Statistical Analysis and InterComparison of Albedo for Athalassa and Larnaca, Cyprus (original) (raw)
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SM journal of biometrics and biostatistics, 2017
A statistical analysis and inter-comparison of the Ultraviolet Radiation (UVR) at two sites in Cyprus representing two different climate regimes of the island (Athalassa-inland plain vs Larnaca-coastal location) covering the period 2013-2015 is presented. Mean annual and mean monthly daily totals of the UV irradiation and their frequency distribution at both sites are computed and discussed. The total accumulated UV irradiation along an average year reaches 398 MJ m-2 at Athalassa and 494 MJ m-2 at Larnaca. During summer, the daily UV radiation exceeds the value of 1800 kJ m-2 at Athalassa and 2200 kJ m-2 at Larnaca. Linear relationships were established between UVR and global solar radiation, with the coefficient of determination close to 1. These relationships indicate that UV irradiation corresponds to 5.9% and 6.8% of the horizontal global solar irradiation at the two sites, respectively. Four models were tested for the estimation of UVR and the best performed models were recalibrated according to the local conditions. Relationships between the clearness index (t k) and the UV hemispherical transmittance (tUV k) were also established. The annual tUV k is about 71% of t k. Finally, the dependence of the UV/G ratio values to the solar elevation angle and clearness index was also examined. It can be concluded that the presence of clouds reduces less the UV component rather than the global solar radiation, due to the strong absorption of water in the near infrared spectrum.
SM Journal of Biometrics & Biostatistics, 2017
A statistical analysis and inter-comparison of the broadband ultraviolet-B (UVB) radiation at two sites in Cyprus representing two different climate regimes of the island (Athalassa-inland plain vs Larnaca-coastal location) covering the period January 2013-December 2015 is presented. Mean annual and mean monthly daily totals of the UVB irradiation and their frequency distribution at both sites are computed and discussed. Daily maximum of hourly average irradiance values occur in July, 2.09 W m-2 , and minimum, 0.47 W m-2 , in December at solar noon at Athalassa. The respective values at Larnaca are slightly higher (2.48 W m-2 and 0.67 W m-2 , respectively). UVB daily values follow the pattern of the solar altitude angle; the total accumulated UVB irradiation along a mean year reaches 10.27 MJ m-2 at Athalassa and 13.49 MJ m-2 ; maximum stability of UVB takes place at midday hours during the summer. Large fluctuations of the daily UVB irradiation are observed in the spring months and November, which are mainly due to unstable meteorological conditions during the transition from cold to warm weather and vice versa. During summer the daily UVB radiation exceeds the value of 70 kJ m-2 at Larnaca and 55 kJ m-2 at Athalassa, while during the winter season the lowest is about 5 kJ m-2 at both stations. The UVB potential and extraterrestrial irradiation has also been calculated in order to estimate the attenuation of UVB radiation through the atmosphere. During summer the UVB transmittance is higher than in winter with a maximum value of 9% in July and a minimum of about 4% in December. Statistical relationships between UVB and other radiation components (UVA and global radiation) were established.
Applied Sciences
Athalassa is the main actinometric station of Cyprus and is located in the center of the island at a height of about 160 m. The station is equipped with shortwave and longwave radiation instruments. The time step of the measurements is 10 min, and hourly and daily values were derived for the period of June 2020–May 2021. The solar data underwent an extensive quality control process based mainly on the suggested tests of Baseline Surface Radiation Network (BSRN) for both the hourly and daily datasets. More than 98% of the data were within the limits recommended by the BSRN and other radiation networks. A statistical analysis of the shortwave solar radiation components was then performed. Linear and quadratic relationships were established between various radiation components, and their diurnal and monthly variability was assessed. The annual average daily global radiation amount was approximately 19 MJ/m2, whereas the amounts of horizontal beam and diffuse radiation were 12.9 MJ/m2 a...
Statistical analysis and inter-comparison of the global solar radiation at two sites in Cyprus
Renewable Energy, 2017
A statistical analysis and inter-comparison of the solar global radiation at two sites in Cyprus representing two different climate regimes of the island (Athalassa-inland plain vs Larnaca-coastal location) covering the period November 2012eJuly 2014 is presented. Mean annual, monthly and daily totals, the diurnal variation, frequency distribution of daily totals at both sites are computed and discussed. The validity of the Liu and Jordan approach to estimate mean hourly global radiation values is confirmed. The same type of statistical analysis was extended to the clearness index and sunshine duration. The results of this analysis are used to characterise and compare the radiation regimes at the two sites. The two sites are characterised by relatively high global and horizontal beam radiation intensities. The annual average daily global radiation intensities exceed the value of 18.5 MJ m À2 at the two sites, whereas the horizontal beam radiation is 11.5 MJ m À2 for Athalassa and 11.9 MJ m À2 for Larnaca, respectively. Consequently, the fraction of the beam component of the global radiation is relatively high at both sites, viz., the annual average daily fraction is > 0.600 at the two sites. Comparing the two sites it seems that Larnaca has slightly higher rates of global radiation than Athalassa, since the average yearly cumulative global irradiation is 6835 MJ m À2 for Athalassa and 7183 MJ m À2 for Larnaca. The annual coefficients of Angstrom formula were estimated using daily clearness index and relative sunshine data. The coefficient values for both stations were close to each other.
