Nd or not Nd? To what extent are biomass burning aerosols modulating cloud microphysics in the southeast Atlantic?

Abstract

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. The ORACLES campaign is deploying aircraft to study this system in three field deployments between 2016 and 2018. Results from ORACLES-2016 show that cloud droplet number concentration is generally correlated with smoke below cloud but weakly associated with smoke immediately above cloud at the time of observation. Combining field observations and regional chemistry-climate modeling, we show that the history of entrainment (characteristic timescale of ~3 days) can explain variation in cloud properties for similar above-cloud smoke environments. A Lagrangian framework following the clouds and accounting for the history of smoke entrainment is necessary for studying this system: an Eulerian framework (e.g., A-train satellite observation correlation) cannot capture the true extent of smoke-cloud interaction.