© 2015, IRJET ISO 9001:2008 Certified Journal Page 17 Evaluation of the correlation between Ultraviolet and Broadband Solar Radiation at a subtropical location (Qena, Upper Egypt) M. El-Nouby Adam 1,2 and Emad A. Ahmed 2 1 Quality Assurance Unit (ALI), King Saud University, Riyadh 11491, Saudi Arabia 2 Faculty of Science (Physics Department), South Valley University, Qena 83523, Egypt ---------------------------------------------------------------------***--------------------------------------------------------------------- Abstract - Although the study of ultraviolet solar radiation (UV) is important component of the environment, the concerned studies of this component are limited at Qena, Egypt (26.20, 32.70, 96 m asl). Thus, the hourly ratio of UV/G was estimated. The monthly average variation of these hourly values was discussed with respect to the change of some atmospheric parameters (ozone, water vapor and cloud). Through the whole period of this study, the average value of this ratio was compared with the same ratios of the other sites (inside and outside Egypt). In addition, a simple significant correlation between hourly values of UV and G has been established. Datasets for a new time period from Qena were used to validate the proposed equation. The study showed that, the estimated values of UV from this equation were in a good agreement with the corresponding measured values of UV (correlation coefficients was 0.94). These results were satisfactory to use these recommended correlation equation to estimate UV values that are difficult to measure or where measurements are available only for limited periods at any site in the zone of Upper Egypt. Furthermore, the study discusses the statistical results (correlation coefficients, modeling indexes, coefficients of modeling efficiency, root mean square errors, mean base errors and mean absolute errors) for the recommended correlation equation. Key Words: Ultraviolet solar radiation, Global solar radiation, Atmospheric parameters, Empirical model 1. INTRODUCTION The solar spectrum is a mixture of radiation: visible, ultraviolet and infrared radiation. The extra-terrestrial solar spectrum has a UV component that accounts for 9.3% of total solar radiation [1]. The complete UV waveband covers the wavelength range 100-400 nm [2]. Regarding its biological effects, UV radiation can be divided into three bands: UVA Dz͵ͳͷ-ͶͲͲ nmdz, UVB Dzʹ8Ͳ- ͵ͳͷ nmdz and UV-C DzͳͲͲ-ʹ8Ͳ nmdz. The effects of UV radiation on humans, the ecosystem, animals, plants, and materials are extensively studied and reported by several authors (e.g., [3-8]). The strength of solar beam undergoes complicated attenuation as it passes through the earth's atmosphere, where it is partially absorbed and partially scattered. The transmitted solar radiation reaches the earth's surface is then dependent on the following factors: (i) Scattering by air molecules (Rayleigh scattering) and aerosols, which is continuous function of wavelength without selective bands. (ii) Selective absorption by atmospheric gases (such as O3, H2O, CO2 and O2) at certain wavelengths. The aerosols also absorb radiation somewhat continuously in wavelengths, but much smaller than scattering by it [9]. Ozone absorbs mainly in the ultraviolet zone at wavelength less than 290 nm [10]. Water vapor absorption bands lay at the wavelength more than 700 nm. With the exception of ozone and water vapor, the main gaseous absorbers are Co2 and O2. Cloudiness plays an important role in atmospheric radiation transfer [11, 12]. In additions to cloud cover, the type and height of clouds can strongly affect the transmission of solar radiation through the lower atmosphere. Day-to-day changes of UV over the northern midlatitudes are dominated by the cloud variability [13]. The effect of clouds on UV levels can vary from small enhancements to almost total reduction. Under conditions with partial cloud cover, UV radiation also depends on the cloud positions relative to the Sun and the instrument. Consequently, the UV reaching the earthǯs surface has been modified by the atmosphere through which the radiation must pass. This modification is a function of the radiation path length through the atmosphere and the amount of each attenuator along that path length. The path length is determined by solar zenith angle, which is itself a function of latitude and time (of day and year). The current study was quantified the relationship between UV and G to estimate hourly total UV in all sky conditions. This is due to the fundamental role played by ultraviolet and due to the lack of long-term measurements of its magnitude. To satisfy this aim, Escobedo et al. (2011) [14] mentioned that one practical way to estimate UV is using empirical expressions derived from the correlation between G and its spectral component. The major International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 -0056 Volume: 02 Issue: 09 | Dec-2015 www.irjet.net p-ISSN: 2395-0072