{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,11,13]],"date-time":"2025-11-13T06:36:35Z","timestamp":1763015795209,"version":"build-2065373602"},"reference-count":49,"publisher":"MDPI AG","issue":"2","license":[{"start":{"date-parts":[[2020,5,16]],"date-time":"2020-05-16T00:00:00Z","timestamp":1589587200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Forecasting"],"abstract":"<jats:p>Direct Normal Irradiance (DNI) predictions obtained from the Integrated Forecasting System of the European Centre for Medium-Range Weather Forecast (IFS\/ECMWF) were compared against ground-based observational data for one location at the south of Portugal (\u00c9vora). Hourly and daily DNI values were analyzed for different temporal forecast horizons (1 to 3 days ahead) and results show that the IFS\/ECMWF slightly overestimates DNI for the period of analysis (1 August 2018 until 31 July 2019) with a fairly good agreement between model and observations. Hourly basis evaluation shows relatively high errors, independently of the forecast day. Root mean square error increases as the forecast time increases with a relative error of ~45% between the first and the last forecast. Similar patterns are observed in the daily analysis with comparable magnitude errors. The correlation coefficients between forecast and observed data are above 0.7 for both hourly and daily data. A methodology based on a new DNI attenuation Index (DAI) was developed to estimate cloud fraction from hourly values integrated over a day and, with that, to correlate the accuracy of the forecast with sky conditions. This correlation with DAI reveals that in IFS\/ECMWF model, the atmosphere as being more transparent than reality since cloud cover is underestimated in the majority of the months of the year, taking the ground-based measurements as a reference. The use of the DAI estimator confirms that the errors in IFS\/ECMWF are larger under cloudy skies than under clear sky. The development and application of a post-processing methodology improves the DNI predictions from the IFS\/ECMWF outputs, with a decrease of error of the order of ~30%, when compared with raw data.<\/jats:p>","DOI":"10.3390\/forecast2020007","type":"journal-article","created":{"date-parts":[[2020,5,20]],"date-time":"2020-05-20T10:37:38Z","timestamp":1589971058000},"page":"130-150","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":6,"title":["Assessment of Direct Normal Irradiance Forecasts Based on IFS\/ECMWF Data and Observations in the South of Portugal"],"prefix":"10.3390","volume":"2","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-2845-6718","authenticated-orcid":false,"given":"Jo\u00e3o","family":"Perdig\u00e3o","sequence":"first","affiliation":[{"name":"Instituto de Ci\u00eancias da Terra, Universidade de \u00c9vora, Rua Rom\u00e3o Ramalho 59, 7000-671 \u00c9vora, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6210-1964","authenticated-orcid":false,"given":"Paulo","family":"Canhoto","sequence":"additional","affiliation":[{"name":"Instituto de Ci\u00eancias da Terra, Universidade de \u00c9vora, Rua Rom\u00e3o Ramalho 59, 7000-671 \u00c9vora, Portugal"},{"name":"Departamento de F\u00edsica, Escola de Ci\u00eancias e Tecnologia, Universidade de \u00c9vora, Rua Rom\u00e3o Ramalho 59, 7000-671 \u00c9vora, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-1311-6291","authenticated-orcid":false,"given":"Rui","family":"Salgado","sequence":"additional","affiliation":[{"name":"Instituto de Ci\u00eancias da Terra, Universidade de \u00c9vora, Rua Rom\u00e3o Ramalho 59, 7000-671 \u00c9vora, Portugal"},{"name":"Departamento de F\u00edsica, Escola de Ci\u00eancias e Tecnologia, Universidade de \u00c9vora, Rua Rom\u00e3o Ramalho 59, 7000-671 \u00c9vora, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-2981-2232","authenticated-orcid":false,"given":"Maria Jo\u00e3o","family":"Costa","sequence":"additional","affiliation":[{"name":"Instituto de Ci\u00eancias da Terra, Universidade de \u00c9vora, Rua Rom\u00e3o Ramalho 59, 7000-671 \u00c9vora, Portugal"},{"name":"Departamento de F\u00edsica, Escola de Ci\u00eancias e Tecnologia, Universidade de \u00c9vora, Rua Rom\u00e3o Ramalho 59, 7000-671 \u00c9vora, Portugal"}]}],"member":"1968","published-online":{"date-parts":[[2020,5,16]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"706","DOI":"10.1016\/j.rser.2014.07.041","article-title":"The near future availability of photovoltaic energy in Europe and Africa in climate-aerosol modeling experiments","volume":"38","author":"Gaetani","year":"2014","journal-title":"Renew. Sustain. Energy Rev."