Quality control of solar shortwave and terrestrial longwave radiation for surface radiation measurements at two sites in Cyprus

Routine measurements of irradiance are valuable for many research fields such as energy applications. However, ground data of solar global radiation can present questionable values. In this study, a set of check procedures is used to test the quality of shortwave and longwave radiation measurements taken at two actinometric stations in Cyprus (Athalassa-inland location and Larnaca-coastal location), during the period November 2012-July 2014. The testing procedures include physically possible limits for all the radiation components and comparisons between global radiation and the sum of direct and diffuse radiation. The quality process is implemented to both the 10-min averaged irradiances, hourly irradiation and the respective daily values. This paper reviews the currently available procedures for quality assessment of the solar shortwave and longwave irradiation data. In the present study, the first level of test includes physical possible limits which are determined by the Daylight Research Group and the Baseline Surface Radiation Network of the World Meteorological Organisation (WMO). The second level of test is a semi-automated procedure that is based on the creation of an envelope in the clearness index and the diffuse to global irradiance ratio. The third level of test is based on the comparison of various radiation parameters including comparison of measured extreme values with theoretical estimations from clear sky-models. The fourth level of test of the quality control procedure refers to the analysis of daily and annual variations of the radiation parameters

Characteristics of downward and upward longwave radiation at athalassa, an inland location of the island of Cyprus

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 frequency distribution of downward longwave irradiances, the data showed that it 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 irradiation is 37.8 MJ m−2. The net longwave irradiation is always negative ranging from −5.9 to −12.1 MJ/m2. Various models were tested to estimate daylight and all day downward and upward longwave irradiances under clear-sky and all-sky conditions. For the comparison of measured and estimated values the root-mean-square errors and linear regression correlations have been used. The results of this comparison showed that Idso’s and Brunt’s models perform well, and they can be used to estimate downward longwave irradiance under clear-sky conditions. Furthermore, both models were extended to estimate the daylight downward longwave irradiance under all-sky conditions by taking into account the ratio of global to the clear-sky global solar irradiance. In this case, the RMSE of the local calibrated coefficients scheme of Idso’s model was 30.6 W m−2, while Brunt’s model showed slightly lower value (29.0 W m−2)

Statistical analysis and inter-comparison of erythemal solar radiation for Athalassa and Larnaca, Cyprus

A statistical analysis and inter-comparison of the erythemal ultraviolet radiation (UVER) 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 UVER irradiation and their frequency distribution at both sites are computed and discussed. UVER irradiance fluctuates between 0.054 W m−2 in December to 0.227 W m−2 in July at solar noon at Athalassa. The values at Larnaca are lower than in Athalassa and they fluctuate between 0.043 W m−2 in December and 0.172 W m−2 in July at solar noon. The total accumulated UVER irradiation along a mean year reaches 1142 kJ m−2 at Athalassa and 909 kJ m−2 at Larnaca. Large fluctuations of the daily UVER 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 UVER radiation exceeds the value of 6 kJ m−2 at Athalassa and 4.8 kJ m−2 at Larnaca, while during the winter season the lowest is about 0.2 kJ m−2 at both sites. Statistical relationships between UVER and other radiation components (UVA, global radiation, clearness index and relative optical air mass) are established. The UV Index reaches high (6–7) or very high (8–10) values in 58.1% of the cases in Athalassa, whereas in Larnaca these values are reached in 38.8%. It is observed that the cumulative doses of UVER during an average year range from 9087 Standard Erythemal Dose (SEDs) in Larnaca to 11418 SEDs in Athalassa. The most common skin type in Cyprus, phototype III (about 70% of the population), could receive an annual cumulative dose between 2596 Minimum Erythemal Doses (MEDs) in Larnaca to 3262 MEDs in Athalassa

Statistical Analysis and Inter- Comparison of Solar UVA and Global Radiation for Athalassa and Larnaca, Cyprus

A statistical analysis and inter-comparison of the broadband ultraviolet-A (UVA) 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 UVA irradiation and their frequency distribution at both sites are computed and discussed. Daily maximum of hourly average irradiance values occur in July, 58W m-2 and minimum, 22 W m-2, in December at solar noon at Athalassa. The respective values at Larnaca are slightly higher (68 W m-2 and 28 W m-2, respectively). UVA daily values follow the pattern of the solar altitude angle; the total accumulated UVA irradiation along a mean year reaches 385.8 MJ m-2 at Athalassa and 476.5 MJ m-2; maximum stability of UVA takes place at midday hours and during the summer. Large fluctuations of the daily UVA irradiation are observed in the winter and spring months, which are mainly due to unstable meteorological conditions during the transition from cold to warm weather and vice versa. During summer the daily UVA radiation exceeds the value of 1700 kJ m-2 at Athalassa and 2100 kJ m-2 at Larnaca, while during the winter season the lowest is about 250 kJ m-2 at both stations. The UVA potential and extraterrestrial irradiation have also been calculated in order to estimate the attenuation of UVA radiation through the atmosphere. The UVA transmittance, kUVA, is approximately 6 to 7% of the hemispherical transmittance for the whole spectrum (kt). Statistical relationships between UVA and other radiation components were established using linear or power relationships

