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Routine measurements of the beam irradiance at normal incidence include theirradiance originating from within the extent of the solar disc only(DNIS), whose angular extent is 0.266° ± 1.7 %, and from a larger circumsolar region, called the circumsolar normalirradiance (CSNI). This study investigates whether the spectral aerosol opticalproperties of the AERONET stations are sufficient for an accurate modellingof the monochromatic DNIS and CSNI under cloud-free conditions in adesert environment. The data from an AERONET station in Abu Dhabi, UnitedArab Emirates, and the collocated Sun and Aureole Measurement instrument whichoffers reference measurements of the monochromatic profile of solarradiance were exploited. Using the AERONET data both the radiative transfermodels libRadtran and SMARTS offer an accurate estimate of the monochromaticDNIS, with a relative root mean square error (RMSE) of 6 % and acoefficient of determination greater than 0.96. The observed relative biasobtained with libRadtran is +2 %, while that obtained with SMARTS is−1 %. After testing two configurations in SMARTS and three in libRadtranfor modelling the monochromatic CSNI, libRadtran exhibits the most accurateresults when the AERONET aerosol phase function is presented as a two-termHenyey–Greenstein phase function. In this case libRadtran exhibited arelative RMSE and a bias of respectively 27 and −24 % and acoefficient of determination of 0.882. Therefore, AERONET data may very wellbe used to model the monochromatic DNIS and the monochromatic CSNI. Theresults are promising and pave the way towards reporting the contribution ofthe broadband circumsolar irradiance to standard measurements of the beamirradiance

Can AERONET data be used to accurately model the monochromatic beam and circumsolar irradiances under cloud-free conditions in desert environment?