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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Preprints
https://doi.org/10.5194/acp-2019-1085
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2019-1085
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

  04 Dec 2019

04 Dec 2019

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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.

The value of remote marine aerosol measurements for constraining radiative forcing uncertainty

Leighton A. Regayre1, Julia Schmale2, Jill S. Johnson1, Christian Tatzelt3, Andrea Baccarini2, Silvia Henning3, Masaru Yoshioka1, Frank Stratmann3, Martin Gysel-Beer2, and Ken S. Carslaw1 Leighton A. Regayre et al.
  • 1Institute for Climate and Atmospheric Science, School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK
  • 2Paul Scherrer Institute, Laboratory of Atmospheric Chemistry, Villigen, Switzerland
  • 3Leibniz Institute forTropospheric Research, Leipzig, Germany

Abstract. Aerosol measurements over the Southern Ocean are used to constrain aerosol-cloud interaction radiative forcing uncertainty in a global climate model. Aerosol forcing uncertainty is quantified using one million climate model variants that sample the uncertainty in nearly 30 model parameters. Ship-based measurements of cloud condensation nuclei, particle number concentrations and sulfate mass concentrations from the Antarctic Circumnavigation Expedition: Study of Preindustrial-like Aerosols and Their Climate Effects (ACE-SPACE) are used to identify observationally implausible variants and thereby reduce the spread in the simulated forcing. Southern Ocean measurements strongly constrain natural aerosol emissions: default sea spray emissions in the model need to be increased by around a factor of 3 to be consistent with measurements. Aerosol forcing uncertainty is reduced by around 7 % using these measurements, which is comparable to the 8 % reduction achieved using an extensive set of over 9000 predominantly Northern Hemisphere measurements. The radiative forcing due to aerosol–cloud interactions (RFaci) is constrained to −2.61 to −1.10 W m−2 (95 % confidence) and the effective radiative forcing from aerosol-cloud interactions (ERFaci) is constrained to −2.43 to −0.54 W m−2. When Southern Ocean and Northern Hemisphere measurements are combined, the uncertainty in RFaci is reduced by 21 % and the strongest 20 % of forcing values are ruled out as implausible. In this combined constraint the observationally plausible RFaci is around 0.17 W m−2 weaker (less negative) with credible values ranging from −2.51 to −1.17 W m−2 and from −2.18 to −1.46 W m−2 when using one standard deviation to quantify the uncertainty. The Southern Ocean and Northern Hemisphere measurement datasets are complementary because they constrain different processes. These results highlight the value of remote marine aerosol measurements.

Leighton A. Regayre et al.

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Leighton A. Regayre et al.

Leighton A. Regayre et al.

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Latest update: 11 Aug 2020
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Short summary
The amount of energy reflected back into space because of man-made particles is highly uncertain. Processes related to naturally occurring particles cause most of the uncertainty, but these processes are poorly constrained by present-day measurements. We show that measurements over the Southern Ocean, far from pollution sources, efficiently reduce climate model uncertainties. Our results pave the way to designing experiments and measurement campaigns that reduce this uncertainty even further.
The amount of energy reflected back into space because of man-made particles is highly...
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