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| Titel |
The impact of the characteristics of volcanic ash on forecasting. |
| VerfasserIn |
Frances Beckett, Matthew Hort, Sarah Millington, John Stevenson, Claire Witham |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250072935
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| Zusammenfassung |
| The eruption of Eyjafjallajökull during April – May 2010 and Grímsvötn in May 2011,
Iceland, caused the widespread dispersion of volcanic ash across the NE Atlantic, and
ultimately into UK and European airspace. This resulted in thousands of flights to
and from affected countries across Europe to be cancelled. The Met Office, UK, is
the home of the London VAAC, a Volcanic Ash Advisory Centre, and as such is
responsible for providing reports and forecasts for the movement of volcanic ash
clouds covering the UK, Iceland and the north-eastern part of the North Atlantic
ocean.
To forecast the dispersion of volcanic ash requires that the sedimentation of ash particles
through the atmosphere is effectively modelled. The settling velocity of an ash particle is
a function of its size, shape and density, plus the density and viscosity of the air
through which it is falling. We consider the importance of characterising the physical
properties of ash when modelling the long range dispersion of ash particles through the
atmosphere. Using the Reynolds number dependent scheme employed by NAME, the
Lagrangian particle model used operationally by the Met Office, we calculate the
settling velocity and thus the maximum travel distance of an ash particle through an
idealised atmosphere as a function of its size, shape and density. The results are
compared to measured particle sizes from deposits across Europe following the
eruption of Eyjafjallajökull in 2010. Further, the particle size distribution (PSD) of
ash in a volcanic cloud with time is modelled using NAME: the particle density
distribution and particle shape factor are varied and the modelled PSD compared
to the PSD measured in the ash cloud during the eruption of Eyjafjallajökull in
2010 by the FAAM research aircraft. The influence of the weather on PSD is also
considered by comparing model output using an idealised atmosphere to output using
NWP driven meteorological fields. We discuss the sensitivity of forecasts of the
dispersion of volcanic ash to the representation of particle characteristics in NAME, the
importance of representing the weather in ash fall models, and the implications of these
results for the operational forecasting of volcanic ash dispersion at the London
VAAC. |
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