Neural Networks Estimations of Downward Longwave Radiation in Nigeria Environmet

ABSTRACT

The earth‟s surface is affected by three main types of radiation from the sun: global solar (or total), beam (or direct), and longwave (or indirect) radiation. Global solar radiation is composed of direct and indirect radiation. Approximately 99% of the total radiation from the sun that reaches the earth is beam radiation, which has a wavelength range of 0.29 to 3.9 μm and is not subjected to interference from any interspatial matter. The remaining 1% is longwave radiation, which falls into the range of 4 to approximately 50 μm and encounters interference with matter on its way from the sun. Furthermore, downward longwave radiation (DLR) can be classified into three types: before, between, and after the DLR range of approximately 8 to 12 μm. The wavelength region between 8 to 12 μm is known as the atmospheric window that DLR comes directly from space. Additionally, there is net longwave radiation at the surface of the earth, which is caused by the difference between the downward and upward longwave radiations. Gases that absorb and radiate DLR include water molecule (H2O), carbon dioxide (CO2), ozone (O3), nitrous oxide (N2O), carbon monoxide (CO), oxygen (O2), methane (CH4), and nitrogen (N2). The nature of the interaction between DLR and these gases and aerosols is dependent on the type of atmosphere, and the major absorbers of DLR are water molecules (Coulson, 1975; Niemela et al., 2001; Liang et al., 2012; Cotton et al., 2010).

Although the beam radiation can only be received during a certain period of the daytime, and by extension, global radiation also has this limitation, downward longwave radiation is received 24 hours a day. By virtue of the diurnal disposition of DLR, DLR is an important parameter of both radiant and energy aspects of the atmosphere. Because DLR is primarily in