TEMPORAL VARIATIONS IN THE SCALING PROPERTIES OF RAIN ECHOES DURING THE DEVELOPMENT OF A COLD LOW IN SASKATCHEWAN

A better understanding of the scaling properties of rain could assist in parameterizing rain events in hydrological models and support the d evelopment of improved ''weather generators.'' A technique developed f or the analysis of the scaling characteristics of snow patches during melt has been adapted to study the development of rain echoes observed by radar. The technique is applied to echo ensembles detected by a we ather radar located at Elbow, Saskatchewan, for a 48-h period from 180 0 LST 30 June to 1800 LST 2 July 1991. The scaling properties and othe r statistical measures of ensembles of radar echoes from 2-km MSL CAPP I (constant-altitude plan position indicator) maps were analyzed for a 240 km x 240 km square domain centered on Elbow. The 0.2 mm h(-1) rai n rate was used to define the echoes. During the 48-h period, the size s, numbers, and shapes of echoes within the domain changed considerabl y as a result of a cold low that intensified just outside the study ar ea and then moved eastward. Analyses of some scaling properties of the se ensembles were carried out along with tests of their sensitivity to reflectivity threshold. The echo ensembles were characterized by the perimeter/area and Korcak parameters. The perimeter/area parameter pro vides a measure of the ''roughness'' of the edges of the echoes. Value s of the perimeter/area parameter from this study agreed well with the results obtained by other investigators who used different data sourc es and techniques. The Korcak parameter, which represents the ''clumpi ness'' of the pattern, was more variable. Changes in this parameter ma y serve as a precursor to significant changes in the overall rain patt ern. Both the statistical properties and the scaling properties of ech o ensembles were found to vary depending on the effects of the dynamic and thermodynamic atmospheric controls on rain formation.