Effects of marine organic aerosols as sources of immersion-mode ice-nucleating particles on high-latitude mixed-phase clouds
<p>Mixed-phase clouds are frequently observed in high-latitude regions and have important impacts on the surface energy budget and regional climate. Marine organic aerosol (MOA), a natural source of aerosol emitted over <span class="inline-formula">∼</span> 70 % of Earth&...
Main Authors: | , , , |
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Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2021-02-01
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Series: | Atmospheric Chemistry and Physics |
Online Access: | https://acp.copernicus.org/articles/21/2305/2021/acp-21-2305-2021.pdf |
Summary: | <p>Mixed-phase clouds are frequently observed in high-latitude regions and have important impacts on the surface energy budget
and regional climate. Marine organic aerosol (MOA), a natural source of
aerosol emitted over <span class="inline-formula">∼</span> 70 % of Earth's surface, may
significantly modify the properties and radiative forcing of mixed-phase
clouds. However, the relative importance of MOA as a source of ice-nucleating particles (INPs) in comparison to mineral dust, and MOA's effects
as cloud condensation nuclei (CCN) and INPs on mixed-phase clouds are still
open questions. In this study, we implement MOA as a new aerosol species
into the Community Atmosphere Model version 6 (CAM6), the atmosphere
component of the Community Earth System Model version 2 (CESM2), and allow
the treatment of aerosol–cloud interactions of MOA via droplet activation
and ice nucleation. CAM6 reproduces observed seasonal cycles of marine
organic matter at Mace Head and Amsterdam Island when the MOA fraction of
sea spray aerosol in the model is assumed to depend on sea spray biology
but fails when this fraction is assumed to be constant. Model results
indicate that marine INPs dominate primary ice nucleation below 400 hPa over
the Southern Ocean and Arctic boundary layer, while dust INPs are more
abundant elsewhere. By acting as CCN, MOA exerts a shortwave cloud forcing
change of <span class="inline-formula">−</span>2.78 W m<span class="inline-formula"><sup>−2</sup></span> over the Southern Ocean in the austral summer.
By acting as INPs, MOA enhances the longwave cloud forcing by 0.35 W m<span class="inline-formula"><sup>−2</sup></span> over the Southern Ocean in the austral winter. The annual global
mean net cloud forcing changes due to CCN and INPs of MOA are <span class="inline-formula">−</span>0.35 and
0.016 W m<span class="inline-formula"><sup>−2</sup></span>, respectively. These findings highlight the vital
importance for Earth system models to consider MOA as an important
aerosol species for the interactions of biogeochemistry, hydrological cycle,
and climate change.</p> |
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ISSN: | 1680-7316 1680-7324 |