A line of convection embedded in a stratocumulus-topped boundary layer

Abstract

During the Southern Ocean Cloud Experiment a line of convection embedded in an otherwise homogeneous stratocumulus layer was sampled at four levels by means of an instrumented aircraft. At the lower levels there was an abrupt change in microphysical and thermodynamic properties from the updraught region to the environment. At the upper level the change was more gradual and extended over a larger region, indicating the spreading out of the convective region underneath the strong inversion capping the boundary layer. Precipitation was observed at all levels, even in the convective region except near its centre core. Vertical-velocity fluctuations in the convective region near the inversion were indistinguishable from the surroundings. At these high levels the horizontal wind in the convective region was from the same direction as the air close to the surface, but was at an angle of up to 60° with the horizontal wind from the surroundings. the convective region was characterized by cloud droplet concentrations that were often more than double those recorded in the surrounding cloud. This indicates that the modifications to the cloud droplet spectra associated with the onset of precipitation starts in the convective region and is enhanced in the stratiform region.