1. Assessing Volcanic Ash Hazard by Using the CALPUFF System
The 2nd International Conference on Volcanic Ash and Aviation Safety June 21-24, 2004 Alexandria, Virginia (USA)
Assessing Volcanic Ash Hazard by Using the CALPUFF System
S.Barsotti*, A.Neri*, J.Scire**
*Istituto Nazionale di Geofisica e Vulcanologia,
Centro per la Modellistica Fisica e Pericolosità dei Processi Vulcanici, Pisa, Italy
**Earth Tech, Inc., Concord, Massachusetts, USA

2. Outline Motivation and objective
The CALPUFF modeling system structure (geophysical pre-processors, meteo diagnostic code CALMET and the dispersion code CALPUFF)
Results of a preliminary application of CALPUFF to the July 2001 Mt.Etna’s eruption
Conclusive remarks

3. Motivation
During the last eruptions of Mt.Etna (2001 and 2002) the relatively minor explosive activity renewed the interest in the volcanic risk due to the presence of ash in the atmosphere
Objective
To develope a predictive modeling tool - able to forecast the movement and properties of an ash cloud in the atmosphere - to be used during a volcanic crisis

4. CALPUFF Modeling System (Scire et al. 2000)
Developed in the 90’s by Sigma Research Corporation (now part of the Earth Tech, Inc.) as air quality modeling system
Proposed by U.S. EPA as a Guideline model for regulatory applications
System Flowchart
Meteo data
(MM5 or CALETA)
Terrain elevation data
(TERREL)
Landuse data
(CTGPROC)
CALMET(diagnostic meteo processor)
Emission data
CALPUFF (Lagrangian dispersion code)

5. CALMET (diagnostic meteo processor)
Input data: P, Elevation m.s.l, T, wind direction, wind speed, vertical velocity, relative humidity at different levels and every three hours
Output data: U, V, W wind components, T and all the micrometeorological variables on a specified grid and every hour
HOW DOES IT WORK?
Prognostic code output
Initial guess field
Refinement by interpolation
Correction by orography
Divergence minimization
Terrain effects
Step 1 wind field
Weighted observed data
Divergence minimization
Objective analysis
Step 2 wind field

6. CALPUFF
It is a Lagrangian dispersion model that treats the emitted material as a sequence of packets, or puffs, containing discrete quantity of particles. Each puff is then described with a Gaussian distribution and subjected to advection, diffusion and gravity
Selected a set of receptors, gridded or discrete, in the domain investigated, CALPUFF computes hourly the concentration and flux of particles at these points
Main features:
Different granulometric classes
Time dependent emission and meteo data
Dry and wet deposition
Buoyant area source
Domain from tens of ms to hundreds of kms
from the source

7. The basic equation
is the material mass in the puff and is a function of the sampling interval. Its variations are due to removal and to chemical processes.
The sigmas are the horizontal Gaussian dispersion coefficients and are functions of the sampling interval. They include effects of atmospheric turbulence, plume buoyancy and lateral (crosswind) scale of an area-source.
is the vertical term of the Gaussian distribution. It takes account for the vertical diffusion due to the mixing lid and plume buoyancy and is a function of the distance from the source.

8. Area Source Plume Rise
One of the main features of CALPUFF is the capability of treating the case of very hot area source. Using a file containing all the information related to the source, the code solves the three fundamental equations of conservation of mass, momentum and energy.
The equation system is (Weil 1988):

9. A First Volcanological Application (Etna July 2001)
Simulation parameters
Computational domain
Cell numbers 100X100
Δgrid=2km
Grid origin xUTM(km) =
yUTM(km) =
Period
20-24 July 2001
Geo and meteo input data
GTOPO Global data ~900m res.
USGS Global land-use data set ~900m res.
ECMWF meteo data 2.5*2.5 degree res.
NOAA meteo data 2.5*2.5 degree res.

10. Coltelli and Macedonio, GNV Ass. 2001
Source data
Coltelli and Macedonio, GNV Ass. 2001
For the rising plume:
Exit velocity m/sec
Exit temperature °C
Initial radius m
Ground elevation m
Emission height a.g m
Photo by Boris Bencke
For the puff description:
Particles diameter µm
Particles density kg/m^3
Emission rate ^2-10^3 kg/sec
Photo by Tom Pfeiffer

11. General features of ash dispersal
Ash concentration on air (Kg/m^3)

12. Temporal Evolution of the Emission Point
The code computes the effective height and the downwind distance from the vent where a puff description of the emission begins

13. Ash Cloud Concentration (1) Vertical distribution of ash concentration along the dispersal axis
Vertical distribution of particle concentration at a fixed time and different distances from the vent
Temporal evolution of the vertical concentration at 25 km from the vent

14. The sensitivity to meteo data
Image acquired by SeaStar Satellite at 1100UTC on 20July 2001
NOAA
ECMWF
Concentration (kg/m^3) on air summed on different vertical levels
Vertical distribution of wind direction

15. The sensitivity to meteo data
Image acquired by SeaStar Satellite at 1129UTC on 22July 2001
NOAA
ECMWF
Concentration (kg/m^3) on air summed on different vertical levels
Vertical distribution of wind direction

16. Conclusive Remarks
CALPUFF is a promising system for real-time forecast of volcanic ash dispersal produced by weak explosive activity
High resolution meteo data and accurate description of plume rise are critical for a correct modeling of plume dispersal
Definition of well-known test cases is fundamental for the validation of the code with observed data
Real-time measurements of the eruption plume and dispersal are crucial in order to obtain reliable forecasts