Structure and life cycle of microburst outflows observed in Colorado.

Abstract

Discusses the structure of microbursts, intense small scale divergent outflows, from data obtained in Colorado, and considers similarities between microbursts and wall jets. Outlines procedures and equipment used in the JAWS project, and notes how the wind fields were derived from the radar data. Analysis reveals that microbursts can be categorized into individual events and microburst lines. Features of microburst outflows are horizontal vortices and dust rings. Presents photographs and radar observations, plus a table of observed characteristics. profiles of radial velocity indicate that, within the impaction zone, the wall jet profile is a reasonable approximation, but that beyond the velocity maximum the microburst profiles decay more rapidly. Examines the structure of embedded microbursts, those in strongly directional flow, and discusses symmetry considerations. Most microburst lines were produced by lines of virga or lines of thunderstorms, including squall lines. Outflow depth and length are greater than for individual events. Implications for aircraft safety, notably the "rotors" and asymmetry (minimum shear 60% of the maximum) are discussed.