Aerosol first indirect effect of African smoke at the cloud base of marine cumulus clouds over Ascension Island, southern Atlantic Ocean
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Published:2023-05-12
Issue:9
Volume:23
Page:5373-5391
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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:
de Graaf MartinORCID, Sarna Karolina, Brown Jessica, Tenner Elma V., Schenkels Manon, Donovan David P.
Abstract
Abstract. The interactions between aerosols and clouds are among the least
understood climatic processes and were studied over Ascension Island.
A ground-based UV polarization lidar was deployed on Ascension Island, which
is located in the stratocumulus-to-cumulus transition zone of the
southeastern Atlantic Ocean, to infer cloud droplet sizes and droplet
number density near the cloud base of marine boundary layer cumulus
clouds. The aerosol–cloud interaction (ACI) due to the presence of
smoke from the African continent was determined during the monsoonal
dry season. In September 2016, a cloud droplet number density ACIN
of 0.3 ± 0.21 and a cloud effective radius
ACIr of 0.18 ± 0.06 were found, due to the presence of smoke in
and under the clouds. Smaller droplets near the cloud base makes them
more susceptible to evaporation, and smoke in the marine boundary layer
over the southeastern Atlantic Ocean will likely accelerate the
stratocumulus-to-cumulus transition. The lidar retrievals were tested
against more traditional radar–radiometer measurements and shown to be
robust and at least as accurate as the lidar–radiometer measurements.
The lidar estimates of the cloud effective radius are consistent with
previous studies of cloud base droplet sizes. The lidar has the large
advantage of retrieving both cloud and aerosol properties using a
single instrument.
Funder
Koninklijke Hollandsche Maatschappij der Wetenschappen Technische Universiteit Delft Wageningen University and Research
Publisher
Copernicus GmbH
Subject
Atmospheric Science
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