1991 Pinatubo Volcanic Simulation
Using ATHAM Model
Song Guo, William I Rose, Gregg J S Bluth
Michigan Technological University, Houghton, Michigan
Co-Workers
Christiane Textor1, Hans-F. Graf1, Michael Herzorg2
1Max-Planck Institute for Meteorology, Hamburg, Germany
2University of Michigan, Ann Arbor, Michigan
Photos of Volcanic Plume from Mt. Pinatubo Eruption
Outline
• Introduction and Motivation
• Summary of initial input parameters for
ATHAM model simulation
• Simulation results from model ATHAM
• Comparison with satellite observation
• Future Work and Outlook
Introduction and Motivation
• Why is remote sensing useful to study
volcanic plumes and their interaction with
the atmosphere?
• Why is modeling work needed to study
volcanic plumes and their interaction with
atmosphere?
Why Pinatubo? (Objective)
• Pinatubo eruption is the largest eruption of
the satellite remote sensing era (Hourly
GMS, AVHRR, TOMS)
• Pinatubo eruption had the largest global
environmental and climatic impacts
• Pinatubo eruption had the largest impact on
stratospheric ozone depletion
Objective (continue)
•Some results from ATHAM can be
compared
with satellite observations
– shape of the plume
– movement of the plume
– gas phase SO2 amount
– gas and particle separation
• Some model results cannot be measured by
satellite observations
- H2O entrained from the ambient
air
- microphysics process
- ash-hydrometer aggregation
- volcanic gas scavenging
Brief Introduction to ATHAM
(Active Tracer High Resolution Atmospheric Model)
• 3d formulated (2d Cartesian coordinates, 2d
cylindrical coordinates)
• 127 × 127 (× 127) grid points
• model domain: 50 km vertical, 200 km
horizontal
• simulation time: several hours
Brief Introduction to ATHAM
(Assumptions)
• Dynamic equilibrium
• Thermal equilibrium
• Ash is an active cloud or ice condensation
nuclei
• Ash is covered with water or ice is treated
as a pure hydrometeors
Brief Introduction to ATHAM
(Modules)
• Dynamics: transport of gas-particle-mixture
including tracers (advection and
thermodynamics)
• Turbulence: entrainment of ambient air
• Microphysics: development of ashhydrometeorss
• Scavenging: redistribution of volcanic gases
in hydrometeors
GMS Images Showing the Growth and Movement of Volcanic Plume
from Holasek et al., 1996, JGR, Vol. 101, No. B12, 27,635-27,655
• The Plume is quite
symmetrical for ~ 2-3
hrs after eruption
• The Plume expends
~100km/hr
(~80km/hr)for the
first (second) hour
after eruption
• The Plume is
heavily influenced by
Typhoon Yuya after
2-3 hrs after eruption
Summary of Input Parameters to ATHAM
2d cylindrical coordinate simulation is used:
Ash size distribution:
• simulation time : 120 min.
• 2 classes of gamma distribution
• duration of eruption: 180 min
• radius of smaller ash particle: 25m
Geometry of the volcano:
• radius of larger ash particle: 90m
• mountain height: 1200m
Weight percentage:
• diameter of the crater: 680m
• small and large particles : 46% each
Volcanic forcing:
• gas (water vapor): 8% (6.4%)
• magma temperature: 1073K
Atmospheric Profile:
• eruption velocity: 360 m/s
• no real time observation
• mass eruption rate: 4.5×108kg/s
• combine pre-eruption in-situ and
nearby real-time sounding observation
(no hurricane effect is considered for
first 2 hours simulation)
• density of ash: 1100 kg/m3
Sounding Profiles
Temperature
Relative Humidity
Wind Speed
Standard Tropical Profile
Mt. Pinatubo Volcanic Plume Altitude from
Holasek et al., (1996)
Highest Plume Altitude from ATHAM Simulation
Vertical Wind Distribution with the Larger Plume Height Simulation
Vertical Wind Distribution with Pinatubo Initial Conditions (19 min.)
In Situ Temperature Anomalous after 6 minutes of eruption
Total Ash Particles (19 minutes after eruption)
Total Ash Particles after 55 minutes of eruption
Total Ash Particles after 115 minutes of eruption
Ash Particle Results After 19 Minutes Eruption
(a) Sum Small Ash
© Gas Fraction
(b) Sum Large Ash
(d) Ice
Ash Particle Results after 55 Minutes of Eruption
(a) Sum Small Ash
© Gas Fraction
(b) Sum Large Ash
(d) Ice
Ash Particle Results After 115 Minutes of Eruption
(a) Sum Small Ash
© Gas Fraction
(b) Sum Large Ash
(d) Ice
Schematic of Microphysics Processes in Volcanic Plume
Hydrometeor Results After 19 Minutes of Eruption
(a) Water Vapor
© Cloud Ice
(b) Cloud Water
(d) Graupel
Hydrometeor Results After 55 Minutes of Eruption
(a) Water Vapor
© Cloud Ice
(b) Cloud Water
(d) Graupel
Hydrometeor Results After 115 Minutes of Eruption
(a) Water Vapor
© Cloud Ice
(b) Cloud Water
(d) Graupel
SO2 Scavenging Results After 19 Minutes of Eruption
(a) gas phase SO2
© SO2 in cloud ice
(b) SO2 in cloud water
(d) SO2 in graupel
SO2 Scavenging Results After 55 Minutes of Eruption
(a) gas phase SO2
(b) SO2 in cloud water
© SO2 in cloud ice
(d) SO2 in graupel
SO2 Scavenging Results After 115 Minutes of Eruption
(a) gas phase SO2
© SO2 in cloud ice
(b) SO2 in cloud water
(d) SO2 in graupel
Summary of intermediate results
• Ice phase hydrometeors (ash-hydrometeor aggregations)
are dominant, larger ash particles travel horizontally faster
than small ones
• The Plume’s horizontal travelling velocity (most probably
caused by gravity) is quite consistent with the satellite
image
• Gas phase volcanic gases (SO2, HCl, H2S) coexist with
different gas-hydrometeor mixtures
• Vertical falling particle velocity increases due to the ashhydrometeor aggregation
Summary of intermediate results (continue)
• No significant gas-particle separation is observed.
• Possible explanations:
- 2d symmetrical simulation (no wind effect included)
- simulation time is too short
- no typhoon Yunya influence yet
• Plume height is lower than Holasek et al. (1996) suggest.
• Possible explanations:
- according to the dynamic, turbulent, microphysics processes considered,
the plume cannot reach ~40km with the known eruption rate
- uncertainties from initial input conditions (atmospheric temperature
profile, vent temperature and diameter, weight percentage …)
Outlook and Future Work
• 2d cartesian coordinate simulation (wind effect) is needed, especially for
longer simulation with potential influence from typhoon Yunya
• 3d simulation is necessary for a more realistic and better description
• assemble and confirm initial input conditions more precisely, with
sensitivity tests to match the plume with the satellite results
• laboratory study of incorporation and adsorption of volcanic gases into
ash-hydrometeor aggregates
• comparison of gas phase SO2 with TOMS results, and considering SO2
releases due to ice sublimation, to study the variation and fate of SO2 in
the volcanic cloud
• comparison of ash property results with AVHRR and TOMS results
more in detail
• study the large particle removal rate by increasing the particle size
• if possible, use a regional chemical model to further study SO2
transportation
• add more tracers (?)