Physical and numerical modelling of thunderstorm downbursts

In this study, a static continuous impinging jet has been used to simulate a thunderstorm downburst. Velocity characteristics have been investigated at various positions in the Bow over flat terrain, and over simple topographic features, thereby yielding topographical speed-up factors. A generic empirical equation describing the development of the velocity profile over a hat board has been developed. Comparison with previous works with impinging jets and conventional boundary layer flow speed-up factors has been completed. Speed-up factors were similar at the crest of the embankment, but dropped off rapidly behind the crest compared with boundary layer flow. Preliminary studies using computational fluid dynamics to predict the flow regime over topographical features has been shown to give reasonable agreement. (C) 2001 Elsevier Science Ltd. All rights reserved.