What causes mammatus?

To address some of the most likely formation mechanisms of mammatus, high-resolution, idealized numerical modeling experiments of portions of cumulonimbus anvils initialized with soundings taken in the vicinity of observed mammatus were performed. These simulations were believed to be the first to model mammatus-like clouds explicitly. A second proposed mechanism, cloud-base detrainment instability (CDBI), was also tested. Evidence was obtained that the CBDI criterion is a necessary, but not sufficient, condition for mammatus formation.