Applied Sciences, 2021
In this study, two years of hourly longwave downward and upward irradiance measurements at Athalassa, an inland location, are used to analyze and compare them. A detailed quality control process was followed according to the suggested tests proposed by the Baseline Surface Radiation Network (BSRN) group. The criteria involved are based on physically possible, extremely rare and climatological limits. Furthermore, comparison tests were also applied between the two longwave components as well as with air and ground surface temperatures. Additionally, time consistency and persistency tests were applied. All the suspect data were excluded from the analysis. The data showed that the frequency distribution of downward longwave irradiances follows a normal distribution function, while the upward longwave follows an almost normal distribution but with a long positive tail. The annual mean daily downward longwave irradiation is 27.3 MJ m−2 and the annual mean daily upward longwave irradiatio...
On the diffuse fraction of daily and monthly global radiation for the island of Cyprus
Solar Energy, 1996
Six years of hourly global and diffuse irradiation measurements on a horizontal surface performed at Athalassa, Cyprus, are used to establish a relationship between the daily diffuse fraction and the daily clearness index. Two types of correlations-yearly and seasonal-have been developed. These correlations, of first and third order in the clearness index are compared to the various correlations established by Collares-Pereira
Estimation of the ground albedo for the Athens area, Greece
Ground albedo can severely influence the estimation of solar radiation incident on tilted surfaces. Depending on the model used to calculate the reflected radiation, a significant error in the estimation of total radiation on an inclined surface is likely to be introduced. In the present work, several models for calculating the ground albedo are evaluated; the derived values are further used for estimating the ground-reflected radiation on a tilted surface. Four of these models are taken from the international literature and four new correlations are developed for the purpose of this study. All eight models are evaluated against measurements of ground-reflected radiation performed at the National Observatory of Athens in the period 1999-2008. The evaluation shows that the existing models, including that with a constant albedo value (0.2), perform relatively well. Nevertheless, if more accuracy is needed for scientific applications, site-specific models must be developed. Due to this demand new albedo models are derived for the Athens area that can perform efficiently all year round.
Journal of Geophysical Research, 2003
1] This paper compares seasonal and spatial variations of Moderate Resolution Imaging Spectroradiometer (MODIS) albedos with those from the Common Land Model (CLM) by land cover type. MODIS albedo data in the year 2001 were used to determine seasonal, spatial, and land cover dependence at 1 km resolution and to investigate the biases in CLM. Albedo dependence on vegetation type is smaller than that on snow and soil. Snow causes the largest temporal and spatial variations, especially in the visible band (0.3-0.7 mm). CLM has visible albedos that are lower by up to 0.4-0.5 in winter over northern high latitudes but are globally higher by 0.02-0.04 in summer over most vegetation, mainly due to its overestimated leaf and stem area index in winter and slightly higher prescribed canopy albedos in summer, respectively. MODIS and CLM differ considerably in soil albedo over desert and semidesert regions, especially in the near-infrared band (0.7-5.0 mm), with the largest low bias of about 0.1 in the Sahara. Adjustments of the prescribed albedos in CLM based on MODIS observations could reduce such biases. Therefore the model should better represent leaf and stem area index, vegetation albedo in the presence of snow, and soil albedo. Citation: Zhou, L., et al., Comparison of seasonal and spatial variations of albedos from Moderate-Resolution Imaging Spectroradiometer (MODIS) and Common Land Model,
The Land Surface Albedo (LSA) was estimated in the broader Mediterranean area, on an 8-day basis, for the period 2001–2012. MODIS (Moderate Resolution Imaging Spectroradiometer) albedo product parameters, at 1 km x 1 km spatial resolution, were used. LSA changes during the above study period were also estimated, based on annual average values. Results revealed increasing LSA trends dominating in the Levant region and decreasing inNW Africa, of the order of 3.3% and 6.6%, respectively, while mixed signs were observed in southern Europe. Three factors that can determine the LSA changes were investigated: land cover changes, rainfall changes and Aerosol Optical Thickness (AOT) spatio-temporal variability. The analysis made clear that land cover and rainfall changes affect LSA at local and regional scales, while the effect of AOT was not important. Land cover changes revealed deforestation hot spots, where LSA was increased by 13%–14%, while an increase in rainfall over many areas in NW Africa appears to have caused a corresponding decrease in LSA by over 5%. These findings highlight the importance of a global and continuous LSA monitoring at both regional and local scales, which is necessary for both climate monitoring and modeling studies.
Editorial for Special Issue: “Remotely Sensed Albedo”
Remote Sensing
Land surface (bare soil, vegetation, and snow) albedo is an essential climate variable that affects the Earth’s radiation budget, and therefore, is of vital interest for a broad number of applications: Thematic (urban, cryosphere, land cover, and bare soil), climate (Long Term Data Record), processing technics (gap filling, data merging), and products validation (cal/val) [...]