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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-2020-420
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2020-420
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  08 Jun 2020

08 Jun 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.

Radiative effects of long-range-transported Saharan air layers as determined from airborne lidar measurements

Manuel Gutleben1, Silke Groß1, Martin Wirth1, and Bernhard Mayer2 Manuel Gutleben et al.
  • 1Deutsches Zentrum für Luft- und Raumfahrt, Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany
  • 2Ludwig-Maximilians-University (LMU), Meteorological Institute, Munich, Germany

Abstract. The radiative effect of long-range-transported Saharan air layers is investigated on the basis of simultaneous airborne high spectral resolution and differential absorption lidar measurements in the vicinity of Barbados. Within the observed Saharan air layers increased water vapor concentrations compared to the dry trade wind atmosphere are found. The measured profiles of aerosol optical properties and water vapor mixing ratios are used to characterize the atmospheric composition in radiative transfer calculations, to calculate radiative effects of moist Saharan air layers and to determine radiative heating rate profiles. An analysis based on three case studies reveals that the observed enhanced amounts of water vapor within Saharan air layers have a much stronger impact on heating rate calculations than mineral dust aerosol. Maximum mineral dust short-wave heating and long-wave cooling rates are found in altitudes of highest dust concentration (short-wave: +0.5 Kd−1, long-wave: −0.2 Kd−1, net: +0.3 Kd−1). However, when considering both aerosol concentrations and measured water vapor mixing ratios in radiative transfer calculations the maximum heating/cooling rates shift to the top of the dust layer (short-wave: +2.2 Kd Kd−1, long-wave: −6.0 to −7.0 Kd−1, net: −5.0 to −4.0 Kd−1). Additionally, the net-heating rates decrease with height – indicating a destabilizing effect in the dust layers. Long-wave counter radiation of Saharan air layers is found to reduce cooling at the top of the subjacent marine boundary layers and might lead to less convective mixing in these layers. The overall short-wave radiative effect of mineral dust particles in Saharan air layers indicates a maximum magnitude of −40 Wm−2 at surface level and a maximum of −25 Wm−2 at the top of the atmosphere.

Manuel Gutleben et al.

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Manuel Gutleben et al.

Manuel Gutleben et al.

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Latest update: 20 Oct 2020
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Short summary
Airborne lidar measurements in the vicinity of Barbados are used to investigate radiative effects of long-range-transported Saharan air layers. Derived atmospheric heating rates indicate that observed enhanced water vapor concentrations inside these layers are the main drivers for dust vertical mixing inside the layers. Additionally, they may play a major role for the suppression of subjacent convective cloud development.
Airborne lidar measurements in the vicinity of Barbados are used to investigate radiative...
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