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"139","DOI":"10.1016\/j.solener.2015.08.034","article-title":"Estimating the potential for solar energy utilization in Chile by satellite-derived data and ground station measurements","volume":"121","author":"Escobar","year":"2015","journal-title":"Sol. Energy"},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"68","DOI":"10.1016\/j.renene.2014.09.026","article-title":"Projected changes in wind energy potentials over Iberia","volume":"75","author":"Santos","year":"2015","journal-title":"Renew. Energy"},{"key":"ref_4","unstructured":"Heiselberg, P.K. (2016, January 22\u201325). Creating localised near future weather data for predicting the performance of buildings in the UK. Proceedings of the 12th REHVA World Congress CLIMA 2016, Aalborg, Denmark."},{"key":"ref_5","unstructured":"Ruiz-Arias, J.A., Gueymard, C.A., Dudhia, J., and Pozo-Vazquez, D. (2012, January 13\u201317). Improvement of the weather research and forecasting (WRF) model for solar resource assessments and forecasts under clear skies. Proceedings of the World Renewable Energy Forum, Denver, CO, USA."},{"key":"ref_6","doi-asserted-by":"crossref","unstructured":"Perdig\u00e3o, J., Salgado, R., Magarreiro, C., Soares, P.M.M., Costa, M.J., and Dasari, H. (2017). An Iberian climatology of solar radiation obtained from WRF regional climate simulations for 1950\u20132010 period. Atmos. Res.","DOI":"10.1016\/j.atmosres.2017.08.016"},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"411","DOI":"10.1016\/j.solener.2014.12.011","article-title":"Optimal combination of gridded and ground-observed solar radiation data for regional solar resource assessment","volume":"112","author":"Gueymard","year":"2015","journal-title":"Sol. Energy"},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"1295","DOI":"10.1016\/j.solener.2006.12.007","article-title":"Potential of solar electricity generation in the European Union member states and candidate countries","volume":"81","author":"Huld","year":"2007","journal-title":"Sol. Energy"},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"387","DOI":"10.1016\/j.solener.2019.04.070","article-title":"Development of an ANN based corrective algorithm of the operational ECMWF global horizontal irradiation forecasts","volume":"185","author":"Pereira","year":"2019","journal-title":"Sol. Energy"},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"1772","DOI":"10.1016\/j.solener.2010.07.002","article-title":"Prediction of global solar irradiance based on time series analysis: Application to solar thermal power plants energy production planning","volume":"84","author":"Zarzalejo","year":"2010","journal-title":"Sol. Energy"},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"1343","DOI":"10.1016\/j.agrformet.2009.03.005","article-title":"A comparative study of ordinary and residual kriging techniques for mapping global solar radiation over southern Spain","volume":"149","author":"Alsamamra","year":"2009","journal-title":"Agric. For. Meteorol."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"244","DOI":"10.1016\/j.solener.2013.04.012","article-title":"Economic Merits of a State-of-the-Art Concentrating Solar Power Forecasting System for Participation in the Spanish Electricity Market","volume":"93","author":"Kraas","year":"2013","journal-title":"Sol. Energy"},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"287","DOI":"10.1016\/j.solener.2014.07.008","article-title":"Direct normal irradiance forecasting and its application to concentrated solar thermal output forecasting\u2014A review","volume":"108","author":"Law","year":"2014","journal-title":"Sol. Energy"},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"866","DOI":"10.1016\/j.renene.2015.08.068","article-title":"Day-ahead resource forecasting for concentrated solar power integration","volume":"86","author":"Nonnenmacher","year":"2016","journal-title":"Renew. Energy"},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"770","DOI":"10.3390\/en5030770","article-title":"Analysis and prediction of energy production in concentrating photovoltaic (CPV) installations","volume":"5","author":"Wang","year":"2012","journal-title":"Energies"},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"1595","DOI":"10.1175\/JAMC-D-16-0297.1","article-title":"Postprocessing Methodology for Direct Normal Irradiance Forecasting Using Cloud Information and Aerosol Load Forecasts","volume":"56","author":"Revuelta","year":"2017","journal-title":"J. Appl. Meteorol. Climatol."