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Titel |
Modeling transport and aggregation of volcanic ash particles |
VerfasserIn |
Antonio Costa, Arnau Folch, Giovanni Macedonio, Adam Durant |
Konferenz |
EGU General Assembly 2010
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 12 (2010) |
Datensatznummer |
250039511
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Zusammenfassung |
A complete description of ash aggregation processes in volcanic clouds is an very arduous
task and the full coupling of ash transport and ash aggregation models is still computationally
prohibitive. A large fraction of fine ash injected in the atmosphere during explosive eruptions
aggregate because of complex interactions of surface liquid layers, electrostatic
forces, and differences in settling velocities. The formation of aggregates of size
and density different from those of the primary particles dramatically changes the
sedimentation dynamics and results in lower atmospheric residence times of ash
particles and in the formation of secondary maxima of tephra deposit. Volcanic ash
transport models should include a full aggregation model accounting for all particle
class interaction. However this approach would require prohibitive computational
times. Here we present a simplified model for wet aggregation that accounts for both
atmospheric and volcanic water transport. The aggregation model assumes a fractal
relationship for the number of primary particles in aggregates, average efficiencies factors,
and collision frequency functions accounting for Brownian motion, laminar and
turbulent fluid shear, and differential settling velocity. We implemented the aggregation
model in the WRF+FALL3D coupled modelling system and applied it to different
eruptions where aggregation has been recognized to play an important role, such as
the August and September 1992 Crater Peak eruptions and the 1980 Mt St Helens
eruption. Moreover, understanding aggregation processes in volcanic clouds will
contribute to mitigate the risks related with volcanic ash transport and sedimentation. |
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