Stratocumulus clouds are ubiquitous around the globe. Wide-spread presence, persistence and high albedo makes them important for the energy balance of the planet. Typically, they occupy upper few hundred meters of the atmospheric boundary layer over subtropical and midlatitude oceans. Circulation and turbulence in such a stratocumulus-topped boundary layer (STBL) transport moisture from the ocean surface maintaining the cloud against entrainment drying. However, when the STBL grows in depth, the drivers of the circulation weaken or the subcloud layer stabilizes, the mixing across the entire STBL depth may become impossible to sustain. The boundary layer decouples, i.e. the stratocumulus cloud is disconnected from the moisture supply from the surface, with important implications for its further evolution.
Within the present study, the properties of turbulence (such as turbulence kinetic energy dissipation rate, turbulent heat fluxes, inertial range scaling, anisotropy, length scales) are compared between coupled and decoupled STBLs using high resolution in situ measurements performed by the helicopter-borne platform ACTOS in the region of the Eastern North Atlantic. Particular attention is given to small-scale features, deviations from the assumption of stationary homogeneous isotropic turbulence and differences between the sublayers of the decoupled STBL.