Journal of Natural Disaster Science, Volume 37，Number 2，2016，pp79-90

Numerical Simulation of Volcanic Ash Plume Dispersal from Kuchinoerabujima
on 29 May 2015
Hiroshi L. TANAKA1 and Masato IGUCHI2
1: Center for Computational Sciences, University of Tsukuba
Tsukuba 305-8577 JAPAN
2: Sakurajima Volcano Research Center
Disaster Prevention Research Institute, Kyoto University
Kagoshima 891-1419 JAPAN（Received:Sep 9, 2016 Accepted:Nov.2, 2016）

Abstruct
In this study, airborne ash dispersal from the eruption of Kuchinoerabujima Volcano in Japan on 29
May 2015 is simulated using the volcanic ash tracking PUFF model. A major eruption occurred at 9:59 am
local time (0:59 UTC), and the ash plume reached 9 km above the ground. According to MTSAT-2 satellite
monitoring, the ash plume with a mushroom-shaped distribution drifted in the east-southeast direction. The
observed ash fallout over Yakushima Island is in the order of 100 g/m2. Using this observational fact, weestimated that a particle in the numerical model represents 60 tons of ash mass. Based on this number, total
emissions are estimated to be 600,000 tons for this event. The result suggests that the ash concentration in
the air can also be estimated by this method. According to the aviation safety report, an ash density of 4
mg/m3 and above is considered as a danger zone for commercial airliners. The PUFF model simulationshows that the core region of the plume front at 9 km in height indicates 100 mg/m3 of airborne ash density
even for the plume 250 km from the erupting volcano. The satellite images show the exact location of theash plume. The PUFF model simulation can therefore estimate the airborne ash density over a much wider
diffused area to identify the danger zone for aircraft.
Keyword: PUFF model, Kuchinoerabujima Volcano, aviation safety, airborne ash density, ash dispersion

1.

Introduction

A major volcanic eruption occurred on Kuchinoerabujima (657 m) at 9:59 am local time (0:59 UTC) on 29
May 2015. Kuchinoerabujima Volcano is an active volcanoe of the Ryukyu Island arc, Japan. The island islocated at 30.44°N / 130.22°E, which is about 100 km south of the southern tip of Kagoshima Prefecture
in Japan. A tall mushroom ash plume reached 9 km above sea level within 10 min. The initial radius of thecircular anvil cloud was about 10 km for the first 20 min. The phreatomagmatic eruption from the vent ofMount Shindake, the island's main peak, generated a pyroclastic flow that reached the shoreline of the island.
The Japan Meteorological Agency (JMA) raised its volcano alert to the highest level of 5 at 10:07 am (01:07
UTC). Fortunately, there were no reports of injuries or damage owing to the immediate evacuation.
Kuchinoerabujima Volcano then erupted on 18 and 19 June, but no eruption has been observed since 19
June 2015. (JMA Website for Ash Fallout Prediction, 2015: http://www.jma.go.jp/jp/ashfall/).
According to the high resolution MTSAT-2 satellite imagery at 2:10 UTC (see Fig. 1), the ash cloudappeard over Yakushima Island in a dark color while ordinary clouds appeared in white by the newly
installed color imagery of MTSAT-2.

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Fig. 1 MTSAT-2 (Himawari-8) satellite imagery of the volcanic ash plume from Kuchinoerabujima erupted
at 0:59 UTC on 29 May 2015. Dark ash cloud is seen over Yakushima Island at 2:10 UTC (animation
provided by JMA Web: http://www.jma-net.go.jp/sat/data/web89/himawari8-sample-data.html).
We can clearly identify the ash cloud by viewing a high-speed animation of the cloud movement. The
movement of the volcanic ash plume is traced in Fig. 2 using the MTSAT-2 satellite data. The plume top of
9 km in height soon spread in an east-west direction from the volcano. The elongated shape of the plume
top started to drift toward Yakushima Island. By 11:00 am local time (2:00 UTC), the ash front had reached
Yakushima Island located 20 km east of Kuchinoerabujima. The front edge of the ash plume over
Yakushima Island was elongated in the north-south direction while the tail of the ash plume was connectedto the vent of the volcano. At 11:40 am (2:40 UTC) the front edge of the ash plume had passed YakushimaIsland, and clear mushroom head distribution appeared for the ash plume in the north-south direction on
the satellite image. There was a tail from the ash plume head connected to the erupting volcano. The lower
part of the ash plume drifted westward while the upper part of the ash plume moved in the east-southeast
direction.

