Comparison between Measurements and Model Simulations of Solar Radiation at a High Altitude Site: Case Studies for the Izana BSRN Station

In this work we have carried out a comparative study of shortwave downward radiation (SDR) measurements and simulations obtained with the radiative transfer model (RTM) LibRadtran in order to be used as a model quality control at Izana BSRN (Baseline Surface Radiation Network). We selected cases corresponding to the most common atmospheric conditions at the Izana station (IZA), we analyzed: clear-sky and African dust intrusions. The input parameters for the model, such as a total ozone column, surface albedo, water vapour column and aerosols parameters, were measured at IZA. The results of the two clear-sky case studies (16 May and 26 October 2010) analyzed here show an underestimation of the simulations for the SDR global and direct for solar zenith angles (SZA) lower than 70 degrees. The maximum relative differences for SDR global, direct and diffuse are 6%, 2% and 6%, respectively. For dust intrusion case studies (22 July 2009 and 10 July 2010) and for SZA lower than 70 degrees, the simulations of the direct normal component are slightly overestimated. For the SDR global, direct and diffuse components, the maximum relative differences are 1%, -1% and 8% for 22 July 2009 respectively, and 5%, 4% and 3% for 10 July 2010. The overall results of the RMSE for the global direct and diffuse components are 3%, 10% and 4% and 2%, 3% and 5% for both atmospheric situations. These results show a reasonably good agreement between simulations and measurements.