Note on Mixed-Layer Entrainment Closure

Abstract

The entrainment closure for the turbulence energy budgetcommonly used in unsaturated mixed layer models is re-derivedfrom the perspective of potential energy changes, and it isconcluded that the correct physical interpretation of theenergetics based on experimental evidence is that the turbulenceform entrainment at about the 20% efficiency level(not the 4% level). In the case of a cloud-toppedmixed layer, this physical interpretation leads to are-examination of the condition for stratocumulus cloud-topentrainment instability and the conclusion that recentcorrections for liquid water loading may yet be toorestrictive.