Fig. 2 Distribution of volcanic ash plumes from Kuchinoerabujima (black circle), traced from the satellite
images for 2:00 (blue), 2:40 (yellow), and 3:40 (red) UTC.
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The wind direction at the boundary layer was opposite to that of the upper level, as confirmed by
the movement of ordinary clouds in different vertical levels. At 12:40 pm (3:40 UTC), the mushroom head
distribution of the ash plume expanded further in the north-south direction, reaching Tanegashima Island,
and the tail of the ash plume was connected to the volcano. The lower part of the ash drifted further
westward due to the strongly sheared air flows near the volcano. By 3 hours after the eruption, the frontedge of the ash plume top drifted east-southeast over the North Pacific at 100 km from the volcano.
Ash plumes that flow and travel in the air, especially those of the Plinian type, are danger to aviation
safety even for the aircraft that are far from an erupting volcano. The first well known report of a serious
encounter with an airborne ash plume was that concerning the incident of a KLM jumbo jet approaching
Anchorage International Airport from Europe in December 1989. At that time, the aircraft was flying over
Mt. McKinley, and Redoubt Volcano was erupting and ejecting a large amount of ash into the upper
troposphere and travelled 300 km from Redoubt Volcano. All four engines stopped due to the dense ashthat melted and jammed the engines. The aircraft stalled lost power and dropped to 10,000 feet above theground (Hobbs et al., 1991; Casadevall, 1994). Fortunately, one of the engines recovered due to the coolingand removal of the jammed ash from the engines. After this incident, the International Civil Aviation
Organization (ICAO) established Volcanic Ash Advisory Centers (VAAC) at 9 sectors in the world,
including the Tokyo VAAC established in 1997 (see Onodera 1997). However, similar incidents ofcommercial airliners encountering volcanic ash have occurred many times since then.
In order to avoid volcanic hazards, especially for aviation safety purposes, a number of ash plumedispersion models have been developed under the VAAC activities. For volcanic hazard and aviation safety,
refer to the comprehensive review by Onodera (2013). Among those dispersion models, Tanaka (1994)
developed a real-time volcanic ash plume tracking model, called the PUFF model, at the GeophysicalInstitute, University of Alaska Fairbanks. The PUFF model here is a Lagrangian model tracking ash
particles, and is different from the conventional puff-plume model of air pollution study. The PUFF model
was applied to volcanoes in the northeastern Pacific Rim by Searcy et al. (1998), and has been operational
under Alaska Volcano Observatory since the eruption of Redoubt Volcano in 1990 (Tanaka, 1991; Kienle
et al., 1991; Dean et al., 1993). The PUFF model was transplanted to the US Geological Survey, US National
Weather Service, Japan Airlines, Japan Weather Association, and University of Tsukuba, Japan. The
performance of the volcanic ash tracking PUFF model has been examined for Alaskan volcanoes (Tanaka
et al., 1993; Akasofu and Tanaka, 1993), for Usu Volcano (Tanaka and Yamamoto, 2002), and for many
actual eruptions occurring throughout the world, including Kelud Volcano in Indonesia (Tanaka et al. 2016).
By comparing the ash fallout using the PUFF model with the dense observation network around
Sakurajima, the discharge rate of the ash mass from the crater was estimated by empirical formulae using
seismic monitoring and ground deformation data (Iguchi, 2012; 2016). The combination of the real-time
PUFF model simulation with the real-time seismicity, tilt and strain monitoring enables us to establish aquantitative evaluation of the airborne ash density as well as the distribution of ash fallout on the ground.
The PUFF prediction system is now applicable to any volcano. According to the assessment of aviation
safety by ICAO, an ash density of 4 mg/m3 and above is considered a the danger zone for commercial
airliners (Kelleher 2010). Estimation of the airborne ash density by the PUFF model offers useful
information for aviation safety.
The purpose of this study is to simulate the volcanic ash plume dispersal from Kuchinoerabujima
Volcano, which erupted on 29 May 2015, using the PUFF model. In this study, the 3D distributions andtime variations of airborne ashes are simulated quantitatively, based on the ground observation of ash fallout
at Yakushima Island.
The PUFF model simulation is expected to identify the location and spread of the danger zone for aviation
control in a major eruption of Kuchinoerabujima Volcano in Japan.

