Tornado Environment Frequency Trends (IMAGE) Northern Illinois University Caption This is a graphic representation of tornado environment frequency trends. Credit Adapted by NIU from npj Climate and Atmospheric Science, Gensini/Brooks 2018 (http://creativecommons. org/licenses/by/4.0/) Usage Restrictions Please use credit License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.