9:00 AM - 9:15 AM
[MIS13-01] Radar Meteorological Study on Falling Volcaic Ash Particles
★Invited Papers
Keywords:particle size distribution, disdrometer, polarimetric radar parameters
In the present study, we describe fundamental characteristics of falling volcanic ash particles such as the particle size distribution, fall velocity, shape, et al. from the radar meteorological view point. Because it is beneficial for the weather radar monitoring of ash fall to identify similarities and differences between rain drops and ash particles, we present the results of analyses of the rain drop data collected by two-dimensional video disdrometers, As for the volcanic ash particles, we presented the results of Maki et al. (2021) who analyzed the particle size distribution (PSD) of falling volcanic ash particles measured using optical disdrometers during six explosive eruptions of the Sakurajima volcano in Kagoshima Prefecture, Japan. We found that PSD for both rain drops and ash particles could be expressed by the gamma distribution, N(D) = N0Dμ exp(–ΛD), where N(D) is the particle size distribution, D is the particle diameter, N0 is the intercept parameter, Λ is the slope parameter, and μ is the shape parameter. The relationships between each of the gamma PSD parameters were shown to be a characteristic of falling volcanic ash particles. The strong correlation between RA/Nw and Dm suggests that the normalized intercept parameter Nw and mass-weighted mean diameter Dm are suitable for estimating the ash fall rate RA. We also derived empirical power law relationships between pairs of integrated PSD parameters: RA, the volcanic ash mass concentration CA, the reflectivity factor Z, and the total number of the ash particles per unit volume NT. The results of the present study provide essential information for studying microphysical processes in volcanic ash clouds, for developing a method for quantitative ash fall estimation using weather radar, and for improving ash transport and sedimentation models.