Cloud transitions and decoupling in shear‐free stratocumulus‐topped boundary layers

Large‐eddy simulations of shear‐free stratocumulus‐topped layers tend strongly toward a two‐layer structure as the negative area in the buoyancy flux profile that would be necessary to maintain a mixed layer increases to more than 10% of the positive area. In addition to identifying a threshold for what amounts to a convective transition, the simulations provide further evidence that a commonly used entrainment closure is ill‐founded. Lastly the simulations demonstrate that attempts to formulate a similarity theory for convective layers must account for the geometry of the buoyancy‐flux profile, and not simply its integral.