Microphysical and Dynamical Characteristics of Low-Precipitation and Classic Supercells

Abstract

he sensitivity of supercell morphology to the vertical distribution of moisture is investigated in this study using a cloud-resolving model with 300-m horizontal grid spacing. Simulated storms are found to transition from classic (CL) to low-precipitation (LP) supercells when the strength of elevated dry layers in the environmental moisture profile is increased. Resulting differences in the microphysical and dynamical characteristics of the CL and LPs are analyzed.The LPs produce approximately half of the accumulated surface precipitation as the CL supercell. The precipitating area in the LPs is spatially smaller and overall less intense, especially in the rear-flank downdraft region. The LPs have smaller deviant rightward storm motion compared to the CL supercell, and updrafts are narrower and more tilted, in agreement with observations. Lower relative humidities within the dry layers enhance evaporation and erode the upshear cloud edge in the LPs. This combination favors a downshear distribution of hydrometeors. As a result, hail grows preferentially along the northeastern side of the updraft in the LPs as hail embryos are advected cyclonically around the mesocyclone, whereas the primary midlevel hail growth mechanism in the CL supercell follows the classic Browning and Foote model. The differing dominant hail growth mechanisms can explain the variations in surface precipitation distribution between CLs and LPs. While large changes in the microphysical structure are seen, similarities in the structure and strength of the updraft and vorticity indicate that LP and CL supercells are not dynamically distinct storm types.