Circumsolar Irradiance Modelling Using LibRadtran and AERONET Data

Abstract

In this work, the monochromatic circumsolar irradiance (at 675 nm) is modelled using libRadtran and AERONET data at Évora, Portugal, for selected cases representing the 1st, 25th, 50th and 75th percentiles of the aerosol optical depth (AOD) measurements distribution at 675 nm and a maximum value of AOD registered during a Saharan dust outbreak in February 2017. Since there are no measurements of circumsolar irradiance at Évora, the assessment of the model output accuracy was done through a comparison of both the modelled DNI from the solar disk only and the DNI including the circumsolar contribution against measurements from a pyrheliometer included in a meteorological station installed at the same location. The mean bias error and the root mean square error were found to be lower for the DNI with the circumsolar contribution, thus validating the modelling approach of circumsolar irradiance.