光学式ディスドロメータにより測定された桜島降灰粒子の解析

Abstract

In the present study, we analyzed the particle size distribution (PSD) of falling volcanic ash particles collected for a total of 205 eruptions in 2018-2020 at Sakurajima volcano in Kagoshima Prefecture, Japan. PSD data were measured with the DPRI optical disdrometer network. Assuming the gamma PSD model, we examined the relationships between each of the gamma PSD parameters calculated by the complete moment method. It was shown that there were good correlations between each of the gamma PSD parameters, which might be one of the characteristics of falling volcanic ash particles. We confirmed from the normalized gamma PSD analysis that the normalized intercept parameter and mass-weighted mean diameter are suitable for estimating the ash fall rate. The results of the present study provide essential information for studying microphysical processes in volcanic ash clouds and improving ash transport and sedimentation models. We also derived theoretical power law relationships between pairs of integrated PSD parameters, which can be applied to weather radar monitoring of ash fall distributions.