1:45 PM - 2:00 PM
[SVC49-07] Physical parameters analysis of volcanic ash particles measured by 2D-Video Disdrometer
Keywords:Volcanic ash, basic feature, 2DVD
The data were collected by a number of automatic tephrometers at Sakurajima volcano, Japan and reanalyzed with a 2D-video disdrometer (2DVD) in the large-scale rainfall simulator of NIED. The entire volcanic ash particles were classified as five types based on shape and orientation: Horizontal Oblate (OH), Vertical Oblate (OV), Horizontal Prolate (PH), Vertical Prolate (PV), and Sphere (Sp).
Dominant particle shape was OH (71.5%) and the next was PH (17.0%). It should be noted the horizontally oriented type was 88.7% of all sampled data. The 64.4% data are concentrated on D < 0.5 mm. The number of PV and Sp particle is increased with D. The relationships of terminal velocity are dependent on particle shape types: Prolate spheroid (vertical orientation) particles were faster than those of oblate (horizontal). The distribution of γ is from 0 to 1.5 at D < 2 mm, but these are concentrated to around 1 for D > 2 mm. The deviation of canting angle for OV (OH) is around two times larger (smaller) than raindrops. It is inferred that there would be not much rotating phenomenon.
The features of ZH and dual-pol radar variables (ZDR, KDP, and AH) were analyzed. ZH is around 4.3 dBZ smaller than that of raindrop and there is no resonance effects with radar frequency. There are large variabilities in ZDR depending on the particles shape for D < 2mm and these were close to 0 for D > 2mm. KDP and AH are variable with radar frequency but these magnitudes are almost 0 regardless of D.
These results will be utilized to develop QAE methods, to detect volcanic ash column and predict its activity.
Corresponding author: M. Maki
Acknowledgment: This work was supported the Grant-in Aid for Scientific Research (A) 24244069 of MEXT, Japan, Invitation Program of Foreign Researchers of Kyoto University and the Korea Meteorological Industry Promotion Agency under Grant KMIPA 2015-1050 and the BK21 plus Project of the Graduate School of Earth Environmental Hazard System. 2DVD data were provided by MEXT, Japan. We also thanks to NIED for the experiments in the large-rainfall simulator in Tsukuba, Japan.