JpGU-AGU Joint Meeting 2017

Presentation information

[JJ] Oral

S (Solid Earth Sciences) » S-VC Volcanology

[S-VC49] [JJ] Mitigation of Volcanic disaster - Basic and applied research

Sun. May 21, 2017 1:45 PM - 3:15 PM A08 (Tokyo Bay Makuhari Hall)

convener:Mitsuhiro Yoshimoto(Mount Fuji Research Institute, Yamanashi Prefectural Government), Kazutaka Mannen(Hot Springs Research Institute of Kanagawa Prefecture), Shinji Takarada(Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology), Hisashi Sasaki(Asia Air Survey Co., Ltd.), Chairperson:Hisashi Sasaki(Asia Air Survey Co., Ltd.), Chairperson:Kazuto Saiki(Graduate School of Science, Osaka University)

1:45 PM - 2:00 PM

[SVC49-07] Physical parameters analysis of volcanic ash particles measured by 2D-Video Disdrometer

*Sung-Ho Suh1, Masayuki Maki2, Masato Iguchi3, Dong-In Lee1 (1.Division of Earth Environmental System Science, Pukyong National University, Korea, 2.Research and Education Center for Natural Hazards, Kagoshima University, Korimoto, Kagoshima, Japan, 3.Sakurajima Volcano Research Center, Disaster Prevention Research Institute, Kyoto University, Sakurajima, Kagoshima, Japan)

Keywords:Volcanic ash, basic feature, 2DVD

Weather radar is one of powerful instruments for measuring volcanic ash columns and ash clouds. However, we need fundamental physical properties on ash particles for the quantitative analysis of weather radar data of volcanic ash: necessary information are terminal velocity, axis ratio, and canting angle including density and dielectric constant of target to detect volcanic ash column correctly. In the present study, the basic features of volcanic ash particles are analyzed to develop quantitative ash fall estimations (QAEs).
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.