Effects of Mid-Tropospheric Dry Air on Evolution of Supercell Storms

In order to investigate influences of mid-tropospheric dry air on supercell storm evolution, two idealized numerical experiments with different water vapor profiles (CNTL and DRY) are performed using the Advanced Regional Prediction System (ARPS). The initial condition in the CNTL is based on a Del City storm sounding, while the initial thermodynamic condition in the DRY case is modified by the addition of a mid-level dry layer to the CNTL sounding.

Both the experiments produce typical supercell storms. After t = 120 min., the storm in the DRY case is rapidly weakened, while the storm maintains the strength in the CNTL experiment. The budget analysis of the vertical momentum equation reveals that buoyancy within the main updraft region in the DRY is less than that of the CNTL. Trajectory analyses show that the less buoyancy in the DRY results from the inflow of low-potential buoyancy air into the updraft region near the surface as well as the subsequent entrainment of the ascending parcels. Results of additional experiments with various moisture profiles show that the suppression of supecellular convection is more effective when the dry layer is located at the lower level.