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| Titel |
Source mass eruption rate retrieved from satellite-based data using statistical modelling |
| VerfasserIn |
Mathieu Gouhier, Arnaud Guillin, Nourddine Azzaoui, Julia Eychenne, Sébastien Valade |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250110244
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| Publikation (Nr.) |
 EGU/EGU2015-10222.pdf |
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| Zusammenfassung |
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\begin{document}
{\raggedright
Ash clouds emitted during volcanic eruptions have long been recognized as a
major hazard likely to have dramatic consequences on aircrafts, environment and
people. Thus, the International Civil Aviation Organization (ICAO) established
nine Volcanic Ash Advisory Centers (VAACs) around the world, whose mission is to
forecast the location and concentration of ash clouds over hours to days, using
volcanic ash transport and dispersion models (VATDs). Those models use input
parameters such as plume height (PH), particle size distribution (PSD), and mass
eruption rate (MER), the latter being a key parameter as it directly controls the
amount of ash injected into the atmosphere. The MER can be obtained rather
accurately from detailed ground deposit studies, but this method does not match
the operational requirements in case of a volcanic crisis. Thus, VAACs use
empirical laws to determine the MER from the estimation of the plume height. In
some cases, this method can be difficult to apply, either because plume height
data are not available or because uncertainties related to this method are too
large. We propose here an alternative method based on the utilization of
satellite data to assess the MER at the source, during explosive eruptions.
Satellite-based techniques allow fine ash cloud loading to be quantitatively
retrieved far from the source vent. Those measurements can be carried out in a
systematic and real-time fashion using geostationary satellite, in particular. We
tested here the relationship likely to exist between the amount of fine ash
dispersed in the atmosphere and of coarser tephra deposited on the ground. The
sum of both contributions yielding an estimate of the MER. For this purpose we
examined 19 eruptions (of known duration) in detail for which both (\textit{i})
the amount of fine ash dispersed in the atmosphere, and (\textit{ii}) the mass of
tephra deposited on the ground have been estimated and published. We combined
these data with contextual information that may influence the statistical
relationship such as the magma composition or the existence of phreatomagmatism.
In order to infer the relationship between ash content in the atmosphere and the
amount of tephra on the ground, we used advanced statistic modelling using model
selection, with AIC-type (Akaike Information Criterion) penalization, and
classification. First we show that a reliable statistical relationship does exist
between atmospheric fine ash and tephra fall deposits. Then we show that magma
composition does have an effect on this relationship. It follows a power function
in the form $S_1=c_0{S_2}^{c_1\left(P_n\right)}H^{c_2}$ having a coefficient of
determination r$^{2}$=0.91 and a prediction error of 2.16 at a confidence level
of 95\%. \textit{S$_{1}$} is the mass of tephra fall deposits and
\textit{S$_{2}$} is the fine ash cloud mass as retrieved from satellite
measurements. \textit{H} is the plume height, c$_{0}$ and c$_{2}$ are constant
coefficients while c$_{1}$ is variable and depends on the magma composition type
(\textit{P$_{n=1:3}$}). This method greatly improves the prediction capability of
the source MER as compared to the one based on the plume height solely. If
available in real-time, satellite data might be advantageously used as a proxy by
the VAACs, to derive key source parameters such as the MER.
}
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