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| Titel |
Airborne lidar observations of volcanic ash during the eruption of Eyjafjallajökull in Spring 2010 |
| VerfasserIn |
F. Marenco, B. Johnson, K. Turnbull, J. Haywood, S. Newman, H. Webster, M. Cooke, J. Dorsey, H. Ricketts, L. Clarisse |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250061023
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| Zusammenfassung |
| The London Volcanic Ash Advisory Centre (VAAC), based at the Met Office,
provided forecast guidance for the Civil Aviation Authority during the eruption of
Eyjafjallajökull in April-May 2010. Besides providing daily forecasts using the Numerical
Atmospheric-dispersion Modelling Environment (NAME), a series of observational
activities were carried out by the Met Office, involving ground-based lidars, the
exploitation of satellite data, and research flights using the Facility for Airborne
Atmospheric Measurements BAe-146 research aircraft (FAAM, www.faam.ac.uk), on
which this talk is focused. Due to safety restrictions, aircraft sampling has only been
performed in areas where ash concentrations where forecasted to be less than 2000
μg/m3.
Volcanic ash layers were observed using an elastic backscatter lidar on-board the FAAM
aircraft operating at 355 nm, which allowed detailed mapping of the plumes. A flight on 4
May overpassed the ground-based lidar in Aberystwyth a few times. This provided ground
truth validation of the on-board lidar and of its data inversion procedure. The ash layer during
this flight was found to be in patches of short horizontal extent, but despite the strong
horizontal inhomogeneity the two lidars showed excellent qualitative and quantitative
agreement. Moreover, radiative transfer computations using the lidar-derived profiles of
aerosol extinction led to a good reconstruction of observed radiance spectra with on-board
spectrometers.
Aircraft in situ measurements of the particle size-distribution permitted the evaluation of
a coarse extinction fraction (ranging 0.5-1) and a coarse mode specific extinction (0.6-0.9
m2/g) for six research flights. These quantities were then used to convert the lidar-derived
aerosol extinction to ash concentration (with an estimated uncertainty of a factor of
two).
The combination of lidar and in-situ sampling of aerosol properties has thus offered us the
opportunity to compile a dataset of the airborne Eyjafjallajökull ash: whereas the in-situ
instrumentation provided a good insight into the microphysics, the lidar permitted mapping
the ash layers with excellent detail in two dimensions (the vertical and the along-track
horizontal). As data of airborne volcanic ash concentrations are rather limited, this dataset is
considered invaluable for validation of dispersion models and satellite products. We will
briefly show here how these estimates of ash concentration compare with forecast maps
obtained with the NAME model and with satellite retrievals of ash column load obtained with
IASI and SEVIRI.
Acknowledgments: Airborne data was obtained using the BAe-146-301 Atmospheric
Research Aircraft (ARA) flown by Directflight Ltd. and managed by the Facility for Airborne
Atmospheric Measurements (FAAM), which a joint entity of the Natural Environment
Research Council (NERC) and the Met Office. |
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