The Life Cycle of a Thunderstorm in Three Dimensions

Abstract

The results of an isolated three-dimensional thunderstorm simulation are reported. An initial wind shear of 1.54 m sec⁻¹ km⁻¹ is specified in the x direction and symmetry is assumed in the y direction about the central x-z plane. An erect cloud develops from an initial 3.7 km radius impulse as the updraft core is fed from all directions by moist and warm low-level air. After some time rain begins to fall and a downdraft developes downshear of the updraft core cutting off the major low-level supply of warm and moist air. Subsequently, the updraft core begins to tilt downshear and the center of the lower part of the updraft core is shifted away from the central x–z plane. At middle cloud levels wind features reminiscent of flow about a cylinder are present. Both the hydrostatic and dynamic pressure appear to be important in decelerating flow upwind of the cloud. Comparison with a similar two-dimensional simulation indicates that the three-dimensional cloud develops faster, grows taller, lasts longer, and travels farther and faster. This is indicative of differences in geometry which in turn are related to low-level moisture supply for cloud growth and to subsidence in the cloud environment.