Geographical Distribution of Global Radiation and Sunshine Duration over the Island of Cyprus

In this work, hourly measurements of global solar irradiances obtained from pyranometers and sunshine duration data using either Kipp & Zonen CSD3 automatic sensors or Campbell–Stokes sunshine recorders were assessed through an extensive quality control procedure and statistical analysis on the measured and derived solar parameters for all the actinometric stations installed in various locations over the island of Cyprus, covering mainly the period 2019–2021. This information is useful for engineers concerning the solar energy capture systems and energy efficiency who can therefore take knowledge of the local radiation levels. Monthly mean hourly values of global radiation and sunshine duration are calculated and shown through isoline diagrams. During June or July, daily global irradiations ranged between 25 MJ/m2 and 30 MJ/m2, with the lowest occurring in the mountainous locations. On the other hand, in January or December, they ranged between 6.5 MJ/m2 and 10.5 MJ/m2. The total annual number of hours of sunshine duration ranged between 2500 and 3500, with the lowest values recorded at the mountainous sites. The clearness index and relative sunshine duration were used for the classification of the weather conditions over the island. Furthermore, the interrelationships between the said indices were used for the estimation of global radiation. This work has specifically contributed to the characterization and analysis of hourly and daily solar global radiation. Furthermore, the measurements on the ground level could be compared with satellite observations in order to improve the geographical distribution of global radiation, especially in areas where no measurements exist. The analysis could be also extended for the other shortwave radiation components (Direct, Diffuse and Photosynthetic Active Radiation (PAR)) in order to assess the solar radiation regime over the island

Characteristics of longwave radiation through the statistical analysis of downward and upward longwave radiation and inter-comparison of two sites in Cyprus

In this study, three years of hourly longwave downward and upward irradiance measurements for two sites in Cyprus representing two different climate regimes (inland vs coastal locations) are used to analyse and compare them. The quality control process was based on physically possible, extremely rare and climatological limits. Furthermore, comparison tests between the two longwave components as well as with air and ground surface temperatures were used to evaluate the hourly values of longwave irradiances. The annual mean daily downward longwave irradiation at Athalassa is 29.1 MJ m −2 and at Larnaca it is slightly higher (31.3 MJ m −2 ). On the other hand, the annual mean daily upward longwave irradiation at Athalassa is 38.2 MJ m −2 , while at Larnaca it is slightly lower (37.4 MJ m −2 ). The performance of various models in estimating the daylight downward and upward longwave irradiances under clear-sky and all-sky conditions was evaluated. Root-mean-square errors, mean bias errors, and linear regression correlations have been used to compare measured and estimated values. The results of this comparison for the station of Athalassa, showed that Idso's model perform well and it can be used to estimate downward longwave irradiance under clear-sky conditions. Furthermore, Idso's model was extended to estimate the daylight downward longwave irradiance under all-sky conditions by taking into account the ratio of global to the clear-sky global solar irradiance. The RMSE of the local calibrated coefficients scheme of Idso's model was 17.70 W m −2 . For the estimation of the daylight upward longwave irradiance under all-sky conditions, the calibrated Dognieux and Lemoine model was used which performed well. The RMSE in this case was 12.75 W m −2

Characteristics of Photosynthetic Active Radiation (PAR) Through Statistical Analysis at Larnaca, Cyprus

Measurements of Photosynthetically Active Radiation (PAR) and global solar radiation at Larnaca (a coastal site in Cyprus) during the period 3013-2015 were used to investigate the seasonal characteristics of PAR and PAR/G ratio (PAR fraction or fFEC). PAR showed seasonal features with higher values in summer and lower values in winter. The annual mean values of PPFD and fFEC being 40.3 mol m-2 d-1 and 2.03 mol M J-1, respectively. Monthly average daily PAR increased from 19.1 mol m-2 d-1 (in December) to 59.6 mol m-2 d-1 (in June).The monthly daily average of fFEC remained almost constant throughout the year at Larnaca. The spatial variability of PAR was also investigated using measurements from other four sites with different climate characteristics. The annual mean daily PAR value ranged between 31.7 to 40.0mol m-2 d-1. The highest values are recorded in the coastal stations (Larnaca and Paralimni). The annual average value of fFEC at the five observation sites ranged from 1.82 mol MJ-1 to 2.03 mol MJ-1, in accordance to what is observed in most parts of the world. The highest appeared in the coastal sites of Larnaca and Paralimni due to the presence of high water vapour atmospheric concentrations. Elevation plays a significant role on the values of the above variables. As a general trend, fFEC followed the order Clea