Numerical simulations of an isolated microburst. Part I: dynamics and structure

Abstract

A microburst downdraft is initiated by specifying a distribution of precipitation at the top boundary of the model and allowing it to fall into the domain. The simulated microbursts were driven primarily by evaporative cooling of rain and, second, by cooling due to the melting of hail. Net warming within the upper regions of the precipitation shaft maintained the downdraft top near the melting level. The greatest temperature departures from ambient were at the ground. Mean horizontal wind shear was negligible 4 min prior to the time of maximum outflow winds, but reached an overall peak 2 min later. The numerical simulations produced a microburst ring vortex, cool low-level outflow with a burst-front head and nose structure, and a pressure nose beneath the microburst downdraft. The ring vortex propagated downward with the descending precipitation shaft and rapidly intensified prior to reaching the ground. -from Author