Presenter/Author Information

Naoko Seino
Hidetaka Sasaki
Junji Sato
Masaru Chiba

Keywords

nonhydrostatic model, multi-nesting, dispersion modelling, volcanic so2

Start Date

1-7-2002 12:00 AM

Description

After severe eruptions of the volcano at Miyake Island in August 2000, a large amount of volcanic gas has been released into the atmosphere. To simulate flows and dispersion of SO2 gas over the Miyake Island, a set of numerical models was developed. The multi-nesting method was adopted to reflect realistic meteorological field and to sufficiently resolve the flow over the island with a diameter of 8km. The outermost model was the Regional Spectral Model (RSM) of the Japan Meteorological Agency (JMA) with a horizontal grid size of 10km. Finer atmospheric structure was simulated with the nonhydrostatic model jointly developed by the Meteorological Research Institute and the Numerical Prediction Division of JMA (MRI/NPD-NHM) with grid intervals of 2km, 400m and 100m. Lagrangian particle model was applied to the dispersion model, which is driven by the meteorological field of the 100m-grid MRI/NPD-NHM. The random walk procedure was used to represent the turbulent diffusion. The model was verified in four cases. Simulated SO2 concentrations agreed well with observed concentrations at a monitoring station including temporal variation. Under a large synoptic change, however, accurate prediction became difficult. To further investigate the characteristics of the flow and the distribution of SO2, numerical experiments have been done. Steady inflows, classified according to surface wind speed and direction, were assumed. Simulated SO2 distribution on the ground apparently depends on the surface wind. Under relatively weak inflow, there is a large diurnal change in the SO2 distribution, affected by the thermally induced flow. The SO2 gas is widely spread downstream in the nighttime but hardly reaches the coastal area in the daytime. On the other hand, little diurnal variation could be seen under the stronger inflow. Ground temperature, as well as the static stability of the inflow, also influences downstream wind, turbulent diffusivity and the SO2 distribution.

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Jul 1st, 12:00 AM

High-resolution Simulation of Flow and Dispersion of Volcanic SO2 over the Miyake Island

After severe eruptions of the volcano at Miyake Island in August 2000, a large amount of volcanic gas has been released into the atmosphere. To simulate flows and dispersion of SO2 gas over the Miyake Island, a set of numerical models was developed. The multi-nesting method was adopted to reflect realistic meteorological field and to sufficiently resolve the flow over the island with a diameter of 8km. The outermost model was the Regional Spectral Model (RSM) of the Japan Meteorological Agency (JMA) with a horizontal grid size of 10km. Finer atmospheric structure was simulated with the nonhydrostatic model jointly developed by the Meteorological Research Institute and the Numerical Prediction Division of JMA (MRI/NPD-NHM) with grid intervals of 2km, 400m and 100m. Lagrangian particle model was applied to the dispersion model, which is driven by the meteorological field of the 100m-grid MRI/NPD-NHM. The random walk procedure was used to represent the turbulent diffusion. The model was verified in four cases. Simulated SO2 concentrations agreed well with observed concentrations at a monitoring station including temporal variation. Under a large synoptic change, however, accurate prediction became difficult. To further investigate the characteristics of the flow and the distribution of SO2, numerical experiments have been done. Steady inflows, classified according to surface wind speed and direction, were assumed. Simulated SO2 distribution on the ground apparently depends on the surface wind. Under relatively weak inflow, there is a large diurnal change in the SO2 distribution, affected by the thermally induced flow. The SO2 gas is widely spread downstream in the nighttime but hardly reaches the coastal area in the daytime. On the other hand, little diurnal variation could be seen under the stronger inflow. Ground temperature, as well as the static stability of the inflow, also influences downstream wind, turbulent diffusivity and the SO2 distribution.