Entrainment in Resolved, Dry Thermals

Understand

Entrainment in cumulus convection remains ill-understood and difficult to quantify.

• For instance, entrainment is widely believed to be a fundamentally turbulent process, even though Turner (1957) pointed out that dry thermals entrain primarily because of buoyancy (via a dynamical constraint requiring an increase in radius $r$), rather than turbulence.
• Furthermore, entrainment has been postulated to obey a $1/r$ scaling, but this scaling has not been firmly established.
• Here, we study the classic case of dry, turbulent thermals in a neutrally stratified environment using fully resolved direct numerical simulation.