New Insights into Cloud Entrainment Processes
As a cloud grows, air outside the cloud is entrained, or drawn into the cloud due to turbulent motions at cloud boundaries. The amount and characteristics of the entrained environmental air, which is generally much drier than the cloudy air, impact the cloud’s growth and microphysical properties. Therefore, the entrainment rate is an important parameter that needs to be better understood to improve climate model simulations. U.S. Department of Energy researchers implemented a new method, in which individual particles in a high-resolution model simulation are tracked, to study the cloud entrainment process. The new method produces higher entrainment rates in convective clouds than previous methods because it is able to track the fast recycling of air into and out of the cloud that other methods could not. Over half of the air entrained by the simulated cloud was found to have been previously resident in the cloud, indicating that assumptions about the thermodynamic properties of entrained air may need to be revisited.
Yeo, K., and D. M. Romps. 2013. “Measurement of Convective Entrainment Using Lagrangian Particles,” Journal of the Atmospheric Sciences 70, 266-77. DOI: 10.1175/JAS-D-12-0144.1.