Models transport Saharan dust too low in the atmosphere: a comparison of the MetUM and CAMS forecasts with observations
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Published:2020-11-05
Issue:21
Volume:20
Page:12955-12982
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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:
O'Sullivan Debbie, Marenco FrancoORCID, Ryder Claire L.ORCID, Pradhan YaswantORCID, Kipling ZakORCID, Johnson BenORCID, Benedetti AngelaORCID, Brooks MelissaORCID, McGill Matthew, Yorks John, Selmer Patrick
Abstract
Abstract. We investigate the dust forecasts from two operational global
atmospheric models in comparison with in situ and remote sensing
measurements obtained during the AERosol properties – Dust (AER-D) field
campaign. Airborne elastic backscatter lidar measurements were performed
on board the Facility for Airborne Atmospheric Measurements during August
2015 over the eastern Atlantic, and they permitted us to characterise the dust
vertical distribution in detail, offering insights on transport from the
Sahara. They were complemented with airborne in situ measurements of dust
size distribution and optical properties, as well as datasets from the
Cloud–Aerosol Transport System (CATS) spaceborne lidar and the Moderate
Resolution Imaging Spectroradiometer (MODIS). We compare the airborne and
spaceborne datasets to operational predictions obtained from the Met Office
Unified Model (MetUM) and the Copernicus Atmosphere Monitoring Service
(CAMS). The dust aerosol optical depth predictions from the models are
generally in agreement with the observations but display a low bias.
However, the predicted vertical distribution places the dust lower in the
atmosphere than highlighted in our observations. This is particularly
noticeable for the MetUM, which does not transport coarse dust high enough
in the atmosphere or far enough away from the source. We also found that both
model forecasts underpredict coarse-mode dust and at times overpredict fine-mode dust, but as they are fine-tuned to represent the observed optical
depth, the fine mode is set to compensate for the underestimation of the
coarse mode. As aerosol–cloud interactions are dependent on particle numbers
rather than on the optical properties, this behaviour is likely to affect
their correct representation. This leads us to propose an augmentation of
the set of aerosol observations available on a global scale for constraining
models, with a better focus on the vertical distribution and on the particle
size distribution. Mineral dust is a major component of the climate system;
therefore, it is important to work towards improving how models reproduce its
properties and transport mechanisms.
Publisher
Copernicus GmbH
Subject
Atmospheric Science
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