IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

1A2_4F-O5Room A6

Date/Time: July 21 11:45-12:00

Polarimetric radar observations of volcanic eruptions
Masayuki MAKI1 , Takeshi MAESAKA2 , Tomofumi KOZONO3
1Kagoshima University, Japan, 2 NIED, Japan, 3 NIED, Japan
E-mail: maki3@dia-net.ne.jp

There have been several reports of ’conventional’ radar succeeded in detecting volcanic eruptions and estimating
ash amount distributions. In addition to this information, ’polarimetric’ radar has the potential to deduce themicrophysical properties of volcanic ash particles such as ash particle size distribution, particle shape and postural.
From analogy of past studies of hydrometeor classification in radar meteorology, polarimetric radar parameters
may be used to discriminate ash particles from hydrometeors, which is a difficult task for non-polarimetric radar.
The present study examines the potential use of polarimetric weather radar in the detection of volcanic eruptions,quantitative ash fall estimations (QAE), and the microphysical retrieval of ash particles.
The radar data analyzed in the present study are from the eruptions of the Mt. Shinmoedake volcano (1,421 mASL) in the Kirishima Mountan Range and the Mt. Minamidake volcano (1,040 m ASL) in Sakura-jima, Kagoshima
prefecture, both of which are located in southern Kyushu, Japan. The data selected for analysis are based on
the Japan Meteorological Agency (JMA) monthly report on volcano activity, collected from 27 explosive eruptionsof the Mt Shinmoedake volcano during the period January to March 2011, and 12 explosive eruptions of the Mt.
Minamidake volcano during the period July to October 2012. The radar data from the Mt. Shinmoedake eruptions
were collected by Kunimiyama C-band polarimetric radar, which was located 67.8 km south of the Mt. Shinmoedake
volcano. The radar data from the Mt. Minamidake eruptions were collected by Tarumizu X-band polarimetric radar,which was located approximately 11 km south-southeast of the volcano.
Based on analysis of the eruption time period, the maximum and accumulated reflectivity factor, and the differentialreflectivity of the volcanic ash, we reach the following conclusions:1) Operational polarimetric weather radar has the potential ability to quantitatively estimate the amount of volcanicash expelled during volcanic eruptions.
2) The Z-A relationship, where Z is reflectivity and A is the ash amount, can be derived if ground measurements of
the ash amounts are available.
3) The coefficient and exponent of the power low function of the Z-A relationship is dependent on each volcanic
eruption, which may be due to the difference in ash particle size distribution.
4) Differential reflectivity over a volcano crater fluctuates in space and time, while showing significant spatiotemporal
patterning in the downwind regions, which suggests the presence of an ash particle aggregation and sorting
mechanism.
5) The radar cannot detect weak ash echoes due to the minimum detectable reflectivity, which depends on therange from the radar and the receiver noise level of the radar system.
6) In-situ measurements of ash particles are necessary for more detailed analyses of polarimetric radar
parameters.

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