Sunshine, global radiation and net radiation in Brazil

Abstract

This paper characterizes the spatial and temporal distribution of the sunshine, global radiation and net radiation in Brazil as well as the regional potential in the country, regarding these climatic parameters. Monthly and annual maps of these parameters, based on measured and estimated data from 204 meteorological stations distributed throughout the Brazilian territory, and temporal-spatial diagrams, derived from south-north and west-east transects, show the trends in variation of these parameters and their relation to the various regional attributes of Brazil. These maps and diagrams contemplate both geographic aspects (vegetation, hydrography, orography, and geomorphology), and climatic elements (cloudiness and rain). Considering the absence of measured global radiation data, Angström’s equation of 1924 was used, which takes into account the sunshine data. An estimate of the radiation balance (net radiation) was obtained by Linacre’s equation of 1967. The maps of sunshine, global radiation and net radiation allowed the visualization of the spatial distribution of these elements. In the northern region, the sunshine is lower in areas with higher precipitation rates, such as around the Amazonas River mouth and in the Amapá State. Global radiation presents high values and little variation due to the high transmissivity of the atmosphere. Due to the uniformity of the relief and albedo, the net radiation also presents high values. In the northeast, high values of sunshine are explained by low cloudiness, especially in the semi-arid region (Caatinga / Sertão Nordestino). The maximum values of net radiation occur in the littoral. In the central-west region, in areas with greater amount of precipitation, the sunshine values are low. Global radiation and net radiation  present similar values to those for the northern region. In southeastern Brazil, the distribution of sunshine is conditioned by factors such as relief, cloudiness and precipitation. Global radiation and net radiation are distributed more irregularly due to cloud cover, as in the case of the Rio Doce Basin, where the values are quite low. Net radiation is influenced by the albedo, which varies according to land use. In the South, all the elements exhibit orographic effects, which produces gradients from the coast towards the interior. Based on the spatial distribution of sunshine, global radiation and net radiation, Brazil’s potential for solar energy can be verified as to qualitaty, quantity and consumptive use. This research also contributes to the agricultural planning regarding agroclimatic zoning, and crop forecasting; and to urban planning, in order to more adequately take into account the radiation balance concerning the ordering of vertical growth and the increase of green areas.