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

3W_4C-P8

Date/Time: July 23 Poster

Sensitivity study of numerical weather-model parameters for quantitatively estimating
ash concentration in the atmospheric surface layer with a computational ash dispersion
model, FALL3D
Yasuo Hattori1 , Hitoshi Suto1 , Yumiko Go2 , Kiyoshi Toshida1 , Hiromaru Hirakuchi1 , Shuji Ishihara11Central Research Institute of Electric Power Industry, Japan, 2 Denryoku Computing Center, Japan
E-mail: yhattori@criepi.denken.or.jp

An estimation of ash concentration in the atmospheric surface layer, which is the lower part of the planetary
boundary layer (PBL), is of practical interest in discussion on volcanic ash impacts on critical infrastructure. For
estimating ash concentration in the atmosphere, numerical simulations with an ash transport- and deposition-model
have become a powerful tool (e.g. Folch 2012). However, the performance of such simulations for the surface layer
has not fully understood, while that for the atmosphere and the ground deposition have been actively examined.
This might due to the complicated interaction between the ass dispersion- and meteorological-processes near theground, suggesting that the accurate description of meteorological condition must be vital for such simulations.
Thus, we have carried out sensitivity study of numerical-weather model parameters for predicting the ash
concentration in the atmospheric surface layer in the present study.

We consider a test case corresponding to the eruption at Mt. Shinmoe-dake on January 2011; the eruption
column height is approximately 8000m and the total mass flow rate is about 5e9 kg during 2 hr.
We have used two models to examine the interaction between dispersion- and meteorological- processes: oneis the CRIEPI weather forecasting and analysis system, NuWFAS, which consist of a numerical weather model,
WRF, and some pre- and post-processing tools; the other is an ash transport- and deposition-model, Fall3D. In
the numerical weather simulations with NuWFAS, the horizontal- and vertical-grid spacing is varied from 2.5 km to
10km and from 100 m to 500 m, respectively, to check the grid dependency. Two PBL scheme is used to discuss
the implications for the turbulence diffusion coefficient in the planetary boundary layer.

After verifying the capability of this setup through the comparison with the observations of isomap of ash
deposition, we discuss the predicted ash concentration in the atmospheric surface layer in detail; the time-seriesof ash concentration near the ground, especially near the vent, depict complex wave forms and there values
fluctuates; this is due to the change in the advection and turbulence diffusion processes of volcanic ash. The
numerical-weather prediction parameters decidedly affect wind speed and directions and also turbulence diffusion
coefficients in the PBL, which have important roles in the advection and diffusion processes.

Thus, suchparameters have also effects on quantitative estimation of ash concentrations in the surface layer.

More details will be presented in a full paper, and we believe that our study must be helpful to develop
computational ash transport- and deposition-models.

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