# Geographical Distribution of Global Radiation and Sunshine Duration over the Island of Cyprus
## 1 Introduction  
Solar radiation is the main source of energy that affects the atmospheric environment [1], climate [2] and ecosystems [3]. The knowledge of the local solar radiation profile is important for the design solar energy systems. Information on solar energy is used in many applications that seek to optimize the capture of solar energy, so that it is possible to reach energy savings and carry out sustainable energy consumption [4, 5, 6]. Furthermore, solar radiation data are essential for applications in meteorology, agriculture, crop modeling as well as in the health sector [3, 7]. Two elements of solar radiation components are the most popular elements registered by weather stations: (i) global irradiance data measured on a horizontal surface and (ii) sunshine duration (SD). The SD is recorded as long the direct normal solar irradiance exceeds the value of 120 W/m\({}^{2}\). However, the sunshine duration is a parameter of secondary significance in the determination of the climatologyat a site, while the prime parameters are temperature, humidity, wind, precipitation, and solar radiation [8; 9; 10; 11]. Nevertheless, sunshine duration is important in estimating solar radiation [11]. Additionally, solar radiation fractions, such as the direct and diffuse fractions to global radiation, are required for several applications. For example, the direct component is a basic input to predict the performances and to design concentrating solar plants [8]. Different models can be found in the literature to estimate these two components. The solar radiation intensity is affected by the presence of the atmospheric constituents [12; 13; 14], the variations in the amount and texture of clouds as well as by the Sun-Earth geometry [1]. Therefore, clouds and aerosols are the main factors that play a significant role in determining the solar radiation climate at a site. These factors vary over space and time, causing an analogous variability in solar radiation. The estimation of global irradiance and the prediction of its components, i.e., direct, diffuse and reflected radiation, has been widely discussed in the literature. Since the pioneer contribution by [PERSON] and [PERSON] [15], several models and comparative analyses have been presented and discussed. An extensive review of the measurements and modeling of all shortwave radiation components has been given by [PERSON] [11] and more recently by [PERSON] [16]. Generally, two categories of solar radiation models can be distinguished. In the first category belong models that are based on meteorological data, such as cloudiness, sunshine duration, and turbidity of the atmosphere [17; 18; 19; 20; 21]. Details about the computation procedure of the said models are given by [PERSON] [22]. In the second category belong models that use the decomposition method where the global irradiance is split into its direct and diffuse components and are basically based on clearness index and diffuse or direct fractions. In this category, we could classify the models of [PERSON] [23], [PERSON] et al. [24], [PERSON] et al. [25], and [PERSON] et al. [26] could be classified, to mention just some of them. The separation models are still highly popular [27]. They are often described as site-dependent in the literature because they are essentially empirical in nature. The Boland model was found to perform satisfactorily at different sites of the world. Furthermore, in order to cover wide areas on Earth, satellite observations are supplied [28; 29]. The solar radiation climate provides the levels, trends, and frequencies of global radiation and its components. Indicative studies for different parts of the world have been published in the literature. For example, [PERSON] et al. [30] presented the solar climate of Africa, while [PERSON] [5] reported the solar climate of Athens. More recently, [PERSON] [2] presented the solar climate and the sky-status climatology of Greece [31].