A study of microphysical processes in the 2 August 1981 CCOPE supercell storm

Abstract

A three-dimensional, time-dependent, non-hydrostatic model is used to simulate the microphysical processes in an intense supercell storm that passed through the Cooperative Convective Precipitation Experiment (CCOPE) network on 2 August 1981. The simulation utilizes the hail parameterization model (HPM) version of the Wisconsin Dynamical/Microphysical Model (WISCDYMM), in which the precipitation fields are all assumed to follow exponential size distributions, while cloud water and ice are assumed to be monodispersed. The simulation is carried out for 7200 s and is found to exhibit dynamic and thermodynamic features characteristic of the observed storm, including an intense and persistent updraft with strong rotation in the lower and mid levels, an undiluted updraft core, and a cool pool and gust front which propagates along with the storm beneath the subcloud region. A supercellular structure is also depicted in the microphysical fields by a large overshooting top, large forward overhanging anvil, low-level hook-like feature and distinct bounded weak-echo region. Calculations of the total integrated hydrometeor mass for the entire domain show that more than 80% of the storm hydrometeor mass is ice, with graupel and hail being the most predominant type. The total mass of ice, snow, graupel and hail increase rapidly with storm intensity, while the total liquid water mass consisting of cloud water and rain increase much more slowly as shown by time-dependent distributions of the hydrometeor types. Production and depletion curves depicting microphysical processes for each precipitating hydrometeor indicate that rain is produced primarily from the melting and shedding of graupel and hail, snow is primarily initiated by the Bergeron-Findeisen process and grows predominately from the accretion of cloud ice and cloud water, and graupel and hail is primarily initiated through rain-snow collisions and has largest mass gains through accretions of cloud water, rain and snow. The largest sinks are evaporation and accretion by graupel and hail for rain water, sublimation and accretion by graupel and hail for snow, and melting and shedding to form raindrops for graupel and hail.