Abstract
Abstract Studying solar radiation is essential for human knowledge, since it is present in practically all its activities. Thus, the aim of this work was to analyze the climatic and seasonal variation of direct normal and global solar radiation in the region of Maceió, Alagoas State, Northeastern Brazil with sky conditions characterized by clearness index (Kt). The Kt was determined by the ratio between global solar irradiance and solar irradiance at the top of the atmosphere. The highest occurrences of daily direct normal solar irradiance under conditions of Kt ≥ 0.6 were recorded between 400 W m−2 and 700 W m−2 for all seasons. Under conditions of 0.4 ≤ Kt < 0.6, the daily direct normal solar irradiance occurred between 200 W m−2 and 500 W m−2 and for conditions of Kt < 0.4, its maximum value was 200 W m−2. It was observed that the levels of solar incidence in the study region depend on cloud cover conditions, with little influence of seasonality.
Highlights
IntroductionThe radiation emitted by the Sun that arrives at Earth (top of the atmosphere and terrestrial surface) is the main source of energy that influences practically all human activities (Liou, 2002; Muneer, 2004; Santos et al, 2014)
The radiation emitted by the Sun that arrives at Earth is the main source of energy that influences practically all human
Alagoas is subdivided into three geographic mesoregions (Coastal/Humid Zones, Hinterland and Interior) with different types of climate and further details are described in Santos et al (2014), Santos et al (2016) and Barros et al (2012)
Summary
The radiation emitted by the Sun that arrives at Earth (top of the atmosphere and terrestrial surface) is the main source of energy that influences practically all human activities (Liou, 2002; Muneer, 2004; Santos et al, 2014). Solar radiation studies require reliable and readily available data series for applications at the site of interest. The instrumentation to obtain IG and ID time series is given by the installation of a network of solar monitoring stations with radiometers and data acquisition system. The amount and spectral distribution of IG and ID depend on astronomical, atmospheric and local parameters such as: solar zenith angle, aerosol concentration and properties, amount of ozone, clouds, altitude of the site and surface albedo (Kaskaoutis and Kambezidis, 2009). ID is very sensitive to the optical depth of the aerosol and exhibits high frequency variation to the dynamic effects of clouds, showing greater spatial and temporal variability than IG, making it difficult to characterize daily and seasonal variability of solar radiation and its components (Kotti et al, 2014)
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