Volcanic ash size distribution determined by weather radar

A Doppler weather radar has been observing routinely the backscatter from ash emitted by a volcano on top of Mt. Oyama on Miyake Island-south east of Tokyo. The purpose of this paper is to show that the time dependent size distribution N(D,t) of ash particles can be obtained from the time dependence of the reflectivity factor Z(t) in the radar's resolution volume V/sub 6/ ( Doviak and Zrnic 1993) advecting with the wind. It is assumed that Z(t) is controlled by the different times required for ash particles of different diameters D and terminal velocities to empty V/sub 6/.