The atmospheric overturning induced by Hector the Convector

The overturning of Hector the Convector, a tropical multicellular convective system of northern Australia that regularly overshoots into the stratosphere, is synthesized at the scale of a large-eddy simulation. The isentropic analysis offers the advantage of filtering out the reversible motions due to gravity waves and taking into account the turbulent fluxes that contribute to the vertical transport. Two key circulations are characterized: the troposphere deep overturning and the mass exchange due to the overshoots into the stratosphere. The transition from deep to very deep convection is associated with a change in the diabatic tendency inside the tallest updrafts: the latent heat release due to the formation of a large amount of icy hydrometeors exceeds the loss of energy due to mixing with the drier, colder air of the environment. In agreement with a previous study of Hector examining the properties of its two tallest updrafts, the entrainment rate exhibits a minimum during the very deep convection phase as low as 0.04 km^-1. The overturning intensity corroborates the Eulerian computation of the vertical mass flux in the midtroposphere and in the lower stratosphere. It however gives a lower estimate of the flux in the upper troposphere, filtering out the reversible motions, and a larger estimate in the lower troposphere and at the tropopause, where slow vertical motions contribute significantly to the transport.