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| Titel |
Long-range transport of dust and smoke towards and over the Amazon rain forest observed with lidar during the wet and dry season |
| VerfasserIn |
Holger Baars, Dietrich Althausen, Ronny Engelmann, Detlef Müller, Albert Ansmann, Paulo Artaxo, Theotonio Pauliquevis, Rodrigo Souza, Scot Martin |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250055231
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| Zusammenfassung |
| The Amazon basin with its extensions of more than six million square kilometres contains the
world’s largest tropical rain forest. Investigations of aerosol characteristics in this
large area are important for the understanding of the local and global influence of
Amazonian aerosol on radiation budget and cloud formation. Compared to its global
importance, knowledge of the vertical distribution of aerosols in this region is still
inadequate. For the first time in Amazonia, long-term observations of the vertical aerosol
structure were made with a multi-wavelength Raman lidar. These measurements were
performed with the automated polarization-Raman lidar PollyXT of the Leibniz
Institute for Tropospheric Research (IfT) in the framework of the European Integrated
project on Aerosol Cloud Climate and Air Quality Interactions (EUCAARI) and the
Amazonian Aerosol Characterization Experiment (AMAZE-08). The almost continuous
measurements were taken near Manaus, Brazil (2Ë S, 60Ë W) from January to November
2008. With PollyXT, vertical profiles of the backscatter coefficient at 355 nm, 532
nm, and 1064 nm, of the extinction coefficient at 355 nm and 532 nm, and of the
particle depolarization ratio at 355 nm can be determined. Microphysical aerosol
properties like effective radius and volume concentration are calculated from the
optical properties with an inversion algorithm. In total, more than 2500 hours of
observations on 211 days were made during the wet (November-May) and dry season
(June-October). Back-trajectory calculations have been used to define the origin of the
air masses at different height levels. The analysis of these observations reveals
that intrusions of biomass burning aerosol from Africa in association with Saharan
dust could be observed frequently during the wet season. The separation of dust
and smoke in the lidar backscatter profiles by depolarization quantities showed
that the dust fraction in the African aerosol plumes is less than 40% during the
months with high fire activity in Central Africa (January-April). When long-ranged
transported aerosol was absent, very clean conditions in terms of aerosol were observed.
Usually heavy mesoscale precipitation events took place before these observations.
The aerosol optical thickness at 532 nm was then below 0.02. In contrast to these
clean cases, aerosol conditions during the dry season are dominated by the high fire
activity on the South American continent. The fires occur usually at the edges of the
Amazon rain forest and are then transported towards the interior regions of the Basin
within some days. Thus, aerosol conditions at the lidar site were dominated by
aged biomass-burning aerosol during this season. In general a much higher, but
highly variable aerosol load in comparison to the wet season was observed. High
vertical aerosol variability was observed during that season, too, as well as the
frequent occurrence of lofted aerosol layers. The maximum observed values of the
extinction coefficient at 532 nm were about 350 Mm-1. These high values were
usually observed in connection with hygroscopic growth at around 2000 m agl. The
statistical analysis of the observations also reveals that the aerosol-layer top in the dry
season is typically between 3000 and 4500 m, but also reaches maximum values
up to 5500 m. In the wet season, the aerosol layer top is usually well below 3000
m.
EUCAARI is funded by the European Union (Framework Program 7, grant 036833-2). |
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