2.

Description of the PUFF model

The PUFF model for a real-time volcanic plume prediction was constructed by Tanaka (1991; 1994) and81

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reported in detail by Searcy et al. (1998) and by Tanaka et al. (2016). The model is based on the threedimensional (3D) Lagrangian form of the fluid mechanics. We assume a vertical column of initial ash
particles that are transported and diffused by winds and turbulence in a 3D space. In the Lagrangianframework, material transport is conducted by the fluid motion, and diffusion is represented by a stochastic
process of random walk (e.g., Chatfield, 1984). Here, the plume dispersion model is constructed by asufficiently large number of random variables ri(t), i = 1 ∼ M , representing the position vectors of M
particles from the origin of the volcanic vent. The gravitational fallout is superimposed on the process ofdiffusion and transportation.
With a discrete time increment ∆t, the Lagrangian form of the governing equation may be writtenaswhere ri=(x, y, z) is a position vector of the i-th particle at time t, V=(u, v, w) is the local wind velocity totransport the particle, Z=(ch, ch, cv ) is a diffusion vector containing diffusion speeds generated by Gaussian
random numbers, and G =(0, 0, −wG) is the gravitational fallout speed approximated by Stokes Law. Notethat diffusion Z depends on the direction, and gravity settling G depends on the particle size.
For computation of the transportation, wind velocity V is obtained from the real-time Grid Point
Values (GPV) data provided by the Japan Meteorological Agency (JMA). The GPV data contain initial andpredicted wind data up to 168 hours in the weather forecast by the global spectral model (GSM). The GPVdata with 6-hour intervals are first interpolated to the model's time step of 5 minutes by a cubic spline
method (see Burden et al., 1981). Then, the wind velocity at an arbitrary spatial point is evaluated using the
3D cubic-splines from the nearby gridded data of 1.25。longitude-latitude intervals and 16 vertical levels
from the surface up to 10 hPa. For the real-time PUFF model prediction, the forecasted wind data are used.
However, for the simulation in the past eruption event, the forecasted wind data have been replaced by asequence of initial data provided by the analysis-forecast cycle. The diffusion speed and gravitational
settling are described in detail by Tanaka et al. (2016). This paper can be referenced for details of the model
description. In this study, the particle size is given by the mean of -3.5 and standard deviation of 1.0 in a
log-normal distribution. The radius of enhanced diffusion is set at r0=70 km. All remaining parameters are
the same as those used in Tanaka et al. (2016).
As the source of ash plume S, the number of particles released at every time step may be adjusted
in order to draw optimal statistical information from the model products. In this study we generate M0=5000
particles uniformly in time by a uniform random number over time step ∆t, which scales the emission rate.
Particles are converted from the time coordinate to the vertical column from vent z1 to plume top z2
considering the buoyancy. In the present case, z1=657 m for the vent, and plume height z2 reached 9 km,
and the discharge was assumed for 10 min from the initial explosion. Since there is no reliable information
for the emission rate for this event, we must assume a uniform emission rate during the 10 min.
The governing model equation is integrated in time and the distribution of the particles in theatmosphere is presented in various mapping projections. The total number of plume particles M in theatmosphere increases by every time step. When the particles fall to the ground, the fallout locations arerecorded. Likewise, when the particles have moved out from the prescribed computing domain, they are
removed from the computation. The distribution of the ash fallout amount is computed by counting the total
number and total mass of the ashes at a unit area on the ground. The emission rate is then scaled in reference
to the ground observation at Yakushima Island (NIED 2015). Likewise, the distribution of the airborne ash
density is computed by counting the total number and total mass of the ashes at a unit volume in theatmosphere. The output product of the map projections is drafted using Generic Mapping Tools (GMT)
software (Wessel et al. 2013).

