# Solar Ultraviolet Irradiance Characterization under All Sky Conditions in Burgos, Spain
## 3 Results and Discussion
### Hourly, Monthly, and Seasonal Analysis of the GHUV/GHI Ratio  
Figure 6 shows the boxplot of the mean hourly values of the _GHUV/GHI_ ratio, calculated from the average of the 10 min data, from sunrise to sunset, using the whole database. The graph represents the mean value (gray crosses), the median (white lines), the three quartiles, and both the maximum and minimum data values, as well as the outlier values. The mean hourly value of _GHUV/GHI_ remained almost constant throughout the day. As previously noted, a small increase can be seen in the early hours of the day, which tends to stabilize during the central hours, and increases again at sunset. As the interquartile range shows, a greater dispersion of values in the first and last hours (1.9% at 5:00 h and 19:00 h), than in the central hours (0.75% at 12:00 h), of the day is observable. The average values were higher than the median values across all hours of the day. The hourly average of the ratio was 3.98 \(\pm\) 0.82%, with maximum and minimum values of 4.25 \(\pm\) 1.49% and 3.80 \(\pm\) 1.14%, at 19:00 and at 18:00 h, respectively. These data, shown in Table 1, are comparable with other data from different locations in Spain. The hourly _GHUV/GHI_ ratio in Burgos is higher than the ratio recorded at Almeria (3.7%) [53], and lower than the ratios recorded at Granada (4%) [53], Valladoidi (4.1%) [22], Valencia (4.2%), and Cordoba (4.9%) [23]; this is mainly due to each location's different sky conditions and their various heights above sea level.  
Figures 7 and 8 show the statistical analysis of the monthly and seasonal averages of the _GHUV/GHI_ ratio, which was calculated using the averages of the 10 min dataset, using the whole database. Figure 7 shows that the monthly data were almost constant throughout the year, with a small decrease in July and August. The standard deviation fluctuated between 0.69 and 1.23%, and the interquartile range was between 0.44% and 1.56%. December and January were the measurement campaign months with the highest data dispersion: the interquartile ranges were 1.51% and 1.56% with standard deviations of 1.29% and 1.27%, respectively. The maximum value was recorded in December (4.35% \(\pm\) 1.29%), whereas the minimum was reached in July (3.82% \(\pm\) 0.69%). A greater dispersion of values is observable in Figure 8 for the winter and autumn months, whereas the values in the summer months were closer, and therefore, they presented a smaller dispersion. These results are similar to the results obtained at other locations around the world (see Table 1), and the main differences between them can be attributed to the specific sky conditions, rather than the temporal variability of the ratio.  
Figure 5: Cumulative distribution function (**a**) and probability distribution function (**b**) of the 10 min data measured during the experimental campaign. Both the empirical CDF and PDF (blue line), and the CDF and PDF that were adjusted to a normal distribution function (yellow line), are plotted.  
Figure 8: Boxplot of the _GHIU/GHI_ seasonal averages based on the 10 min datasets.  
Figure 6: Boxplot of the _GHIU/GHI_ hourly averages using the 10 min data. Gray crosses indicate the mean, and the white lines inside the box indicate the median. The limits of the boxes define the first, second, and third quartiles, whereas the extreme whiskers show the minimum and the maximum points. Black and gray circles represent outliers.  
Figure 7: Boxplot of the _GHIU/GHI_ monthly averages based on 10 min datasets.