Mixing between shallow cumulus clouds and their environment is studied using large eddy-simulations. The origin of in-cloud air is studied by two distinct methods: ﬁrstly by analyzing conserved variable mixing diagrams (Paluch diagrams), and secondly by tracing back cloud-air parcels represented by massless Lagrangian particles that follow the ﬂow. The obtained Paluch diagrams are found to be similar to many results found in literature, but the source of entrained air found by particle tracking deviates from the source inferred from the Paluch analysis. Whereas the classical Paluch analysis seems to provide some evidence for cloud-top mixing, particle tracking shows that virtually all mixing occurs laterally. Particle trajectories averaged over the entire cloud ensemble also clearly indicate the absence of signiﬁcant cloud top mixing in shallow cumulus clouds.
T Heus, G van Dijk, HJJ Jonker, HEA van den Akker. Mixing in shallow cumulus clouds studied by Lagrangian particle tracking
published, J. Atmos. Sci., 2008, 65