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3.

Results of the model simulation

The performance of the PUFF model simulation of the ash dispersal relies totally on the accuracy of thewind data provided by JMA/GSM. The output from GSM with 1.25°longitude-latitude grids is coarser thanthat of the meso-scale numerical weather prediction models. However, as it has the advantage of covering
the entire world, the PUFF model is applicable to any erupting volcano on the planet.
Figure 3 shows the wind vectors at 1000 hPa and 400 hPa levels at the time of 9:00 am (0:00 UTC)on 29 May 2015. The real-time GPV data is provided by the Japan Meteorological Agency by way of theportal site at the Center for Computational Sciences, University of Tsukuba. The 400 hPa map shows thata strong west-northwesterly wind of 14 m/s blows over Kuchinoerabujima at an altitude of 7.5 km. The air
moves 50 km/hour to the east-southeast, which is consistent with the satellite imagery in Fig. 2. The windnear the surface at the 1000 hPa level is in the opposite direction to the wind at the 400 hPa level.

Fig. 3 Wind vectors at 1000 hPa (near surface) and 400 hPa levels (about 7.5 km) at 00:00 UTC on 29 May
2015. The real-time GPV data is provided by the Japan Meteorological Agency by way of the Centerfor Computational Science, University of Tsukuba.
Figure 4 illustrates the results of the PUFF model simulation of the 3D perspective image of the
volcanic ash plume dispersal at 9:00 UTC on 29 May 2015. The figure is for 8 hours after the beginning of
the eruption. The colors of particles indicate a different plume height, and the projection onto the ground ismarked by black dots. Since the plume top reached 9 km, the strong west-northwest wind transports the ash
plume in the east-southeast direction. The plume tilts eastward with respect to height. As shown by the1000 hPa level winds in Fig. 3, the lowest level particles move in the opposite direction to the upper levelparticles.

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Fig. 4 The 3-D perspective image of the volcanic ash plume dispersal from Kuchinoerabujima Volcano at
8 hours after the eruption. The colors of particles indicate different plume height, and the projection
onto the ground is marked by black dots.
Figure 5 illustrates the results of horizontal distributions of the ash plume dispersal for 2, 4, 6, and8 hours after the eruption set at 1:00 UTC. The colors of particles indicate different plume heights in feet.
At 2 hours after the eruption, there is a circular-shaped plume top (red) by the horizontal diffusion. The
location of the ash plume agrees with the satellite imagery in Fig. 2. However, details of the ash distribution
and plume shape are rather different. In Fig. 2, the ash over Yakushima indicates a hook shape, but thesimulated ash indicates a circular shape. The wind data with 1.25°longitude-latitude grids is insufficientfor simulating details of the plume structure. Yet, the location of the simulated ash clouds agrees well withthe satellite observation.
As seen at 4 hours after the eruption, the ash plume has drifted in the east-southeast direction by thestrong west-northwest wind at an altitude of 7.5 km. Note that the low-level ash drifts westward (blue). The
result is consistent with the satellite observation in Fig. 2. At 6 hours, there is further drift of the plume top(red) to the southeast. The plume is the highest at the front edge of the movement, and the height decreases
at the source region. Interestingly, the lower part of the plume (blue) continues moving westward. At 8hours after the eruption, the plume top (red) is at 132. 5°E, which is about 250 km from the volcano.

