Relation between Measured Radar Reflectivity and Surface Rainfall

TLDR

The relationship between radar reflectivity and surface rainfall is affected by factors such as raindrop‑size distribution variations, hail or melting snow enhancement, downdraft attenuation, and low‑level rainfall changes due to accretion or evaporation. The study examines these factors theoretically and through detailed radar–raingauge comparisons. In 374 radar–raingauge comparisons across twenty storms, the study quantified the magnitude of each factor, identified storm types where they are significant, and proposed compensation approaches.

Abstract

A number of physical factors that influence the relation between measured radar reflectivity and surface rainfall are considered both theoretically and through detailed comparisons of radar and raingauge measurements. These factors include natural differences in raindrop-size distributions, enhancement of radar reflectivity by presence of hailstones or melting snow, diminution of reflectivity by downdrafts, and low-level changes in rainfall rate caused by accretion or evaporation. Results of 374 comparisons in twenty storms, which cover a wide variety of synoptic situations and rainfall patterns, are presented. Magnitudes of the effects of the different factors are estimated, and storm types where they are likely to be significant are pointed out. Also, some ways of compensating for the observed effects are suggested.