Do stratocumulus clouds detrain? FIRE I data revisited.

Analyses of aircraft observations collected in stratocumulus-topped boundary layers during the First ISCCP (International Satellite Cloud Climatology Project) Regional Experiment (FIRE I) show the frequent presence of clear, but relatively moist air patches near the stratocumulus cloud top interface. A conditional sampling of measurements in these clear air patches shows that their thermodynamic properties do more resemble boundary-layer air characteristics than that of free troposphere air. From an aircraft leg through cloud tops it is demonstrated that turbulent mixing across the cloud-top interface can lead to the local dissipation of the cloud top. Analogous to the terminology used for shallow cumulus parameterizations this process can be considered as detrainment, with which we mean that after a mixing event across the cloud top boundaries, mixed unsaturated parcels become part of the clear environment of the cloud.