Time-dependent entrainment of smoke presents an observational challenge for assessing aerosol–cloud interactions over the southeast Atlantic Ocean
The colocation of clouds and smoke over the southeast Atlantic Ocean during the southern African biomass burning season has numerous radiative implications, including microphysical modulation of the clouds if smoke is entrained into the marine boundary layer. NASA's ObseRvations of Aerosols abo...
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Published in | Atmospheric chemistry and physics Vol. 18; no. 19; pp. 14623 - 14636 |
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Main Authors | , , , , , , , , , |
Format | Journal Article |
Language | English |
Published |
Katlenburg-Lindau
Copernicus GmbH
12.10.2018
Copernicus Publications |
Subjects | |
Online Access | Get full text |
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Summary: | The colocation of clouds and smoke over the southeast Atlantic
Ocean during the southern African biomass burning season has numerous
radiative implications, including microphysical modulation of the clouds if
smoke is entrained into the marine boundary layer. NASA's ObseRvations of
Aerosols above CLouds and their intEractionS (ORACLES) campaign is studying
this system with aircraft in three field deployments between 2016 and 2018.
Results from ORACLES-2016 show that the relationship between cloud droplet
number concentration and smoke below cloud is consistent with previously
reported values, whereas cloud droplet number concentration is only weakly
associated with smoke immediately above cloud at the time of observation.
By combining field observations, regional chemistry–climate modeling, and
theoretical boundary layer aerosol budget equations, we show that the history
of smoke entrainment (which has a characteristic mixing timescale on the
order of days) helps explain variations in cloud properties for similar
instantaneous above-cloud smoke environments. Precipitation processes can
obscure the relationship between above-cloud smoke and cloud properties in
parts of the southeast Atlantic, but marine boundary layer carbon monoxide
concentrations for two case study flights suggest that smoke entrainment
history drove the observed differences in cloud properties for those days. A
Lagrangian framework following the clouds and accounting for the history of
smoke entrainment and precipitation is likely necessary for quantitatively
studying this system; an Eulerian framework (e.g., instantaneous correlation
of A-train satellite observations) is unlikely to capture the true extent of
smoke–cloud interaction in the southeast Atlantic. |
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ISSN: | 1680-7324 1680-7316 1680-7324 |
DOI: | 10.5194/acp-18-14623-2018 |