Abstract
Atmospheric radio-refracti v e index is determined by the well-known formula based on DEBYE'S idea. This formula is used unaltered even in rainfall. However, judged from the fact that the electromagnetic scattering effect of waterdrops in rainfalls can be usually detected as radar-echoes, the existence of waterdrops must influence the radio-refractive index in the atmosphere. This problem is approached and discussed assuming Rayleigh scattering for a single drop and approximate mutual reactions among the scattered waves. It is concluded from the result obtained using the data on hydrometeors, that the influence upon the refractive index or the equivalent radiorefractive index could hardly be disregarded in certain cases.
