Aerosol influences on low-level clouds in the West African monsoon
<p>Low-level clouds (LLCs) cover a wide area of southern West Africa (SWA) during the summer monsoon months and have an important cooling effect on the regional climate. Previous studies of these clouds have focused on modelling and remote sensing via satellite. We present the first comprehens...
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Copernicus Publications
2019-07-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/19/8503/2019/acp-19-8503-2019.pdf |
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| author | J. W. Taylor S. L. Haslett S. L. Haslett K. Bower M. Flynn I. Crawford J. Dorsey J. Dorsey T. Choularton P. J. Connolly V. Hahn C. Voigt C. Voigt D. Sauer R. Dupuy J. Brito J. Brito A. Schwarzenboeck T. Bourriane C. Denjean P. Rosenberg C. Flamant J. D. Lee J. D. Lee A. R. Vaughan P. G. Hill B. Brooks V. Catoire P. Knippertz H. Coe |
| author_facet | J. W. Taylor S. L. Haslett S. L. Haslett K. Bower M. Flynn I. Crawford J. Dorsey J. Dorsey T. Choularton P. J. Connolly V. Hahn C. Voigt C. Voigt D. Sauer R. Dupuy J. Brito J. Brito A. Schwarzenboeck T. Bourriane C. Denjean P. Rosenberg C. Flamant J. D. Lee J. D. Lee A. R. Vaughan P. G. Hill B. Brooks V. Catoire P. Knippertz H. Coe |
| author_sort | J. W. Taylor |
| collection | DOAJ |
| description | <p>Low-level clouds (LLCs) cover a wide area of southern West Africa (SWA) during the summer monsoon months and have an important cooling effect on the regional climate. Previous studies of these clouds have focused on modelling and remote sensing via satellite. We present the first comprehensive set of in situ measurements of cloud microphysics from the region, taken during June–July 2016, as part of the DACCIWA (Dynamics–aerosol–chemistry–cloud interactions in West Africa) campaign. This novel dataset allows us to assess spatial, diurnal, and day-to-day variation in the properties of these clouds over the region.</p>
<p>LLCs developed overnight and mean cloud cover peaked a few hundred kilometres inland around 10:00 local solar time (LST), before clouds began to dissipate and convection intensified in the afternoon. Regional variation in LLC cover was largely orographic, and no lasting impacts in cloud cover related to pollution plumes were observed downwind of major population centres.</p>
<p>The boundary layer cloud drop number concentration (CDNC) was locally variable inland, ranging from 200 to 840 <span class="inline-formula">cm<sup>−3</sup></span> (10th and 90th percentiles at standard temperature and pressure), but showed no systematic regional variations. Enhancements were seen in pollution plumes from the coastal cities but were not statistically significant across the region. A significant fraction of accumulation mode aerosols, and therefore cloud condensation nuclei, were from ubiquitous biomass burning smoke transported from the Southern Hemisphere.</p>
<p>To assess the relative importance of local and transported aerosol on the cloud field, we isolated the local contribution to the aerosol population by comparing inland and offshore size and composition measurements. A parcel model<span id="page8504"/> sensitivity analysis showed that doubling or halving local emissions only changed the calculated cloud drop number concentration by 13 %–22 %, as the high background meant local emissions were a small fraction of total aerosol. As the population of SWA grows, local emissions are expected to rise. Biomass burning smoke transported from the Southern Hemisphere is likely to dampen any effect of these increased local emissions on cloud–aerosol interactions. An integrative analysis between local pollution and Central African biomass burning emissions must be considered when predicting anthropogenic impacts on the regional cloud field during the West African summer monsoon.</p> |
| first_indexed | 2024-12-22T04:37:33Z |
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| issn | 1680-7316 1680-7324 |
| language | English |
| last_indexed | 2024-12-22T04:37:33Z |
| publishDate | 2019-07-01 |
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| series | Atmospheric Chemistry and Physics |
| spelling | doaj.art-ed6b5059b9974e198636f0318ecffcdd2022-12-21T18:38:51ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242019-07-01198503852210.5194/acp-19-8503-2019Aerosol influences on low-level clouds in the West African monsoonJ. W. Taylor0S. L. Haslett1S. L. Haslett2K. Bower3M. Flynn4I. Crawford5J. Dorsey6J. Dorsey7T. Choularton8P. J. Connolly9V. Hahn10C. Voigt11C. Voigt12D. Sauer13R. Dupuy14J. Brito15J. Brito16A. Schwarzenboeck17T. Bourriane18C. Denjean19P. Rosenberg20C. Flamant21J. D. Lee22J. D. Lee23A. R. Vaughan24P. G. Hill25B. Brooks26V. Catoire27P. Knippertz28H. Coe29Centre for Atmospheric Science, School of Earth and Environmental Sciences, University of Manchester, Manchester, UKCentre for Atmospheric Science, School of Earth and Environmental Sciences, University of Manchester, Manchester, UKnow at: Department of Environmental Science and Analytical Chemistry, Stockholm University, Stockholm 114 18, SwedenCentre for Atmospheric Science, School of Earth and Environmental Sciences, University of Manchester, Manchester, UKCentre for Atmospheric Science, School of Earth and Environmental Sciences, University of Manchester, Manchester, UKCentre for Atmospheric Science, School of Earth and Environmental Sciences, University of Manchester, Manchester, UKCentre for Atmospheric Science, School of Earth and Environmental Sciences, University of Manchester, Manchester, UKNational Centre for Atmospheric