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Figure 5(a)Figure 5(b)Figure 5(c)Figure 5(d)Fig. 5 PUFF model simulation of the ash plume dispersal for (a) 2 hours, (b) 4 hours, (c) 6 hours, and (d)8 hours after the eruption set at 1:00 UTC. The colors of particles indicate different plume heights.

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Figure 6 depicts the vertical cross sections of ash plume dispersal for longitude-height andmeridional-height sections for every 1 hour starting from the eruption. The plume shape for the first 1 hourshows a structure with minor spread at the plume top near 9 km both in the X-Z and Y-Z sections. The resultof the X-Z section shows a flat plume top extending eastward by the upper air wind. A minor counter flow
is seen at the lowest level by the counter flow in the boundary layer. Simulated animation shows there aremany particles falling from the anvil clouds at the east side. The result of the Y-Z section shows anvil clouds
extending south from the volcano forming a reverse triangle from the vent. The upper level plume extends
southward indicating a wedge shape.

Fig. 6 Vertical cross sections of ash plume dispersal for longitude-height and meridional-heightsections for every 1 hour starting from the eruption set at 1:00 UTC.
Figure 7(a) plots the particle distribution for ash fallout accumulated during the 9 hours following
the eruption. The fallout covers almost the entire Yakushima Island extending in the southeast direction.
According to the in-situ observations of ash fallout over Yakushima Island (NIED 2015), a maximum of
400 g/m2 of ash was reported at the western end of Yakushima Island, and 100 g/m2 of ash in the middle ofthe island.
Figure 7(b) plots the ash fallout distribution evaluated from Fig. 7(a) in the units of g/m2 with acommon log-scale, i.e., 2 denotes 100 g/m2. The contours of the PUFF model simulation are roughly
calibrated in reference to the in-situ observations to match each other. By this calibration, it is possible toassign a mass to the particle in the model. According to the result, we find that one particle in the model
represents 60 tons of mass for the emission rate of 5000 particles in 5 minutes. Based on this number, theemission rate is estimated as 60,000 tons per minute, and total emissions are estimated as 600,000 tons for
10 minutes of eruption in this event. Once a mass estimation is given to the particle, it becomes possible toassess the ash concentration in the air.

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Figure 7(a)Figure 7(b)Fig. 7 (a) Particle distribution of ash fallout during 9 hours after the eruption, and (b) the estimatedconcentration of ash fallout (g/m2) in common log-scale, i.e., 2 denotes 100 g/m2.
Finally, Fig. 8 plots the distributions of airborne ash density (mg/m3) for 2, 4, 6, and 8 hours after
the eruption. The values are in common log-scale, i.e., 2 denotes 100 mg/m3. As a result, the values of thehighest density in the vertical column are projected onto the ground.
At 2 hours after the eruption, a circular-shaped ash plume is clearly identified. In the core region,
there is a contour of 100 mg/m3 over Yakushima Island. The contour of 0.6 represents the ash density of 4
mg/m3. This area is recognized as a danger zone for commercial airliners. It seems that the diffusion is ingood agreement in the present simulation compared with the satellite imagery in Fig. 2. At 4 hours after the
eruption, the core area with 100 mg/m3 is maintained. The area with 4 mg/m3 extends 150 km east from thevolcano. The area of ash density with 4 mg/m3 covers most regions of Yakushima Island and the southernedge of Tanegashima Island. At 6 hours after the eruption, the contour 100 mg/m3 has moved in thesoutheast direction around 132.0°E and 29.5°N. The area with 4 mg/m3 appears widely around 131.5°E
and 29.5°N , but Yakushima Island and Tanegashima Island are now out of the danger zone. Finally, at 8hours after the eruption, the area with 4 mg/m3 has moved further to the southeast around 132.5°E and29.3°N.
Although the satellite image in Fig. 2 shows the exact location of ash plume detectable by thesatellite, there is the possibility of a wider spread of thinner ashes as simulated by the present model. The
airborne ash density simulated by the PUFF model provides useful and quantitative information about thepossible danger zone for the eruption event of Kuchinoerabujima Volcano in May 2015.

