11:30 AM - 11:45 AM
[AAS04-04] Entrainment rate of convective thermal
Keywords:Entrainment rate, Large eddy simulation, Cumulus convection, Convective thermal
Entrainment is a key process influencing the characteristics of convection. Recent studies have shown that deep convection consists of thermals—discrete, buoyant spherical structures that ascend through the atmosphere. In this study, we evaluated the entrainment rate of convective thermals.
We conducted an idealized simulation of deep convection, representing the diurnal cycle over tropical land, with a grid spacing of 125 m. This simulation successfully reproduced deep convection, including its turbulent structures. The entrainment rate was estimated using a passive scalar advected by the local wind. The scalar’s environmental concentration decreases with height, and as a thermal ascends, its scalar concentration decreases due to entrainment of the surrounding air.
On average, the entrainment rate decreases as the thermal size increases. However, the entrainment rate varies significantly among thermals of similar size, suggesting that entrainment is a stochastic process. We also investigated how the entrainment rate depends on environmental wind. For isolated convection, vertical wind shear has little effect on the entrainment rate.
We estimated the buoyancy of thermals using a simple parcel model that accounts for entrainment. When applying the entrainment rate specific to each thermal, the model accurately predicts its buoyancy. However, when using the average entrainment rate, the model fails to predict the buoyancy of individual thermals.
We conducted an idealized simulation of deep convection, representing the diurnal cycle over tropical land, with a grid spacing of 125 m. This simulation successfully reproduced deep convection, including its turbulent structures. The entrainment rate was estimated using a passive scalar advected by the local wind. The scalar’s environmental concentration decreases with height, and as a thermal ascends, its scalar concentration decreases due to entrainment of the surrounding air.
On average, the entrainment rate decreases as the thermal size increases. However, the entrainment rate varies significantly among thermals of similar size, suggesting that entrainment is a stochastic process. We also investigated how the entrainment rate depends on environmental wind. For isolated convection, vertical wind shear has little effect on the entrainment rate.
We estimated the buoyancy of thermals using a simple parcel model that accounts for entrainment. When applying the entrainment rate specific to each thermal, the model accurately predicts its buoyancy. However, when using the average entrainment rate, the model fails to predict the buoyancy of individual thermals.