Unexpected vertical structure of the Saharan Air Layer and giant dust particles during AER-D
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Published:2018-12-12
Issue:23
Volume:18
Page:17655-17668
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ISSN:1680-7324
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Container-title:Atmospheric Chemistry and Physics
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language:en
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Short-container-title:Atmos. Chem. Phys.
Author:
Marenco FrancoORCID, Ryder ClaireORCID, Estellés Victor, O'Sullivan Debbie, Brooke JenniferORCID, Orgill Luke, Lloyd Gary, Gallagher MartinORCID
Abstract
Abstract. The Saharan Air Layer (SAL) in the summertime eastern Atlantic is
typically well mixed and 3–4 km deep, overlying the marine boundary layer
(MBL). In this paper, we show experimental evidence that at times a very
different structure can be observed. During the AERosol properties – Dust (AER-D) airborne campaign in
August 2015, the typical structure described above was observed most of the
time, and was associated with a moderate dust content yielding an aerosol
optical depth (AOD) of 0.3–0.4 at 355 nm. In an intense event, however, an
unprecedented vertical structure was observed close to the eastern boundary
of the basin, displaying an uneven vertical distribution and a very large AOD
(1.5–2), with most of the dust in a much lower level than usual (0.3–2 km).
Estimated dust concentrations and column loadings for all flights during the
campaign spanned 300–5500 and 0.8–7.5 g m−2,
respectively. The shortwave direct radiative impact of the intense dust event
has been evaluated to be as large as -260±30 and -120±15 W m−2 at the surface and top of atmosphere (TOA), respectively. We also
report the correlation of this event with anomalous lightning activity in the
Canary Islands. In all cases, our measurements detected a broad distribution of
aerosol sizes, ranging from ∼0.1 to ∼80 µm (diameter), thus highlighting the presence of giant particles.
Giant dust particles were also found in the MBL.
We note that most aerosol models may miss the giant particles
due to the fact that they use size bins up to 10–25 µm.
The unusual vertical structure and the giant particles may have
implications for dust transport over the Atlantic during intense
events and may affect the estimate of dust deposited to the ocean.
We believe that future campaigns could focus more on events with
high aerosol load and that instrumentation capable
of detecting giant particles will be key to dust observations in
this part of the world.
Publisher
Copernicus GmbH
Subject
Atmospheric Science
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