AN OBSERVATIONAL AND NUMERICAL STUDY OF A MINI-SUPERCELL STORM

The structure and evolution of a small, moderately intense supercell s torm, observed over northern Alabama on 17 July 1992, is described thr ough a combined observational analysis and numerical modeling study. W ind profiler measurements show that the storm formed within a favorabl e low-level wind shear regime confined only to northern Alabama over a limited time interval between conventional NWS rawinsonde times. Whil e not severe, this cloud system was long-lived and exhibited character istics similar to those of classic supercells, including a unicellular echo with multicellular substructures, an extended lifetime, a collar cloud and a flanking Line of cumulus. Moreover, this supercell did no t produce cloud-to-ground lightning over its lifetime, nor was thunder from intracloud lightning heard over a 20-min period as the storm mov ed by. Numerical simulations of the cloud system duplicate the general observational features, including horizontal and vertical dimensions, cyclic behavior and convective core and anvil characteristics. Simula ted distributions of microphysical fields indicate that a juxtapositio n of cloud ice, graupel and supercooled water did not occur in suffici ent concentrations to support effective charge separation by the non-i nductive charge mechanism, despite updraft magnitudes of 15-20 m s(-1) within the - 10 to - 20 degrees C levels of the cloud. (C) 1998 Elsev ier Science B.V. All rights reserved.