Drivers of cloud droplet number variability in the summertime in the southeastern United States
<p>Here we analyze regional-scale data collected on board the NOAA WP-3D aircraft during the 2013 Southeast Nexus (SENEX) campaign to study the aerosol–cloud droplet link and quantify the sensitivity of droplet number to aerosol number, chemical composition, and vertical velocity. For this, th...
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Language: | English |
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Copernicus Publications
2020-10-01
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Series: | Atmospheric Chemistry and Physics |
Online Access: | https://acp.copernicus.org/articles/20/12163/2020/acp-20-12163-2020.pdf |
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doaj-189d8510f6b84ad5a0b52761fba602e9 |
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record_format |
Article |
collection |
DOAJ |
language |
English |
format |
Article |
sources |
DOAJ |
author |
A. Bougiatioti A. Bougiatioti A. Nenes A. Nenes A. Nenes J. J. Lin J. J. Lin C. A. Brock J. A. de Gouw J. A. de Gouw J. A. de Gouw J. Liao J. Liao J. Liao J. Liao A. M. Middlebrook A. Welti A. Welti A. Welti |
spellingShingle |
A. Bougiatioti A. Bougiatioti A. Nenes A. Nenes A. Nenes J. J. Lin J. J. Lin C. A. Brock J. A. de Gouw J. A. de Gouw J. A. de Gouw J. Liao J. Liao J. Liao J. Liao A. M. Middlebrook A. Welti A. Welti A. Welti Drivers of cloud droplet number variability in the summertime in the southeastern United States Atmospheric Chemistry and Physics |
author_facet |
A. Bougiatioti A. Bougiatioti A. Nenes A. Nenes A. Nenes J. J. Lin J. J. Lin C. A. Brock J. A. de Gouw J. A. de Gouw J. A. de Gouw J. Liao J. Liao J. Liao J. Liao A. M. Middlebrook A. Welti A. Welti A. Welti |
author_sort |
A. Bougiatioti |
title |
Drivers of cloud droplet number variability in the summertime in the southeastern United States |
title_short |
Drivers of cloud droplet number variability in the summertime in the southeastern United States |
title_full |
Drivers of cloud droplet number variability in the summertime in the southeastern United States |
title_fullStr |
Drivers of cloud droplet number variability in the summertime in the southeastern United States |
title_full_unstemmed |
Drivers of cloud droplet number variability in the summertime in the southeastern United States |
title_sort |
drivers of cloud droplet number variability in the summertime in the southeastern united states |
publisher |
Copernicus Publications |
series |
Atmospheric Chemistry and Physics |
issn |
1680-7316 1680-7324 |
publishDate |
2020-10-01 |
description |
<p>Here we analyze regional-scale data collected on board the NOAA WP-3D aircraft during the 2013
Southeast Nexus (SENEX) campaign to study the aerosol–cloud droplet link and quantify the
sensitivity of droplet number to aerosol number, chemical composition, and vertical velocity. For
this, the observed aerosol size distributions, chemical composition, and vertical-velocity
distribution are introduced into a state-of-the-art cloud droplet parameterization to show that
cloud maximum supersaturations in the region range from 0.02 % to 0.52 %, with
an average of <span class="inline-formula">0.14±0.05</span> %. Based on these low values of supersaturation, the
majority of activated droplets correspond to particles with a dry diameter of 90 <span class="inline-formula">nm</span> and above.
An important finding is that the standard deviation of the vertical velocity
(<span class="inline-formula"><i>σ</i><sub>w</sub></span>) exhibits considerable diurnal variability (ranging from
0.16 <span class="inline-formula">m s<sup>−1</sup></span> during nighttime to over 1.2 <span class="inline-formula">m s<sup>−1</sup></span> during day), and it tends to
covary with total aerosol number (<span class="inline-formula"><i>N</i><sub>a</sub></span>). This <span class="inline-formula"><i>σ</i><sub>w</sub></span>–<span class="inline-formula"><i>N</i><sub>a</sub></span>
covariance amplifies the predicted response in cloud droplet number (<span class="inline-formula"><i>N</i><sub>d</sub></span>) to
<span class="inline-formula"><i>N</i><sub>a</sub></span> increases by 3 to 5 times compared to expectations based on <span class="inline-formula"><i>N</i><sub>a</sub></span>
changes alone. This amplified response is important given that droplet formation is often
velocity-limited and therefore should normally be insensitive to aerosol changes. We also find
that <span class="inline-formula"><i>N</i><sub>d</sub></span> cannot exceed a characteristic concentration that depends solely on
<span class="inline-formula"><i>σ</i><sub>w</sub></span>. Correct consideration of <span class="inline-formula"><i>σ</i><sub>w</sub></span> and its covariance with time
and <span class="inline-formula"><i>N</i><sub>a</sub></span> is important for fully understanding aerosol–cloud interactions and the
magnitude of the aerosol indirect effect. Given that model assessments of aerosol–cloud–climate
interactions do not routinely evaluate for overall turbulence or its covariance with other
parameters, datasets and analyses such as the one presented here are of the highest priority to
address unresolved sources of hydrometeor variability, bias, and the response of droplet number to