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"14","DOI":"10.1016\/j.solener.2018.05.039","article-title":"Short-term forecasts of GHI and DNI for solar energy systems operation: Assessment of the ECMWF integrated forecasting system in southern Portugal","volume":"170","author":"Lopes","year":"2018","journal-title":"Sol. Energy"},{"key":"ref_18","first-page":"317","article-title":"Evaluation of DNI forecast based on the WRF mesoscale atmospheric model for CPV applications","volume":"1477","author":"Gueymard","year":"2012","journal-title":"AIP Conf. Proc.-Am. Inst. Phys."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"2571","DOI":"10.1175\/JAMC-D-14-0074.1","article-title":"Skill of direct solar radiation predicted by the ECMWF global atmospheric model over Australia","volume":"53","author":"Troccoli","year":"2014","journal-title":"J. Appl. Meteorol. Climatol."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"3519","DOI":"10.1016\/j.solener.2012.03.010","article-title":"Using direct normal irradiance models and utility electrical loading to assess benefit of a concentrating solar power plant","volume":"86","author":"Vick","year":"2012","journal-title":"Sol. Energy"},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"2720","DOI":"10.1175\/MWR-D-11-00301.1","article-title":"Intercomparison of global model precipitation forecast skill in 2010\/11 using the SEEPS score","volume":"140","author":"Haiden","year":"2012","journal-title":"Mon. Weather Rev."},{"key":"ref_22","unstructured":"(2019, September 15). Kipp & Zonen. Available online: http:\/\/www.kippzonen.com\/."},{"key":"ref_23","unstructured":"World Meteorological Organization (WMO) (2008). Guide to Meteorological Instruments and Methods of Observation, (WMO-No. 8), World Meteorological Organization (WMO). [7th ed.]."},{"key":"ref_24","unstructured":"ISO (1990). ISO 9060:1990: Specification and Classification of Instruments for Measuring Hemispherical Solar and Direct Solar Radiation, ISO."},{"key":"ref_25","first-page":"8542","article-title":"BSRN Global Network recommended QC tests, V2","volume":"25","author":"Long","year":"2010","journal-title":"J. Clim."},{"key":"ref_26","unstructured":"Hogan, R.J., and Bozzo, A. (2016). ECRAD: A new radiation scheme for the IFS. ECMWF Tech. Memo., 787."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"4773","DOI":"10.1175\/2008MWR2363.1","article-title":"Impact of a new radiation package, mcrad, in the ecmwf integrated forecasting system","volume":"136","author":"Morcrette","year":"2008","journal-title":"Mon. Weather Rev"},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"23895","DOI":"10.1029\/97JD01864","article-title":"Contribution of different aerosol species to the global aerosol extinction optical thickness: Estimates from model results","volume":"102","author":"Tegen","year":"1997","journal-title":"J. Geophys. Res."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"1945","DOI":"10.5194\/acp-17-1945-2017","article-title":"The CAMS interim reanalysis of carbon monoxide, ozone and aerosol for 2003\u20132015","volume":"17","author":"Flemming","year":"2017","journal-title":"Atmos. Chem. Phys."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"2058","DOI":"10.1175\/1520-0442(1996)009<2058:AAPOTS>2.0.CO;2","article-title":"An accurate parameterization of the solar radiative properties of cirrus clouds","volume":"9","author":"Fu","year":"1996","journal-title":"J. Clim."},{"key":"ref_31","unstructured":"(2019, August 25). European Center for Medium Time Weather Forecasting (ECMWF). Available online: www.ecmwf.int."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"1671","DOI":"10.1007\/s00382-010-0939-3","article-title":"Assessment of global dimming and brightening in IPCC-AR4\/CMIP3 models and ERA-40","volume":"37","author":"Wild","year":"2011","journal-title":"Clim. Dyn."},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"305","DOI":"10.1016\/j.solener.2013.05.005","article-title":"Comparison of numerical weather prediction solar irradiance forecasts in the US, Canada and Europe","volume":"94","author":"Perez","year":"2013","journal-title":"Sol. Energy"},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"1247","DOI":"10.5194\/gmd-7-1247-2014","article-title":"Root mean square error (RMSE) or mean absolute error (MAE)?\u2014Arguments against avoiding RMSE in the literature","volume":"7","author":"Chai","year":"2014","journal-title":"Geosci. Model Dev."},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"39","DOI":"10.5194\/asr-15-39-2018","article-title":"Short-range solar radiation forecasts over Sweden","volume":"15","author":"Landelius","year":"2018","journal-title":"Adv. Sci. Res."