•Statistical analysis of global radiation.•Monthly and diurnal variation of global radiation.•Frequency distribution of global radiation.•Relationship between global and other radiation ...parameters.•Comparison of global radiation between two sites.
A statistical analysis and inter-comparison of the solar 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 global, horizontal beam and diffuse radiation and their frequency distribution at both sites are computed and discussed. The values of skewness and kurtosis coefficients are used to define the frequency distribution type of the above radiation parameters on a monthly basis. The statistical analysis is extended to the daily clearness index (KT), diffuse ratio (KD), and the ratio of horizontal beam to global radiation (KB,G). Furthermore, the influencing factors on the magnitude of the radiation components were examined. The value of KT was used to classify three different types of days such as clear, partially cloudy and cloudy days. Then, a statistical analysis of the solar radiation components was performed. On an average annual basis, more than 80% of the days are classified as either clear or partially cloudy at both stations. Additionally, the influence of the atmospheric absorption and scattering of the solar radiation under clear skies was examined on the basis of the Linke turbidity factor (TL). The results of this analysis are used to characterize and compare the radiation regimes of the two sites. Both sites have relatively high intensity of global and direct horizontal radiation. The annual average daily global radiation intensity is 18.5MJm−2 at Athalassa and 19.9MJm−2 at Larnaca. The horizontal beam radiation is 13.1MJm−2 for Athalassa and 14.2MJm−2 for Larnaca. Therefore, the fraction of the beam component of the global radiation is comparatively high at both sites, as indicated by the annual average daily fraction which is greater than 0.600. Generally, Larnaca has slightly higher rates of global radiation than Athalassa, as indicated by the average yearly cumulative global irradiation which is 6763MJm−2 for Athalassa and 7274MJm−2 for Larnaca.
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.
•Procedures used to test the quality of shortwave and longwave radiation measurements.•The quality process for the 10 min average irradiances, hourly irradiation and the respective daily values.•This paper reviews presently available procedures for quality assessment of the solar irradiation data.•The final step of the quality control procedure refers to the analysis of daily and annual variations of radiation parameters.
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 2012–July 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−2 at the two sites, whereas the horizontal beam radiation is 11.5 MJ m−2 for Athalassa and 11.9 MJ m−2 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−2 for Athalassa and 7183 MJ m−2 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.
•Statistical analysis of global radiation.•Monthly and diurnal variation of global radiation.•Frequency distribution of global radiation.•Relationship between global and other radiation parameters.•Comparison of global radiation between two sites.
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 of ultraviolet erythemal radiation.•Monthly and diurnal variation of ultraviolet erythemal radiation.•Statistical relationships between ultraviolet erythemal and other radiation components.•Calculation of UV Index.•Estimation of the cumulative doses during an average year for the four skin phototypes.
Floods are one of the most common natural disasters worldwide, leading to economic losses and loss of human lives. This paper highlights the hydrological effects of multi-temporal land use changes in ...flood hazard within the Yialias catchment area, located in central Cyprus. A calibrated hydrological model was firstly developed to describe the hydrological processes and internal basin dynamics of the three major subbasins, in order to study the diachronic effects of land use changes. For the implementation of the hydrological model, land use, soil and hydrometeorological data were incorporated. The climatic and stream flow data were derived from rain and flow gauge stations located in the wider area of the watershed basin. In addition, the land use and soil data were extracted after the application of object-oriented nearest neighbor algorithms of ASTER satellite images. Subsequently, the cellular automata (CA)-Markov chain analysis was implemented to predict the 2020 land use/land cover (LULC) map and incorporate it to the hydrological impact assessment. The results denoted the increase of runoff in the catchment area due to the recorded extensive urban sprawl phenomenon of the last decade.
