Hydrostatic Equilibrium Questions and Answers

Answer: A

Entrainment brings environmental air into the updraught, diluting its buoyancy and its moisture, while detrainment expels cloudy air outward near the top. The two together determine the vertical profile of mass flux in a convective plume. Getting the entrainment rate right is one of the central difficulties of convective parameterisation and a persistent source of model error.

Answer: B

Entraining drier cooler air reduces the buoyancy, so a strongly entraining plume loses its buoyancy at a lower level and produces a shallower cloud. Narrow plumes entrain proportionally more than wide ones, which is why small cumulus remain shallow while large ones grow deep. Schemes commonly make the entrainment rate inversely proportional to the plume radius for exactly this reason.