Evaluation of ECMWF HRES IFS and CAMS IFS intra- and day-ahead forecasts with respect to surface solar irradiances

Abstract

The main focus of the CAMS Radiation Service is to provide high-quality long-term historical irradiance data which is easily integrated in solar resource assessments and other related studies. At the same time, the CAMS system provides a forecast of atmospheric conditions, that is, aerosols, water vapor and ozone. As part of its Integrated Forecasting System (IFS), ECMWF generates an alternative forecast which uses additional modules based on the atmospheric conditions forecasted by CAMS, which we name the CAMS IFS forecast (Inness et al., 2015). It is an overarching question, whether the CAMS IFS forecast provides radiation forecasts in a similar or better quality as the operational HRES IFS forecast and whether it could be implemented as an operational product on itself. The IFS CAMS forecast is operated on a low spatial resolution of 40 km (~ 3.5°). This is coarse compared to the 9 km (~0.1°) spatial resolution of the operational HRES IFS, but the CAMS IFS runs are based on additional aerosol forecasts provided by CAMS while the operational ECMWF IFS runs use an aerosol climatology (Bozzo et al., 2017). The present evaluation is done for the full year 2021 on a global scale using ground observations from well-known research quality solar radiation measurement networks (BSRN, SOLRAD, SURFRAD, enerMENA, NREL-MIDC). Following solar energy stakeholders needs, this evaluation will be concentrated on the intraday and day-ahead range, that is, the evaluation will use the forecasts up to 48 hours. The forecasts are obtained from the run at 0 UTC which ensures that the forecasts are available for all intraday and day ahead market transactions and operational processes. Both forecasts sources have a native time resolution of 1 hour in their public accessible output, therefore, the evaluation is also performed on an hourly resolution basis.