In this work, hourly measurements of global solar irradiances obtained from a pyranometer and direct normal irradiances obtained from sunshine duration sensor are assessed through an extensive ...quality control procedure and statistical analysis on the measured and derived solar parameters for a semimountainous location using data from the last fie years (2016-2020). This information and the method suggested concerning the solar energy capture systems and energy efficiency is useful for engineers who can therefore take knowledge of the local radiation levels. Furthermore, the direct horizontal irradiance canbe easily calculated and the diffuse component can be estimated from the difference of global and direct horizontal irradiances. Monthly mean hourly values of the radiation components are also estimated and shown through isolines diagrams. Representative values of global direct and diffuse irradiances for different times of the year and different hour of the day can be easily read from these diagrams. Simultaneously, a similar analysis is carried out over various solar indices estimated on both an hourly and daily basis. The derived solar indices are the clearness index for global, direct, and diffuse radiation as well as the diffuse and direct fractions from global radiation. The interrelationships between the said indices are also examined.Additionally, the BRL (Boland-Ridley-Lauret) diffuse fraction model which is a multiple predictor logistic model was tested and can be used to estimate the diffuse and later the direct radiation component. The model is a function of clearness index (kt), the apparent solar time (AST), the solar altitude (αs), the daily clearness index (KT) and persistence parameter ψ which is an average of both a lag and lead of the clearness index. The outcome of the model shows that it can be used to estimate successfully the diffuse radiation.
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.
•Quality control processes of longwave radiation components.•Statistical analysis of downward and upward longwave radiation.•Statistical relationships of hourly and daily longwave radiation values.•Modelling longwave radiation components under clear-sky and all-sky conditions.•Comparison of the longwave radiation between two sites.
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 and Rabl (1979), Newland (1989), Erbs
et al. (1982), Rao
et al. (1984), Page (1961), Liu and Jordan (1960) and Lalas
et al. (1987). The comparison has been performed in terms of the widely used statistical indicators (MBE) and (RMSE) errors: an additional statistical indicator, the
t-statistic, combining the earlier indicators, is introduced. The results indicate that the proposed yearly correlation matches the earlier correlations quite closely and all correlations examined yield results that are statistically significant. For large
K
T
> 0.60
values, most of the earlier correlations exhibit a slight tendency to systematically overstimate the diffuse fraction. This marginal disagreement between the earlier correlations and the proposed model is probably significantly affected by the clear sky conditions that prevail over Cyprus for most of the time as well as atmospheric humidity content. It is clear that the standard correlations examined in this analysis appear to be location-independent models for diffuse irradiation predictions, at least for the Cyprus case.
Robust and accurate estimates of rainfall frequencies are difficult to make with short, and arid-climate, rainfall records, however new regional and global methods were used to supplement such a ...constrained 15–34 yr record in Cyprus. The impact of supplementing rainfall frequency analysis with the regional and global approaches was measured with relative bias and root mean square error (RMSE) values. Analysis considered 42 stations with 8 time intervals (5–360
min) in four regions delineated by proximity to sea and elevation. Regional statistical algorithms found the sites passed discordancy tests of coefficient of variation, skewness and kurtosis, while heterogeneity tests revealed the regions were homogeneous to mildly heterogeneous. Rainfall depths were simulated in the regional analysis method 500 times, and then goodness of fit tests identified the best candidate distribution as the general extreme value (GEV) Type II. In the regional analysis, the method of L-moments was used to estimate location, shape, and scale parameters. In the global based analysis, the distribution was a priori prescribed as GEV Type II, a shape parameter was a priori set to 0.15, and a time interval term was constructed to use one set of parameters for all time intervals. Relative RMSE values were approximately equal at 10% for the regional and global method when regions were compared, but when time intervals were compared the global method RMSE had a parabolic-shaped time interval trend. Relative bias values were also approximately equal for both methods when regions were compared, but again a parabolic-shaped time interval trend was found for the global method. The global method relative RMSE and bias trended with time interval, which may be caused by fitting a single scale value for all time intervals.
Long term temperature data from two stations on the island of Cyprus have been analysed. Increasing trends of approximately 1°C/100 years in the annual mean temperatures are found at both stations. ...However, the minimum daily temperatures have generally increased at a larger rate than the maximum daily temperatures, resulting in a decrease in the long-term diurnal temperature range. This decrease ranges from −0.5°C/100 years to −3.5°C/100 years, depending on the location. The reduction in the diurnal temperature range is consistent with observations from other parts of the globe, and may indicate that the climate in this region of the globe is part of a larger global climate change that has been occurring over the last century. It is possible that long term changes in greenhouse gas concentrations in the atmosphere are responsible for the long-term annual mean temperature increase. Furthermore, the changes in the diurnal temperature range can possibly be explained by increases in cloud cover and/or tropospheric aerosols. It is possible that part of these changes is caused by local land-use changes, primarily by the increasing urbanization of Cyprus.
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