Estudo da radiação solar global e do índice de transmissividade (kt), externo e interno, em uma floresta de mangue em Alagoas - Brasil

Mangrove forests are of extreme social, economic and environmental importance, because they sustain a rich fauna and flora. Brazil possesses one of the largest mangrove areas in the world, which extends from the extreme north to the southern regions of the country, covering the entire coast. Due to such vast expanse, altering the state of the mangrove forests has a direct influence on the microclimate of the region. From the meteorological perspective, it is necessary to limit the exploitation of this ecosystem because the destruction of the mangrove forests exposes the surface area to direct solar radiation, thus changing the total net radiation. Therefore, one of the prime factors in understanding the availability of energy to the diverse processes of the system is knowing how the Solar Global Radiation (Rg) and its components, Diffuse Radiation (Rd) and Direct Radiation (RD), behave in the forest. The main objective of this research was to evaluate and compare the behavior of the Rg and it components, inside and above the mangrove forest. The solar radiation measurements are from a micrometeorological tower installed inside a mangrove forest, located at the Marechal Deodoro municipal district (15 km from Maceio, Alagoas) in an environmentally protected area (APA) called APA de Santa Rita. The tower was situated at 9° 42'18''S and 35°48'32"W coordinates, and operating from October 2004 to September 2005. The Rd data were collected with a CM5 Kipp and Zonnen pyranometer, which was equipped with a 10 cm width by 80 cm diameter shadow ring. A SP - LITE pyranometer from Campbell Scientific measured the Rg. The atmospheric transmissivity index Kt (Rg/Ro) where Ro is the top atmospheric radiation, was also obtained by an empiric method. The results showed great variation between the dry and rainy season relative to the maximum Rg value, due to the variation on the atmospheric transmissivity conditions. Inside the forest, it was observed that the penetration of the solar rays through the canopy is dependent upon the solar zenith angle (Z), and a reduction up to 66% was eobserved between the dry and rainy seasons. It was also verified that up to 35% of incidental radiation at the top of the canopy reached the internal surface below the mangrove forest, reducing to only 15% during rainy season.