Identification of preferred areas of shower development by means of high power radar

Abstract

AbstractA high‐power, high‐gain radar has been used to investigate clear air echoes on days when surface heating produced low‐level convection. The echoes were from irregular refractive index gradients produced primarily by gradients of water vapour density of small scale (5 cm). It was observed that the height to which the convection extended was revealed by an almost continuous layer of echo. This layer was perturbed on a scale of kilometres by individual convective elements; in addition Areas of Deeper Convection (termed ADCs) some tens of kilometres across occurred. These features are described in this paper. Individual ADCs were identifiable as entities for several hours, and, on the one occasion when reliable movements could be determined, they travelled with the low‐level wind. When the vertical structure of the atmosphere was such that showers occurred, they developed only within ADCs. Evidently the showers occurred in clusters because of the pre‐existing structure of the convective layer and not because individual showers modified their near environment.On two of the four occasions studied the ADCs could be related directly to topographical features. In one case of negligible wind an ADC developed and remained close to hills; on another occasion a plume‐like area of deeper convection over 100 km long appeared to stream away from high ground. More generally, however, advection of ADCs masked possible topographical influences.It is suggested that by using a high power radar to identify ADCs it may be possible to forecast the location of outbreaks of showers and thunderstorms more precisely than is possible at present. Further lines of research are also proposed.