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Fig. 84.

Figure 8(a)Figure 8(b)Figure 8(c)Figure 8(d)Distribution of airborne ash density (mg/m3) for (a) 2 hours, (b) 4 hours, (c) 6 hours, and (d) 8hours after the eruption. The values are in common log-scale, i.e., 2 denotes 100 mg/m3.

Conclusion

A major eruption occurred at Kuchinoerabujima Volcano at 9:59 am local time (0:59 UTC) on 29 May 2015.
The ash plume reached 9 km above the ground. According to the MTSAT-2 satellite monitoring, the plume
top approximately 9 km in height drifted in the east-southeast direction. The ash plume showed amushroom-shaped distribution heading in the east-southeast direction according to the satellite image. The
plume top drifted with a gradual spread by diffusive mixing. By 8 hours after the eruption, the center of the88

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plume top had drifted in the east-southeast direction by 250 km. In this study, the sequence of airborne ash
dispersal from Kuchinoerabujima Volcano was simulated using the PUFF model. A steady emission ratefrom the vent was assumed for 10 min.
The horizontal distribution of ash fallout was estimated by the model simulation and compared withthe ground truth observation in Yakushima Island. The ash fallout over Yakushima Island was in the orderof 100 g/m2. After some calibrations with this number, the mass of an ash particle in the model wasquantified to have 60 tons of ash mass. The result suggests that the ash concentration in the air can be
estimated by this method.
According to ICAO, ash density of 4 mg/m3 and above is considered a danger zone for commercial
airliners. The result of the PUFF model simulation suggests that the anvil cloud of ash top at 9 km maintains
sufficiently high ash density for 8 hours after the eruption. According to the result of the PUFF model
simulation, the core region of the plume front shows the airborne ash density of 100 mg/m3 even at 250 km
from the volcano.
Although the satellite images show the exact location of the ash plume, the simulation result
indicates a large diffused area of the danger zone for aircraft. The model prediction can provide information
for thin ash dispersal at a long distance, which the satellite data cannot detect. However, the accuracy of themodel prediction relies totally on the wind data by the numerical weather prediction models. The accurate
wind data and emission rate are the most important items for the improvement of the ash dispersal model.
In this study, the emission rate was scaled in reference to the ground observation at Yakushima Island. The
particle size and fallout speed are important to calibrate the emission rate with a few ground observations.
Further improvement is required for the PUFF model simulation by accumulating comparisons for theobservations and simulation outputs.

Acknowledgments
We are grateful for the support of Dr. H. Nakamichi of DPRI, Kyoto University and Mr. Mamoru Izumi of
SATREPS for their technical assistance. The MTSAT-2 satellite imagery was provided by the Japan
Meteorological Agency. This research was supported by the SATREPS research project and by Grant-inAids (15H05794) of the Japan Society for the Promotion of Science (JSPS).

