Abstract
Default aerosol extinction coefficient profiles are commonly used instead of measured profiles in radiative transfer modeling, increasing the uncertainties in the simulations. The present study aimed to determine the magnitude of these uncertainties and contribute towards the understanding of the complex interactions between aerosols and solar radiation. Default, artificial and measured profiles of the aerosol extinction coefficient were used to simulate the profiles of different radiometric quantities in the atmosphere for different surface, atmospheric, and aerosol properties and for four spectral bands: ultraviolet-B, ultraviolet-A, visible, and near-infrared. Case studies were performed over different areas in Europe and North Africa. Analysis of the results showed that under cloudless skies, changing the altitude of an artificial aerosol layer has minor impact on the levels of shortwave radiation at the top and bottom of the atmosphere, even for high aerosol loads. Differences of up to 30% were, however, detected for individual spectral bands. Using measured instead of default profiles for the simulations led to more significant differences in the atmosphere, which became very large during dust episodes (10–60% for actinic flux at altitudes between 1 and 2 km, and up to 15 K/day for heating rates depending on the site and solar elevation).
Highlights
Solar radiation is the primary source of energy on Earth, affecting many physical, chemical and biological processes on the planet
Very limited information is available on how this simplification affects the simulated radiation (e.g., [20,23])
Climatology [56] and investigated how changes in the vertical distribution of aerosols affect the distribution of shortwave radiation in the atmosphere under cloudless skies
Summary
Solar radiation is the primary source of energy on Earth, affecting many physical, chemical and biological processes on the planet. The spectral distribution of the optical properties of aerosols, in conjunction with differences in the scattering and the absorption of radiation at different wavelengths by atmospheric molecules, further increases the uncertainty in the modeling of solar radiation [17–19]. Basin and North Africa, dust plays a key role in the attenuation of solar irradiance, and near the extra-tropics its role is comparable or more significant (over arid or semi-arid areas) relative to the role of clouds [31–34] Other aerosol species such as maritime aerosols strongly affect various atmospheric processes over the Mediterranean Basin (e.g., [35]), but their concentrations are high near the surface and degrade strongly with altitude (e.g., [36]). Photochemical processes depend on the amount of available solar radiation, either at particular wavelengths or across broader spectral bands [46–48] Such processes take place at different altitudes in the atmosphere, determine atmospheric composition, and play a key role in air quality [49–52]. This was a sensitivity study aiming to provide information relative to the magnitude of differences when a more realistic aerosol extinction profile is used instead of a theoretical profile, and to explain the mechanisms that are responsible for the differences
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