Diurnal Sensitivity of Surface Solar Radiation to Aerosol Loading: A DISORT-Based Radiative Transfer Study
Sibgatullah Mustapha Wali
Hussain Yusuf
Usman Idris Ismail
Yahaya Aliyu
Abdulrahim Muhammad Majia
Abstract
Aerosols modify surface solar radiation primarily through extinction processes involving scattering and absorption, with impacts that depend strongly on solar geometry and aerosol optical properties. Despite widespread use of radiative transfer models, limited attention has been given to isolating the sensitivity of diurnal surface irradiance to aerosol loading under controlled parameter assumptions in aerosol rich regions such as West Africa. In this study, the Discrete Ordinate Radiative Transfer (DISORT) method is used to quantify the diurnal response of clear sky surface solar irradiance to varying aerosol optical thickness (AOT). Simulations were conducted at 10 minutes intervals from sunrise to sunset for AOT values of 0.5, 0.85, and 1.2, representing low to high aerosol loading, while single scattering albedo and backscattering fraction were held constant to isolate first-order AOT effects. Results show that increasing AOT leads to systematic attenuation of surface irradiance throughout the day, with midday reductions of approximately 15–30% relative to moderate aerosol conditions and stronger relative losses during early morning and late afternoon due to enhanced optical air mass. The study highlights the angular dependence of aerosol radiative effects and demonstrates the usefulness of idealized DISORT simulations as a baseline framework for understanding diurnal solar energy availability under heavy aerosol loading. Model assumptions and uncertainties are discussed to clarify the scope and applicability of the results.
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