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| Titel |
Volcanic ash from Iceland over Munich: mass concentration retrieved from ground-based remote sensing measurements |
| VerfasserIn |
J. Gasteiger, S. Groß, V. Freudenthaler, M. Wiegner |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 11, no. 5 ; Nr. 11, no. 5 (2011-03-11), S.2209-2223 |
| Datensatznummer |
250009456
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| Publikation (Nr.) |
 copernicus.org/acp-11-2209-2011.pdf |
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| Zusammenfassung |
| Volcanic ash plumes, emitted by the Eyjafjallajökull volcano (Iceland) in
spring 2010, were observed by the lidar systems MULIS and POLIS in Maisach
(near Munich, Germany), and by a CIMEL Sun photometer and a JenOptik
ceilometer in Munich. We retrieve mass concentrations of volcanic ash from
the lidar measurements; spectral optical properties, i.e. extinction
coefficients, backscatter coefficients, and linear depolarization ratios, are
used as input for an inversion. The inversion algorithm searches for model
aerosol ensembles with optical properties that agree with the measured values
within their uncertainty ranges. The non-sphericity of ash particles is
considered by assuming spheroids. Optical particle properties are calculated
using the T-matrix method supplemented by the geometric optics approach. The
lidar inversion is applied to observations of the pure volcanic ash plume in
the morning of 17 April 2010. We find 1.45 g m−2 for the ratio between
the mass concentration and the extinction
coefficient at λ = 532 nm, assuming an ash density of 2.6 g cm−3.
The uncertainty range for this ratio is from 0.87 g m−2 to
2.32 g m−2. At the peak of the ash concentration over Maisach the
extinction coefficient at λ = 532 nm was 0.75 km−1
(1-h-average), which corresponds to a maximum mass concentration of
1.1 mg m−3 (0.65 to 1.8 mg m−3). Model calculations show that
particle backscatter at our lidar wavelengths (λ ≤ 1064 nm), and
thus the lidar retrieval, is hardly sensitive to large particles
(r ≳ 3 μm); large particles, however, may contain
significant amounts of mass. Therefore, as an independent cross check of the
lidar retrieval and to investigate the presence of large particles in more
detail, we model ratios of sky radiances in the aureole of the Sun and
compare them to measurements of the CIMEL. These ratios are sensitive to
particles up to r ≈ 10 μm. This approach confirms the
mass concentrations from the lidar retrieval. We conclude that synergistic
utilization of high quality lidar and Sun photometer data, in combination
with realistic aerosol models, is recommended for improving ash mass
concentration retrievals. |
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