{"id":2321,"date":"2020-05-18T11:02:21","date_gmt":"2020-05-18T11:02:21","guid":{"rendered":"http:\/\/www.icterra.pt\/?p=2321"},"modified":"2020-05-18T11:02:21","modified_gmt":"2020-05-18T11:02:21","slug":"assessment-of-direct-normal-irradiance-forecasts-based-on-ifs-ecmwf-data-and-observations-in-the-south-of-portugal","status":"publish","type":"post","link":"https:\/\/www.icterra.pt\/legacy\/index.php\/2020\/05\/18\/assessment-of-direct-normal-irradiance-forecasts-based-on-ifs-ecmwf-data-and-observations-in-the-south-of-portugal\/","title":{"rendered":"Assessment of Direct Normal Irradiance Forecasts Based on IFS\/ECMWF Data and Observations in the South of Portugal"},"content":{"rendered":"<p><span style=\"font-family: arial, helvetica, sans-serif; font-size: 12pt;\"><span class=\"inlineblock\">Jo\u00e3o Perdig\u00e3o, <\/span><span class=\"inlineblock\">Paulo Canhoto, <\/span><span class=\"inlineblock\">Rui Salgado and <\/span><span class=\"inlineblock\">Maria Jo\u00e3o Costa<sup><br \/>\n<\/sup><\/span><\/span><\/p>\n<p style=\"text-align: justify;\">\n<p style=\"text-align: justify;\"><strong><span style=\"font-family: arial, helvetica, sans-serif; font-size: 12pt;\">Assessment of Direct Normal Irradiance Forecasts Based on IFS\/ECMWF Data and Observations in the South of Portugal<\/span><\/strong><\/p>\n<div class=\"target-item custom-accordion-for-small-screen-content \">\n<div class=\"art-abstract in-tab hypothesis_container\" style=\"text-align: justify;\"><span style=\"font-family: arial, helvetica, sans-serif; font-size: 12pt;\">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.<\/span><\/div>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>Jo\u00e3o Perdig\u00e3o, Paulo Canhoto, Rui Salgado and Maria Jo\u00e3o Costa Assessment of Direct Normal Irradiance Forecasts Based on IFS\/ECMWF Data and Observations in the South of Portugal 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 [&hellip;]<\/p>\n","protected":false},"author":3,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[16],"tags":[366,362,365,364,363],"_links":{"self":[{"href":"https:\/\/www.icterra.pt\/legacy\/index.php\/wp-json\/wp\/v2\/posts\/2321"}],"collection":[{"href":"https:\/\/www.icterra.pt\/legacy\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.icterra.pt\/legacy\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.icterra.pt\/legacy\/index.php\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/www.icterra.pt\/legacy\/index.php\/wp-json\/wp\/v2\/comments?post=2321"}],"version-history":[{"count":1,"href":"https:\/\/www.icterra.pt\/legacy\/index.php\/wp-json\/wp\/v2\/posts\/2321\/revisions"}],"predecessor-version":[{"id":2322,"href":"https:\/\/www.icterra.pt\/legacy\/index.php\/wp-json\/wp\/v2\/posts\/2321\/revisions\/2322"}],"wp:attachment":[{"href":"https:\/\/www.icterra.pt\/legacy\/index.php\/wp-json\/wp\/v2\/media?parent=2321"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.icterra.pt\/legacy\/index.php\/wp-json\/wp\/v2\/categories?post=2321"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.icterra.pt\/legacy\/index.php\/wp-json\/wp\/v2\/tags?post=2321"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}