Entrainment in Tropical Deep Convection

 

Authors

Usama Anber — Brookhaven National Laboratory
Scott Giangrande — Brookhaven National Laboratory
Michael Jensen — Brookhaven National Laboratory

Category

Convective clouds, including aerosol interactions

Description

Entrainment is one of the key processes influencing deep convection and its characteristics, such as the vertical velocity, buoyancy, and cloud height. Nonetheless, its representation in numerical weather and climate models remains a major challenge. Recent body of work has established a robust relationship between entrainment and the updraft vertical velocity in convective cores, nominating the vertical velocity as a successful candidate to be incorporated in coarser numerical models to represent entrainment. In this study, cloud-resolving simulations were performed to simulate deep convective events in the tropics over a wide range of large-scale tropical conditions. Simulated cases include convective events from GoAmazon, TWP-ICE, AMIE-GAN/Dynamo, and idealized radiative-convective equilibrium (RCE). Entrainment is directly computed using the mass conservation of cloudy air encompassed by the cloud material surface in which entrainment is defined as a mass sink. Then a linear relationship is established between entrainment rate and the in-cloud updraft vertical velocity. It is found that the slope (and the vertical structure of entrainment rate) defining the relationship is different between different tropical regions. This suggests that the mixing time scale of the environmental air with clouds is dependent on factors controlling the large-scale environment. Such factors include large-scale vertical mass flux and the vertical wind shear of the horizontal winds typically found during the active phase of the MJO (Dynamo).