How does mid-tropospheric dry air affect the evolution of supercellular convection?

• The effect of midlevel dry air on supercellular convection is examined.
• Dry air aloft suppresses the development of supercells via two processes.
• One is entrainment and the other is the dry-air penetration process.

To investigate the influence of mid-tropospheric dry air on the evolution of supercell storms, idealized numerical experiments with several moisture profiles were performed. In an environment with (without) a mid-level dry layer, supercellular convection decays immediately (persists for a long period). A set of trajectory analyses revealed that two suppression processes contribute to the convection decay in the environment with the mid-tropospheric dry layer. One is the entrainment process within the mid-tropospheric dry layer, and the other is the dry-air penetration process. In the latter process, dry air penetrates into the low-level updraft region, so that the supply of warm, moist air for convection is reduced. Neither of the processes contributes effectively in an environment with a dry layer located at a higher altitude. The dependence of the results on the environmental shear profile, evaporation rate, and the amount of convective available potential energy (CAPE) was also examined by additional experiments.