The Dynamics of the Convective Process in Clear Air as Seen by Radar

Abstract

Sensitive, high-powered radar have been used to study the dynamics of the convective process in optically clear air. Various stages in the development of the convective field have been identified on the basis of distinctive radar patterns of the cells. The characteristics of the convective field as a whole and the individual cells making up the field during each stage are discussed. During the initial formation stage, the radar returns are diffuse and mottled. Following the destruction of the surface inversion, the first doughnut or ring-shaped radar returns appear which mark the beginning of the field growth stage. At the onset of this stage, the cells are small, around 100-200 m in diameter. As time progresses, the height of the convective field increase at a rate of 4.5-6 m min? 1, while the convective cells themselves grow to several thousand meters in diameter. Based on a comparison of the radar patterns with previous aircraft measurements of the physical properties of convective cells, it is suggested that the strong, patterned radar returns from the top of the convective field are from individual cells which are cold and moist relative to a slightly stable environment.