Abstract
Abstract Precipitation-driven downdrafts are an important component of deep convective systems. They stabilize the atmosphere by injecting relatively cold and dry air into the boundary layer. They have also been invoked as responsible for balancing surface latent and sensible heat fluxes in the heat and moisture budget of tropical boundary layers. This study is focused on precipitation-driven downdrafts and basic aspects of their dynamics in a case of radiative–convective equilibrium. Using Lagrangian particle tracking, it is shown that such downdrafts have very low initial heights, with most parcels originating within 1.5 km from the surface. The tracking is also used to compute the contribution of downdrafts to the flux of moist static energy at the top of the boundary layer, and it is found that this is on the same order of magnitude as the contribution due to convective updrafts, but much smaller than that due to turbulent mixing across the boundary layer top in the environment. Furthermore, considering the mechanisms driving the downdrafts, it is shown that the work done by rain evaporation is less than half that done by condensate loading.
Highlights
The simulated cumulus fields are analyzed in the framework of an ensemble of entraining plumes by tracking a large number of Lagrangian parcels embedded in the large eddy simulations (LES) and grouping them into different plumes based on their detrainment heights
Among all cloudy updraft parcels that are from 612.5 m and detrain above 762.5 m, the 1% of the parcels that detrain at the highest levels are grouped together as one parcel group, the highest 1% and so on, totaling 100 parcel groups, with larger group numbers indicating higher detrainment heights
We have investigated how entrainment rates of shallow cumuli depend on environmental conditions and cloud characteristics by examining their responses to a small-amplitude temperature perturbation that is horizontally uniform and localized in height
Summary
The Harvard community has made this article openly available. Please share how this access benefits you. Journal of the Atmospheric Sciences 73 (2) (February): 839–854.
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