Publication Abstracts

Quaas et al. 2020, submitted

Quaas, J., A. Arola, B. Cairns, M. Christensen, H. Deneke, A.M.L. Ekman, G. Feingold, A. Fridlind, E. Gryspeerdt, O. Hasekamp, Z. Li, A. Lipponen, P.-L. Ma, J. Mülmenstädt, A. Nenes, J. Penner, D. Rosenfeld, R. Schrödner, K. Sinclair, O. Sourdeval, P. Stier, M. Tesche, B. van Diedenhoven, and M. Wendisch, 2020: Constraining the Twomey effect from satellite observations: Issues and perspectives. Atmos. Chem. Phys., submitted, doi:10.5194/acp-2020-279.

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 which also comprises rapid adjustments. 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) 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 vertical wind and by droplet sink processes. These operate at scales on the order of 10s of metres at which only localized observations are available and at which no approach exists yet 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 three key uncertainties in determining ΔNd,ant, namely the quantification (i) of the cloud-active aerosol — the cloud condensation nuclei concentrations (CCN) at or above cloud base —, (ii) of Nd sink processes, for which empirical assessments for specific cloud regimes are currently the best solutions. These considerations point to the conclusion that past studies using existing approaches have likely underestimated the true sensitivity and, thus, the radiative forcing due to the Twomey effect.

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BibTeX Citation

  author={Quaas, J. and Arola, A. and Cairns, B. and Christensen, M. and Deneke, H. and Ekman, A. M. L. 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.},
  title={Constraining the Twomey effect from satellite observations: Issues and perspectives},
  journal={Atmos. Chem. Phys.},
  note={Manuscript submitted for publication}

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RIS Citation

ID  - qu00100k
AU  - Quaas, J.
AU  - Arola, A.
AU  - Cairns, B.
AU  - Christensen, M.
AU  - Deneke, H.
AU  - Ekman, A. M. L.
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.
PY  - 2020
TI  - Constraining the Twomey effect from satellite observations: Issues and perspectives
JA  - Atmos. Chem. Phys.
DO  - 10.5194/acp-2020-279
ER  -

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