Cloud, precipitation and radiation responses to large perturbations in global dimethyl sulfide
<p>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 poo...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-07-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/18/10177/2018/acp-18-10177-2018.pdf |
| Summary: | <p>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 −1.4 W m<sup>−2</sup>
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∕ − 5 W m<sup>−2</sup>) 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
0.019 K per Tg yr<sup>−1</sup> 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.</p> |
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| ISSN: | 1680-7316 1680-7324 |