},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"885","DOI":"10.13031\/2013.23153","article-title":"Model evaluation guidelines for systematic quantification of accuracy in watershed simulations","volume":"50","author":"Moriasi","year":"2007","journal-title":"Trans. ASABE"},{"key":"ref_37","unstructured":"Iqbal, M. (1975). An Introduction to Solar Radiation, Academic Press."},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"1059","DOI":"10.5194\/amt-12-1059-2019","article-title":"A cloud identification algorithm over the Arctic for use with AATSR\u2013SLSTR measurements","volume":"12","author":"Jafariserajehlou","year":"2019","journal-title":"Atmos. Meas. Tech."},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"853","DOI":"10.1175\/1520-0477(1996)077<0853:CATERE>2.0.CO;2","article-title":"Clouds and the Earth\u2019s Radiant Energy System (CERES): An earth observing system experiment","volume":"77","author":"Wielicki","year":"1996","journal-title":"Bull. Am. Meteorol. Soc."},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"238","DOI":"10.1016\/j.renene.2015.02.031","article-title":"Correcting satellite derived DNI with systematic and seasonal deviations: Application to India","volume":"80","author":"Polo","year":"2015","journal-title":"Renew. Energy"},{"key":"ref_41","doi-asserted-by":"crossref","first-page":"610","DOI":"10.1016\/j.solener.2018.01.094","article-title":"Conditional summertime day-ahead solar irradiance forecast","volume":"163","author":"Mejia","year":"2018","journal-title":"Sol. Energy"},{"key":"ref_42","doi-asserted-by":"crossref","first-page":"25","DOI":"10.1016\/j.solener.2016.03.001","article-title":"Preliminary survey on site-adaptation techniques for satellite-derived and reanalysis solar radiation datasets","volume":"132","author":"Polo","year":"2016","journal-title":"Sol. Energy"},{"key":"ref_43","doi-asserted-by":"crossref","first-page":"246","DOI":"10.1016\/j.solener.2013.11.010","article-title":"Verification of the SUNY direct normal irradiance model with ground measurements","volume":"99","author":"Nonnenmacher","year":"2014","journal-title":"Sol. Energy"},{"key":"ref_44","doi-asserted-by":"crossref","unstructured":"Pan, J.-S., Polycarpou, M., Wozniak, M., Carvalho, A.P.L.F., Quintian, H., and Corchado, E. (2013). Support vector forecasting of solar radiation values. Hybrid Artificial Intelligent Systems, Springer.","DOI":"10.1007\/978-3-642-40846-5"},{"key":"ref_45","doi-asserted-by":"crossref","first-page":"3669","DOI":"10.1080\/01431161.2017.1302111","article-title":"Assessment of surface solar irradiance retrieved by CERES","volume":"38","author":"Almorox","year":"2017","journal-title":"Int. J. Remote Sens."},{"key":"ref_46","doi-asserted-by":"crossref","first-page":"1716","DOI":"10.1002\/joc.5914","article-title":"Spatio-temporal variations of cloud fraction based on circulation types in the Iberian Peninsula","volume":"39","author":"Lorenzo","year":"2019","journal-title":"Int. J. Climatol."},{"key":"ref_47","unstructured":"Lopes, M. (2015). Desenvolvimento de um Sistema de Baixo custo para a Previs\u00e3o da Irradi\u00e2ncia Solar a Curto Prazo. [Master\u2019s Thesis, Instituto Superior T\u00e9cnico]. Available online: https:\/\/fenix.tecnico.ulisboa.pt\/downloadFile\/281870113702447\/Dissertacao_67932."},{"key":"ref_48","first-page":"D00D09","article-title":"Dimming\/brightening over the Iberian Peninsula: Trends in sunshine duration and cloud cover and their relations with atmospheric circulation","volume":"114","author":"Brunetti","year":"2009","journal-title":"J. Geophys. Res."},{"key":"ref_49","first-page":"3","article-title":"Seasonal analysis of cloud characteristics and radiative effect over the Iberian Peninsula using MODIS-CERES observations","volume":"14","author":"Utrillas","year":"2017","journal-title":"Tethys"}],"container-title":["Forecasting"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2571-9394\/2\/2\/7\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T09:29:35Z","timestamp":1760174975000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2571-9394\/2\/2\/7"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2020,5,16]]},"references-count":49,"journal-issue":{"issue":"2","published-online":{"date-parts":[[2020,6]]}},"alternative-id":["forecast2020007"],"URL":"https:\/\/doi.org\/10.3390\/forecast2020007","relation":{},"ISSN":["2571-9394"],"issn-type":[{"type":"electronic","value":"2571-9394"}],"subject":[],"published":{"date-parts":[[2020,5,16]]}}}