References[1]Akasofu, S.-I., and H. L. Tanaka, 1993. Urgent issue of developing volcanic ash tracking model, Kagaku
Asahi, No.5, 121-124 (in Japanese).
[2]Casadevall, T. L., 1994. The 1989-1990 eruption of Redoubt volcano, Alaska: Impacts on aircraft
operations, J. Volcanol. Geotherm. Res., 62, 301-316.
[3]Chatfield, C., 1975. The analysis of time series: An introduction, Chapman and Hall, 286 pp.
[4]Dean, K. G., S. I. Akasofu, and H. L. Tanaka, 1993. Volcanic hazards and aviation safety: Developing
techniques in Alaska, FAA Aviation Safety Journal, Vol. 3, No. 1, 11-15.
[5]Hobbs, P. V., L. F. Radke, J. H. Lyons, R. J. Ferek, D. J. Coffman, and T. J. Casadevall, 1991. Airborne
measurements of particle and gas emissions from the 1990 volcanic eruption of Mount Redoubt, J.
Geophys. Res., 96, 18735-18752.
[6]Iguchi, M., 2012. Prediction of volume of volcanic ash ejected from Showa crater of Sakurajima Volcano,Japan, Disaster Prevention Research Institute, Annual Report B, University of Kyoto, 55, 169-175.
[7]Iguchi, M., 2016. Method for real-time evaluation of the discharge rate of volcanic ash: Case study onintermittent eruptions at Sakurajima Volcano, Japan, J. Disaster Res. 11, 1, 4-14.
[8]Kelleher, R., 2010. Atlantic conference on Eyjafjatlajokutl and aviation, UK volcanic ash safety
regulation, Keflavic Airport, Iceland.
[9]Kienle, J., A. W. Woods, S. A. Estes, K. Ahlnaes, K. G. Dean, and H. L. Tanaka, 1991. Satellite and89

H.L.TANAKA, M.IGUCHI

slow-scan television observations of the rise and dispersion of ash-rich eruption clouds from Redoubt
volcano, Alaska, EOS, Vol. 72, 2, 748-750.
[10]NIED Report, 2015. Report on ash fallout at Yakushima Island for volcanic eruption ofKuchinoerabujima on 29 May 2015, National Research Institute for Earth Science and Disaster
Resilience (NIED) on 5 June 2015, http://www.bosai.go.jp/saigai/2015/pdf/20150605-01.pdf (inJapanese).
[11]Onodera, S., 1997. Volcanic activity and flight operations, Aviation Meteorological Notes, 45, 13-30.
[12]Onodera, S., 2013. A study on the prevention of aircraft encounter with volcanic ash in the proximity
area between airways and active volcanoes, Dissertation for Ph. D., Life and Environmental Sciences,
University of Tsukuba, 272 pp.
[13]Searcy, C., K. Dean, and B. Stringer, 1998. PUFF: A volcanic ash tracking and prediction model, J.
Volc. and Geotherm. Res., 80(1-2), 1-16.
[14]Tanaka, H. L., 1991. Development of a prediction scheme for the volcanic ash fall from Redoubt
volcano, First Int'l. Symp. on Volcanic Ash and Aviation Safety, Seattle, Washington. U.S. Geological
Survey, Circular 1065, 58.
[15]Tanaka, H. L., K. G. Dean, and S. I. Akasofu, 1993. Predicting the movement of volcanic ash clouds,
EOS, Vol. 74, No. 20, 231-231.
[16]Tanaka, H. L., 1994. Development of a prediction scheme for volcanic ash fall from Redoubt volcano,
Alaska, Proc. First International Symposium on Volcanic Ash and Aviation Safety, U.S. Geological
Survey, Bulletin 2047, 283-291.
[17]Tanaka, H.L., and K. Yamamoto, 2002. Numerical simulations of volcanic plume dispersal from Usu
Volcano in Japan on 31 March 2000, Earth, Planets and Space, 54, 743-752.
[18]Tanaka, H.L., M. Iguchi, and S. Nakata, 2016. Numerical simulations of volcanic ash plume dispersal
from Kelud Volcano in Indonesia on February 13, 2014, J. Disaster Res. 11, 1, 31-42.
[19]Wessel, P., W. H. F. Smith, R. Scharroo, J. F. Luis, and F. Wobbe, 2013. Generic Mapping Tools:
Improved version released, EOS Trans, AGU, 94, 409-410.

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