aerosol perturbations.</p> |
url |
https://acp.copernicus.org/articles/20/12163/2020/acp-20-12163-2020.pdf |
work_keys_str_mv |
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spelling |
doaj-189d8510f6b84ad5a0b52761fba602e92020-11-25T03:36:37ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242020-10-0120121631217610.5194/acp-20-12163-2020Drivers of cloud droplet number variability in the summertime in the southeastern United StatesA. Bougiatioti0A. Bougiatioti1A. Nenes2A. Nenes3A. Nenes4J. J. Lin5J. J. Lin6C. A. Brock7J. A. de Gouw8J. A. de Gouw9J. A. de Gouw10J. Liao11J. Liao12J. Liao13J. Liao14A. M. Middlebrook15A. Welti16A. Welti17A. Welti18Institute for Environmental Research and Sustainable Development, National Observatory of Athens, P. Penteli, 15236, GreeceSchool of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332, USASchool of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332, USALaboratory of Atmospheric Processes and their Impacts, School of Architecture, Civil and Environmental Engineering, École Polytechnique Fédérale de Lausanne, 1015 Lausanne, SwitzerlandInstitute for Chemical Engineering Sciences, Foundation for Research and Technology Hellas, 26504 Patras, GreeceSchool of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332, USAnow at: Nano and Molecular Systems Research Unit, University of Oulu, 90014 Oulu, FinlandChemical Sciences Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO 80305, USAChemical Sciences Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO 80305, USACooperative Institute for Research in Environmental Sciences, Univ. of Colorado, Boulder, CO 80309, USAnow at: Department of Chemistry and Biochemistry, University of Colorado Boulder, Boulder, CO 80309, USAChemical Sciences Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO 80305, USACooperative Institute for Research in Environmental Sciences, Univ. of Colorado, Boulder, CO 80309, USAnow at: Atmospheric Chemistry and Dynamic Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USAnow at: Universities Space Research Association, GESTAR, Columbia, MD 21046, USAChemical Sciences Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO 80305, USAChemical Sciences Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO 80305, USACooperative Institute for Research in Environmental Sciences, Univ. of Colorado, Boulder, CO 80309, USAnow at: Atmospheric Composition Research Unit, Finnish Meteorological Institute, 00560 Helsinki, Finland<p>Here we analyze regional-scale data collected on board the NOAA WP-3D aircraft during the 2013 Southeast Nexus (SENEX) campaign to study the aerosol–cloud droplet link and quantify the sensitivity of droplet number to aerosol number, chemical composition, and vertical velocity. For this, the observed aerosol size distributions, chemical composition, and vertical-velocity distribution are introduced into a state-of-the-art cloud droplet parameterization to show that cloud maximum supersaturations in the region range from 0.02 % to 0.52 %, with an average of <span class="inline-formula">0.14±0.05</span> %. Based on these low values of supersaturation, the majority of activated droplets correspond to particles with a dry diameter of 90 <span class="inline-formula">nm</span> and above. An important finding is that the standard deviation of the vertical velocity (<span class="inline-formula"><i>σ</i><sub>w</sub></span>) exhibits considerable diurnal variability (ranging from 0.16 <span class="inline-formula">m s<sup>−1</sup></span> during nighttime to over 1.2 <span class="inline-formula">m s<sup>−1</sup></span> during day), and it tends to covary with total aerosol number (<span class="inline-formula"><i>N</i><sub>a</sub></span>). This <span class="inline-formula"><i>σ</i><sub>w</sub></span>–<span class="inline-formula"><i>N</i><sub>a</sub></span> covariance amplifies the predicted response in cloud droplet number (<span class="inline-formula"><i>N</i><sub>d</sub></span>) to <span class="inline-formula"><i>N</i><sub>a</sub></span> increases by 3 to 5 times compared to expectations based on <span class="inline-formula"><i>N</i><sub>a</sub></span> changes alone. This amplified response is important given that droplet formation is often velocity-limited and therefore should normally be insensitive to aerosol changes. We also find that <span class="inline-formula"><i>N</i><sub>d</sub></span> cannot exceed a characteristic concentration that depends solely on <span class="inline-formula"><i>σ</i><sub>w</sub></span>. Correct consideration of <span class="inline-formula"><i>σ</i><sub>w</sub></span> and its covariance with time and <span class="inline-formula"><i>N</i><sub>a</sub></span> is important for fully understanding aerosol–cloud interactions and the magnitude of the aerosol indirect effect. Given that model assessments of aerosol–cloud–climate interactions do not routinely evaluate for overall turbulence or its covariance with other parameters, datasets and analyses such as the one presented here are of the highest priority to address unresolved sources of hydrometeor variability, bias, and the response of droplet number to aerosol perturbations.</p>https://acp.copernicus.org/articles/20/12163/2020/acp-20-12163-2020.pdf |