Constraining aerosol–cloud adjustments by uniting surface observations with a perturbed parameter ensemble
<p>Aerosol–cloud interactions (ACIs) are the largest source of uncertainty in inferring the magnitude of future warming consistent with the observational record. The effective radiative forcing due to ACI (ERFaci) is dominated by liquid clouds and is composed of two terms: the change in cloud...
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Copernicus Publications
2025-04-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/25/4547/2025/acp-25-4547-2025.pdf |
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| author | A. Mikkelsen D. T. McCoy T. Eidhammer A. Gettelman C. Song H. Gordon I. L. McCoy I. L. McCoy |
| author_facet | A. Mikkelsen D. T. McCoy T. Eidhammer A. Gettelman C. Song H. Gordon I. L. McCoy I. L. McCoy |
| author_sort | A. Mikkelsen |
| collection | DOAJ |
| description | <p>Aerosol–cloud interactions (ACIs) are the largest source of uncertainty in inferring the magnitude of future warming consistent with the observational record. The effective radiative forcing due to ACI (ERFaci) is dominated by liquid clouds and is composed of two terms: the change in cloud albedo due to redistributing liquid over a larger number of cloud droplets (<span class="inline-formula"><i>N</i><sub>d</sub></span>) and the change in cloud macrophysical properties due to changes in cloud microphysics. These terms are, respectively, referred to as the radiative forcing due to ACI (RFaci) and aerosol–cloud adjustments. While the magnitude of RFaci is uncertain, its sign is confidently negative and results in a cooling in the historical record. In contrast, the adjustment of cloud liquid water path (LWP) to enhanced <span class="inline-formula"><i>N</i><sub>d</sub></span> and associated radiative forcing is uncertain in sign. Increased LWP in response to increased <span class="inline-formula"><i>N</i><sub>d</sub></span> is consistent with precipitation suppression, while decreased LWP in response to increased <span class="inline-formula"><i>N</i><sub>d</sub></span> is consistent with enhanced evaporation from cloud top. Observational constraints of these processes are poor in part because of causal ambiguity in the relationship between <span class="inline-formula"><i>N</i><sub>d</sub></span> and LWP. To better understand this relationship, precipitation (<span class="inline-formula"><i>P</i></span>), <span class="inline-formula"><i>N</i><sub>d</sub></span>, and LWP surface observations from the Eastern North Atlantic (ENA) atmospheric observatory are combined with the output from a perturbed parameter ensemble (PPE) hosted in the Community Atmosphere Model version 6 (CAM6). This allows for causal interpretation of observed covariability. Observations of precipitation and cloud from ENA constrain the range of possible LWP aerosol–cloud adjustments relative to the prior from the PPE by 15 %, resulting in a global value that is confidently positive (a historical cooling) ranging from 2.1 to 6.9 g m<span class="inline-formula"><sup>−2</sup></span>. It is found that observed covariability between <span class="inline-formula"><i>N</i><sub>d</sub></span> and LWP is dominated by coalescence scavenging and that this observed covariability is not strongly related to aerosol–cloud adjustments.</p> |
| format | Article |
| id | doaj-art-6c1babfef6f74f13b4d57732ecd9dd02 |
| institution | OA Journals |
| issn | 1680-7316 1680-7324 |
| language | English |
| publishDate | 2025-04-01 |
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| spelling | doaj-art-6c1babfef6f74f13b4d57732ecd9dd022025-08-20T02:18:35ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242025-04-01254547457010.5194/acp-25-4547-2025Constraining aerosol–cloud adjustments by uniting surface observations with a perturbed parameter ensembleA. Mikkelsen0D. T. McCoy1T. Eidhammer2A. Gettelman3C. Song4H. Gordon5I. L. McCoy6I. L. McCoy7Department of Atmospheric Science, University of Wyoming, Laramie, WY, USADepartment of Atmospheric Science, University of Wyoming, Laramie, WY, USANSF National Center for Atmospheric Research, Boulder, CO, USAPacific Northwest National Laboratory, Richland, WA, USADepartment of Atmospheric Science, University of Wyoming, Laramie, WY, USADepartment of Chemical Engineering and Center for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, PA, USACooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, CO, USANOAA Chemical Sciences Laboratory, Boulder, CO, USA<p>Aerosol–cloud interactions (ACIs) are the largest source of uncertainty in inferring the magnitude of future warming consistent with the observational record. The effective radiative forcing due to ACI (ERFaci) is dominated by liquid clouds and is composed of two terms: the change in cloud albedo due to redistributing liquid over a larger number of cloud droplets (<span class="inline-formula"><i>N</i><sub>d</sub></span>) and the change in cloud macrophysical properties due to changes in cloud microphysics. These terms are, respectively, referred to as the radiative forcing due to ACI (RFaci) and aerosol–cloud adjustments. While the magnitude of RFaci is uncertain, its sign is confidently negative and results in a cooling in the historical record. In contrast, the adjustment of cloud liquid water path (LWP) to enhanced <span class="inline-formula"><i>N</i><sub>d</sub></span> and associated radiative forcing is uncertain in sign. Increased LWP in response to increased <span class="inline-formula"><i>N</i><sub>d</sub></span> is consistent with precipitation suppression, while decreased LWP in response to increased <span class="inline-formula"><i>N</i><sub>d</sub></span> is consistent with enhanced evaporation from cloud top. Observational constraints of these processes are poor in part because of causal ambiguity in the relationship between <span class="inline-formula"><i>N</i><sub>d</sub></span> and LWP. To better understand this relationship, precipitation (<span class="inline-formula"><i>P</i></span>), <span class="inline-formula"><i>N</i><sub>d</sub></span>, and LWP surface observations from the Eastern North Atlantic (ENA) atmospheric observatory are combined with the output from a perturbed parameter ensemble (PPE) hosted in the Community Atmosphere Model version 6 (CAM6). This allows for causal interpretation of observed covariability. Observations of precipitation and cloud from ENA constrain the range of possible LWP aerosol–cloud adjustments relative to the prior from the PPE by 15 %, resulting in a global value that is confidently positive (a historical cooling) ranging from 2.1 to 6.9 g m<span class="inline-formula"><sup>−2</sup></span>. It is found that observed covariability between <span class="inline-formula"><i>N</i><sub>d</sub></span> and LWP is dominated by coalescence scavenging and that this observed covariability is not strongly related to aerosol–cloud adjustments.</p>https://acp.copernicus.org/articles/25/4547/2025/acp-25-4547-2025.pdf |
| spellingShingle | A. Mikkelsen D. T. McCoy T. Eidhammer A. Gettelman C. Song H. Gordon I. L. McCoy I. L. McCoy Constraining aerosol–cloud adjustments by uniting surface observations with a perturbed parameter ensemble Atmospheric Chemistry and Physics |
| title | Constraining aerosol–cloud adjustments by uniting surface observations with a perturbed parameter ensemble |
| title_full | Constraining aerosol–cloud adjustments by uniting surface observations with a perturbed parameter ensemble |
| title_fullStr | Constraining aerosol–cloud adjustments by uniting surface observations with a perturbed parameter ensemble |
| title_full_unstemmed | Constraining aerosol–cloud adjustments by uniting surface observations with a perturbed parameter ensemble |
| title_short | Constraining aerosol–cloud adjustments by uniting surface observations with a perturbed parameter ensemble |
| title_sort | constraining aerosol cloud adjustments by uniting surface observations with a perturbed parameter ensemble |
| url | https://acp.copernicus.org/articles/25/4547/2025/acp-25-4547-2025.pdf |
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