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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 18, issue 14 | Copyright
Atmos. Chem. Phys., 18, 10177-10198, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 17 Jul 2018

Research article | 17 Jul 2018

Cloud, precipitation and radiation responses to large perturbations in global dimethyl sulfide

Sonya L. Fiddes1,2,3, Matthew T. Woodhouse3, Zebedee Nicholls1, Todd P. Lane4, and Robyn Schofield2 Sonya L. Fiddes et al.
  • 1Australian–German Climate and Energy College, University of Melbourne, Parkville, 3010, Australia
  • 2ARC Centre of Excellence for Climate System Science, School of Earth Sciences, University of Melbourne, Parkville, 3010, Australia
  • 3Climate Science Centre, Oceans and Atmosphere, Commonwealth Scientific and Industrial Research Organisation, Aspendale, 3195, Australia
  • 4ARC Centre of Excellence for Climate Extremes, School of Earth Sciences, University of Melbourne, Parkville, 3010, Australia

Abstract. Natural aerosol emission represents one of the largest uncertainties in our understanding of the radiation budget. Sulfur emitted by marine organisms, as dimethyl sulfide (DMS), constitutes one-fifth of the global sulfur budget and yet the distribution, fluxes and fate of DMS remain poorly constrained. This study evaluates the Australian Community Climate and Earth System Simulator (ACCESS) United Kingdom Chemistry and Aerosol (UKCA) model in terms of cloud fraction, radiation and precipitation, and then quantifies the role of DMS in the chemistry–climate system. We find that ACCESS-UKCA has similar cloud and radiation biases to other global climate models. By removing all DMS, or alternatively significantly enhancing marine DMS, we find a top of the atmosphere radiative effect of 1.7 and −1.4W m−2 respectively. The largest responses to these DMS perturbations (removal/enhancement) are in stratiform cloud decks in the Southern Hemisphere's eastern ocean basins. These regions show significant differences in low cloud (−9∕ + 6%), surface incoming shortwave radiation (+7∕ − 5W m−2) and large-scale rainfall (+15∕ − 10%). We demonstrate a precipitation suppression effect of DMS-derived aerosol in stratiform cloud deck regions due to DMS, coupled with an increase in low cloud fraction. The difference in low cloud fraction is an example of the aerosol lifetime effect. Globally, we find a sensitivity of temperature to annual DMS flux of 0.027 and 0.019K per Tg yr−1 of sulfur, respectively. Other areas of low cloud formation, such as the Southern Ocean and stratiform cloud decks in the Northern Hemisphere, have a relatively weak response to DMS perturbations. We highlight the need for greater understanding of the DMS–climate cycle within the context of uncertainties and biases of climate models as well as those of DMS–climate observations.

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The role of natural aerosol in the climate system is uncertain. A key contributor to marine aerosol is dimethyl sulfide (DMS), released by phytoplankton in the oceans. We study the effect of DMS on clouds and rain using a climate model with a detailed aerosol scheme. We show that DMS acts to reduce rainfall in cloud deck regions, leading to longer lived clouds and a large impact on solar energy reaching the surface. Further study of these areas will improve future climate projections.
The role of natural aerosol in the climate system is uncertain. A key contributor to marine...