Simulation and analysis of tornado development and decay within a three-dimensional supercell thunderstorm

Abstract

A three-dimensional numerical simulation using a two-way interactive nested grid is used to study tornado-genesis within a supercell. During a 40-minute period, two tornadoes grow and decay within the storm's mesocyclone. The tornadoes have life spans of approximately 210 minutes. Maximum ground-relative surface wind speeds exceed 60 m s-1 during both tornadoes, and horizontal pressure gradients reach 18 hPa km-1 during the second tornado. Comparison of the simulated storm evolution with Doppler and field observations of supercells and tornadoes shows many similar features. Vertical vorticity in the mesocyclone and the tornado vortex at low levels is initially created by the tilting of the environmental vorticity and baroclinically generated vorticity along the forward flank gust front of the storm. Tornadogenesis is initiated when mesocyclone rotation increases above cloud base. -from Authors