Science, University of Manchester, Manchester, UKCentre for Atmospheric Science, School of Earth and Environmental Sciences, University of Manchester, Manchester, UKCentre for Atmospheric Science, School of Earth and Environmental Sciences, University of Manchester, Manchester, UKInstitut für Physik der Atmosphäre, Deutsches Zentrum für Luft- und Raumfahrt (DLR), Oberpfaffenhofen, GermanyInstitut für Physik der Atmosphäre, Deutsches Zentrum für Luft- und Raumfahrt (DLR), Oberpfaffenhofen, GermanyInstitut für Physik der Atmosphäre, Johannes Gutenberg-Universität Mainz, Mainz, GermanyInstitut für Physik der Atmosphäre, Deutsches Zentrum für Luft- und Raumfahrt (DLR), Oberpfaffenhofen, GermanyLaboratoire de Météorologie Physique, Université Clermont Auvergne, Clermont-Ferrand, FranceLaboratoire de Météorologie Physique, Université Clermont Auvergne, Clermont-Ferrand, Francenow at: IMT Lille Douai, Université de Lille, SAGE, 59000 Lille, FranceLaboratoire de Météorologie Physique, Université Clermont Auvergne, Clermont-Ferrand, FranceCNRM, Université de Toulouse, Météo-France, CNRS, Toulouse, FranceCNRM, Université de Toulouse, Météo-France, CNRS, Toulouse, FranceSchool of Earth and Environment, University of Leeds, Leeds, UKLATMOS/IPSL, Sorbonne Université, UVSQ, CNRS, Paris, FranceWolfson Atmospheric Chemistry Laboratories, University of York, York, UKNational Centre for Atmospheric Science, University of York, York, UKWolfson Atmospheric Chemistry Laboratories, University of York, York, UKDepartment of Meteorology, University of Reading, Reading, UKNational Centre for Atmospheric Science, Leeds, UKLaboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Université Orléans-CNRS-CNES, Orléans CEDEX 2, FranceInstitute of Meteorology and Climate Research, Karlsruhe Institute of Technology, Karlsruhe, GermanyCentre for Atmospheric Science, School of Earth and Environmental Sciences, University of Manchester, Manchester, UK<p>Low-level clouds (LLCs) cover a wide area of southern West Africa (SWA) during the summer monsoon months and have an important cooling effect on the regional climate. Previous studies of these clouds have focused on modelling and remote sensing via satellite. We present the first comprehensive set of in situ measurements of cloud microphysics from the region, taken during June–July 2016, as part of the DACCIWA (Dynamics–aerosol–chemistry–cloud interactions in West Africa) campaign. This novel dataset allows us to assess spatial, diurnal, and day-to-day variation in the properties of these clouds over the region.</p> <p>LLCs developed overnight and mean cloud cover peaked a few hundred kilometres inland around 10:00 local solar time (LST), before clouds began to dissipate and convection intensified in the afternoon. Regional variation in LLC cover was largely orographic, and no lasting impacts in cloud cover related to pollution plumes were observed downwind of major population centres.</p> <p>The boundary layer cloud drop number concentration (CDNC) was locally variable inland, ranging from 200 to 840 <span class="inline-formula">cm<sup>−3</sup></span> (10th and 90th percentiles at standard temperature and pressure), but showed no systematic regional variations. Enhancements were seen in pollution plumes from the coastal cities but were not statistically significant across the region. A significant fraction of accumulation mode aerosols, and therefore cloud condensation nuclei, were from ubiquitous biomass burning smoke transported from the Southern Hemisphere.</p> <p>To assess the relative importance of local and transported aerosol on the cloud field, we isolated the local contribution to the aerosol population by comparing inland and offshore size and composition measurements. A parcel model<span id="page8504"/> sensitivity analysis showed that doubling or halving local emissions only changed the calculated cloud drop number concentration by 13 %–22 %, as the high background meant local emissions were a small fraction of total aerosol. As the population of SWA grows, local emissions are expected to rise. Biomass burning smoke transported from the Southern Hemisphere is likely to dampen any effect of these increased local emissions on cloud–aerosol interactions. An integrative analysis between local pollution and Central African biomass burning emissions must be considered when predicting anthropogenic impacts on the regional cloud field during the West African summer monsoon.</p>https://www.atmos-chem-phys.net/19/8503/2019/acp-19-8503-2019.pdf |
| spellingShingle | J. W. Taylor S. L. Haslett S. L. Haslett K. Bower M. Flynn I. Crawford J. Dorsey J. Dorsey T. Choularton P. J. Connolly V. Hahn C. Voigt C. Voigt D. Sauer R. Dupuy J. Brito J. Brito A. Schwarzenboeck T. Bourriane C. Denjean P. Rosenberg C. Flamant J. D. Lee J. D. Lee A. R. Vaughan P. G. Hill B. Brooks V. Catoire P. Knippertz H. Coe Aerosol influences on low-level clouds in the West African monsoon Atmospheric Chemistry and Physics |
| title | Aerosol influences on low-level clouds in the West African monsoon |
| title_full | Aerosol influences on low-level clouds in the West African monsoon |
| title_fullStr | Aerosol influences on low-level clouds in the West African monsoon |
| title_full_unstemmed | Aerosol influences on low-level clouds in the West African monsoon |
| title_short | Aerosol influences on low-level clouds in the West African monsoon |
| title_sort | aerosol influences on low level clouds in the west african monsoon |
| url | https://www.atmos-chem-phys.net/19/8503/2019/acp-19-8503-2019.pdf |
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