@article{Quaas:2020:10.5194/acp-20-15079-2020,
author = {Quaas, J and Arola, A and Cairns, B and Christensen, M and Deneke, H and Ekman, AML and Feingold, G and Fridlind, A and Gryspeerdt, E and Hasekamp, O and Li, Z and Lipponen, A and Ma, P-L and Mülmenstädt, J and Nenes, A and Penner, J and Rosenfeld, D and Schrödner, R and Sinclair, K and Sourdeval, O and Stier, P and Tesche, M and van, Diedenhoven B and Wendisch, M},
doi = {10.5194/acp-20-15079-2020},
journal = {Atmospheric Chemistry and Physics},
pages = {15079--15099},
title = {Constraining the Twomey effect from satellite observations: Issues and perspectives},
url = {http://dx.doi.org/10.5194/acp-20-15079-2020},
volume = {20},
year = {2020}
}

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TY  - JOUR
AB  - The Twomey effect describes the radiative forcing associated with a change in cloud albedo due to an increase in anthropogenic aerosol emissions. It is driven by the perturbation in cloud droplet number concentration (ΔNd, ant) in liquid-water clouds and is currently understood to exert a cooling effect on climate. The Twomey effect is the key driver in the effective radiative forcing due to aerosol–cloud interactions, but rapid adjustments also contribute. These adjustments are essentially the responses of cloud fraction and liquid water path to ΔNd, ant and thus scale approximately with it. While the fundamental physics of the influence of added aerosol particles on the droplet concentration (Nd) is well described by established theory at the particle scale (micrometres), how this relationship is expressed at the large-scale (hundreds of kilometres) perturbation, ΔNd, ant, remains uncertain. The discrepancy between process understanding at particle scale and insufficient quantification at the climate-relevant large scale is caused by co-variability of aerosol particles and updraught velocity and by droplet sink processes. These operate at scales on the order of tens of metres at which only localised observations are available and at which no approach yet exists to quantify the anthropogenic perturbation. Different atmospheric models suggest diverse magnitudes of the Twomey effect even when applying the same anthropogenic aerosol emission perturbation. Thus, observational data are needed to quantify and constrain the Twomey effect. At the global scale, this means satellite data. There are four key uncertainties in determining ΔNd, ant, namely the quantification of (i) the cloud-active aerosol – the cloud condensation nuclei (CCN) concentrations at or above cloud base, (ii) Nd, (iii) the statistical approach for inferring the sensitivity of Nd to aerosol particles from the satellite data and (iv) uncert
AU  - Quaas,J
AU  - Arola,A
AU  - Cairns,B
AU  - Christensen,M
AU  - Deneke,H
AU  - Ekman,AML
AU  - Feingold,G
AU  - Fridlind,A
AU  - Gryspeerdt,E
AU  - Hasekamp,O
AU  - Li,Z
AU  - Lipponen,A
AU  - Ma,P-L
AU  - Mülmenstädt,J
AU  - Nenes,A
AU  - Penner,J
AU  - Rosenfeld,D
AU  - Schrödner,R
AU  - Sinclair,K
AU  - Sourdeval,O
AU  - Stier,P
AU  - Tesche,M
AU  - van,Diedenhoven B
AU  - Wendisch,M
DO  - 10.5194/acp-20-15079-2020
EP  - 15099
PY  - 2020///
SN  - 1680-7316
SP  - 15079
TI  - Constraining the Twomey effect from satellite observations: Issues and perspectives
T2  - Atmospheric Chemistry and Physics
UR  - http://dx.doi.org/10.5194/acp-20-15079-2020
UR  - http://hdl.handle.net/10044/1/84738
VL  - 20
ER  - 

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