Abstract
It is well known that rainfall rate is enhanced over mountains due to orographic uplifting. It would be beneficial to rainfall nowcasting if the intensity of the orographic enhancement could be estimated using simple parameters. In the present study, we found a clear relationship between orographic enhancement of the rainfall rate and the movement speed of radar echoes in a case study of rainfall over mountains in the southwestern area of the Kanto District in Japan during Typhoon 0709, by using rainfall data derived from X-band polarimetric radar. The increasing rate of rainfall rate per unit altitude (ΔR/ΔH) showed a positive correlation (r = 0:95) with the movement speed of radar echoes (V) when V > 10 m s-1. Such a correlation suggests that V is an effective parameter for quickly estimating the orographic enhancement of rainfall, however, more case studies are required before it can be used in practical applications.
