Entrainment zone
From Glossary of Meteorology
entrainment zone
(Also called entrainment layer.) A layer of intermittent turbulence and overshooting thermals at the top of the convective mixed layer where the free atmosphere is entrained into the top of the boundary layer.
The entrainment zone is thinner when a stronger temperature inversion caps the boundary layer and thicker when turbulence and thermals are more vigorous.