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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/acp-2020-57
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2020-57
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  16 Apr 2020

16 Apr 2020

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A revised version of this preprint was accepted for the journal ACP and is expected to appear here in due course.

Models transport Saharan dust too low in the atmosphere compared to observations

Debbie O'Sullivan1, Franco Marenco1, Claire L. Ryder2, Yaswant Pradhan1, Zak Kipling3, Ben Johnson1, Angela Benedetti3, Melissa Brooks1, Matthew McGill4, John Yorks4, and Patrick Selmer4 Debbie O'Sullivan et al.
  • 1Met Office, Exeter, EX1 3PB, UK
  • 2Department of Meteorology, University of Reading, RG6 6BB, UK
  • 3European Centre for Medium-Range Weather Forecasts, Reading, RG2 9AX, UK
  • 4NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA

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 to characterize 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, and datasets from the Cloud-Aerosol Transport System spaceborne lidar (CATS) 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, nor far enough away from source. We also found that both model forecasts underpredict coarse mode dust, and at times overpredict fine mode dust. An analysis of the processes driving dust uplift in the models suggests that errors in the large scale wind and dust size distribution at source could be the cause of differences between model predictions and observations of the Saharan Air Layer. Mineral dust is an important component of the climate system, therefore it is important to assess how models reproduce its properties and transport mechanisms.

Debbie O'Sullivan et al.

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Debbie O'Sullivan et al.

Debbie O'Sullivan et al.

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Latest update: 26 Oct 2020
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Short summary
Mineral dust is an important component of the climate system, and we assess how well it is predicted by two operational models. We have flown an aircraft in the dust layers in the Eastern Atlantic, and we also make use of satellites. We show that models predict the dust layer too low and that it predicts the particles to be too small. We believe that these discrepancies may be overcome if models can be constrained with better observations of the dust vertical and size-resolved distribution.
Mineral dust is an important component of the climate system, and we assess how well it is...
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