Inhibition of Downdrafts by Stable Layers in Tropical Deep Convection

According to the ventilation theory of Tang and Emanuel, one method by which midlevel dry air can inhibit tropical cyclone (TC) intensification is by enhancing downdrafts that inject low-entropy air into the boundary layer. In a mature TC, this low entropy air is then drawn into and weakens the eyewall convection (and, thus, the TC secondary circulation) via a reduction in buoyancy. Idealized simulations of tropical deep convection suggest the possibility that a stable layer can impede the downward progress of downdraft air in tropical deep convection, preventing the injection of low-entropy air into the boundary layer. Based on ventilation theory, it is plausible that either preventing or delaying the injection of the low-entropy air into the TC inflow layer could weaken the influence of midlevel dry air on TC intensity.

This presentation will examine the motivating idealized simulations and explore the potential implications that the downdraft/stable-layer interaction, where the stable layer impedes the downward progress of the downdraft air, might have on the convective evolution of TCs and tropical disturbances. Furthermore, the presentation will also include preliminary results of ongoing work to determine the sensitivity of the downdraft/stable-layer interaction to the strength of the stable layer and downdraft. Additional work is also underway to detect these downdraft/stable-layer interactions in observations.