Cumulonimbus clouds.jpg (IMAGE) Durham University Caption Cumulonimbus clouds over Chandler, Arizona, USA, in 2018, showing the inverted pyramid with the dark cloud beneath. Credit Mircea Goia Usage Restrictions Must be credited as in the credit information provided. 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.