A Numerical Study of Traveling Microbursts

Abstract

An analysis of traveling microbursts in unidirectionally sheared environments is undertaken using a three-dimensional numerical model with 50-m resolution in a 19 ? 12 ? 4 km domain. For each run, the cooling source is centered at a height of 2 km and travels in an eastward direction of Cm, where Cm = 3, 6, 9, 12, and 15 m s?1. Environmental winds above 2 km are equal to Cm and decay linearly to 0 m s?1 below 2 km. The authors examine the kinetic energy budget of each run, focusing on the dynamic features that are not found in a static microburst simulation. As the source speed Cm increases from 0 to 9 m s?1, the magnitude of the surface horizontal winds increase in the direction of source movement. An examination of the dynamic pressure equation shows that rotationally induced pressure work forces are primarily responsible for increasing surface horizontal winds for the moving-source microbursts. In a similar form to previous studies of vertical perturbations in a sheared environment, elevated horizontal vorticity is generated by tilting of environmental vorticity and is strengthened by stretching imposed by the downdraft. The authors? results suggest that the magnitude of the damaging surface winds of a microburst can be enhanced significantly when the parent cloud is moving in a unidirectionally sheared environment.