1 as sky conditions changed from clear to overcast skies. The seasonal daily ratio patterns are presented and discussed through clearness index kt (the ratio of the global-to-extraterrestrial solar radiation). Finally, the relationship between the spectral diffuse fraction kdP (the ratio of diffuse PAR-to-global PAR radiation) and the clearness index ktP (the ratio of global PAR-to-extraterrestrial solar PAR) is established for the Athens atmosphere. © 2007 Elsevier B.V. All rights reserved

Global photosynthetically active radiation and its relationship with global solar radiation in the Eastern Mediterranean basin

The relationship between global photosynthetically active radiation (PAR) and global solar radiation is studied with a 2-year data archive of hourly values HPAR and HSW of these irradiances obtained at Athalassa, Cyprus. These data are used to determine the temporal variability of HPAR and its dependence on sky conditions. The seasonal variation of the ratio HPAR/HSW obtained from daily data ranges from 0.456 (during summer) to 0.451 (during winter) with an annual mean value of 0.454. The ratio increases from 0.454 to 0.467 (daily values) or from 0.460 to 0.501 (hourly values), as sky conditions change from clear to overcast. Finally, the effect of aerosol content on the HPAR/HSW ratio is found to incur substantial changes in the PAR fraction

Solar global UV (280-380 nm) radiation and its relationship with solar global radiation measured on the island of Cyprus

We report the first observations of solar global UV (280-380 nm) radiation on the island of Cyprus obtained during an ongoing joint research project between the University of Athens and the Meteorological Service of Cyprus. Hourly global UV (Guv) and global (Gh) solar irradiances are measured and the relationship between the two radiant fluxes is investigated at Athalassa, Cyprus (35°15′N, 33°40′E, 165 m above MSL). These data are used to determine the temporal variability of the percentage ratio of solar global UV to solar global irradiation (Guv/Gh) and its dependence on various atmospheric conditions. Analyzing the data set, an inverse correlation between ozone column amount and the precise UV/Global ratio was found, which can be rather attributed to the change of various atmospheric parameters than the ozone column. The analysis of hourly percentage ratio values reveals a definite daily pattern with lower values during sunrise/sunset and higher values around noon. The variation of the percentage ratios (Guv/Gh) ranges from 3.95±0.29% in September to 2.92±0.42% in August for hourly values, while for daily values, the variation is between 2.85±0.32% in August and 3.68±0.1% in September, with annual mean values of 3.33±0.21% for hourly and 3.19±0.17% for daily data. Finally, the present data reveals a seasonal contribution of the aerosol extinction on the precise (Guv/Gh) ratio values. © 2005 Elsevier Ltd. All rights reserved