The Influence of Successive Thermals on Entrainment and Dilution in a Simulated Cumulus Congestus

Cumulus clouds are frequently observed as comprising multiple successive thermals, yet numerical simulations of entrainment have not investigated this level of detail. Here, an idealized simulated cumulus congestus consisting of three successive thermals is used to analyze and understand their role in maintaining the high liquid water content in the core of the cloud, which past 1D modeling studies have suggested can ultimately determine its ability to precipitate. Entrainment and detrainment are calculated directly at the edge of the cloud core at frequent time intervals. Entrainment maxima occur at the rear of the toroidal circulation associated with each thermal and thus are transient features in the lifetime of multithermal clouds. The evolution of the least diluted parcels within each thermal shows that the entrainment rates alone cannot predict the erosion of the high liquid water content cores. A novel analysis of samples of entrained and detrained air within each successive thermal illustrates tendencies for even positively buoyant air, containing condensate, to be entrained by later thermals that rise in the wakes of their predecessors, limiting their dilution. The later thermals can achieve greater depths and produce precipitation when a single thermal could not. Future work is yet needed to evaluate the generality of these results using multiple clouds simulated in different environments with less-idealized modeling frameworks. Implications for current cumulus parameterizations are briefly discussed.

Icing on a Non-Rotating Cylinder Under Conditions of High Liquid Water Content in the Air: I. Form and Size of Ice Deposits

Ice accretion on a non-rotating cylinder was studied under icing conditions involving a wet-growth (glaze) process. Experiments were performed in an outdoor wind tunnel designed for icing studies. In this paper, the experimental method is introduced and the characteristics of form, size, and time development of deposits are given. In terms of freezing conditions, these characteristics were found to be very complex, in which all the external effects: air temperature, wind conditions, liquid water content in the air, and accretion time, are of the same order of importance. In a wet-growth process there exists above the icing surface a water film, the behaviour and dynamics of which are affected by various variables. The water film seems to play an important role in the wet-growth icing.

Icing on a Non-Rotating Cylinder Under Conditions of High Liquid Water Content in the Air: I. Form and Size of Ice Deposits

Ice accretion on a non-rotating cylinder was studied under icing conditions involving a wet-growth (glaze) process. Experiments were performed in an outdoor wind tunnel designed for icing studies. In this paper, the experimental method is introduced and the characteristics of form, size, and time development of deposits are given. In terms of freezing conditions, these characteristics were found to be very complex, in which all the external effects: air temperature, wind conditions, liquid water content in the air, and accretion time, are of the same order of importance. In a wet-growth process there exists above the icing surface a water film, the behaviour and dynamics of which are affected by various variables. The water film seems to play an important role in the wet-growth icing.