The Entrainment Mechanism in Colorado Cumuli

Abstract

Cloud air and clear air properties are analyzed to determine the altitude from where the entrained air originates. This is done using two parameters that are conserved with adiabatic altitude changes and that mix in a nearly linear manner. The method employed is only applicable to cloud regions that do not contain significant amounts of ice or precipitation size drops. The analysis shows that most of the entrained air originates several kilometers above the observation level. The mixed regions are typically found in downdrafts and the weaker updraft regions. The present results are inconsistent with the laterally entraining plume model. The results indicate that mixing of dry environmental air with cloud air produces sufficient evaporative cooling to create downdrafts that penetrate several kilometers into the cloud. The updraft air is diluted primarily through mixing with nearby downdraft air.