Organization of a Plume Ensemble

Brian Mapes University of Miami

Category: Modeling

Working Group: Cloud Life Cycle

In order to ameliorate some shortcomings of convection schemes based on a single plume, or on an ensemble of plumes that compete for instability in their common large-scale column, we describe a treatment in which plumes can interact. The index of the ensemble is called a plume’s generation. First-generation plumes mix their way up in the mean large-scale environment, detraining some mass flux along the way. The detrained mass tends to have greater moisture and entropy than ambient air, so higher-generation plumes that entrain it gain an advantage in their buoyancy and thus vertical growth. The succession is terminated when additional plumes do not reach higher altitudes (typically just a few generations). The closure for this plume ensemble therefore involves an interaction probability, which we treat via a single scalar: the “organization” of the cumulus cloud field (denoted org). The paper first describes single-column tests using the Bretherton et al. (2004) entraining-detraining plume, plus specified cooling and simple surface-flux and mixed-layer treatments. Plume interaction allows shallow and deep plumes to coexist with the same specified lateral-mixing strength. When org is defined functionally as a linear ramp from random (org=0) to maximum plume overlap (org = 1), varying org causes the mix of shallower and deep plumes to vary. With robust lateral mixing, the first generation has significant sensitivity to environmental dryness, yet late-generation plumes in high-org conditions can reach tropopause altitudes without such severe dilution.

This poster will be displayed at ASR Science Team Meeting.