Preprints
https://doi.org/10.5194/acp-2021-329
https://doi.org/10.5194/acp-2021-329

  18 Jun 2021

18 Jun 2021

Review status: this preprint is currently under review for the journal ACP.

Exploring the uncertainties in the aviation soot-cirrus effect

Mattia Righi, Johannes Hendricks, and Christof Gerhard Beer Mattia Righi et al.
  • Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany

Abstract. A global aerosol-climate model, including a two-moment cloud microphysical scheme and a parametrization for aerosol-induced ice formation in cirrus clouds, is applied in order to quantify the impact of aviation soot on natural cirrus clouds. Several sensitivity experiments are performed to assess the uncertainties in this effect related to (i) the assumptions on the ice nucleation abilities of aviation soot; (ii) the representation of vertical updrafts in the model; and (iii) the use of reanalysis data to relax the model dynamics (the so-called nudging technique). Based on the results of the model simulations, a radiative forcing from the aviation soot-cirrus effect in the range of −35 mW m−2 to 13 mW m−2 is quantified, depending on the assumed critical saturation ratio for ice nucleation and active fraction of aviation soot, but with a confidence level below 95 % in several cases. Simple idealized experiments with prescribed vertical velocities further show that the uncertainties on this aspect of the model dynamics are critical for the investigated effect and could potentially add a factor of about two of further uncertainty to the model estimates of the resulting radiative forcing. The use of the nudging technique to relax model dynamics is proved essential in order to identify a statistically significant signal from the model internal variability, while simulations performed in free-running mode and with prescribed sea-surface temperatures and sea-ice concentrations are shown to be unable to provide robust estimates of the investigated effect. A comparison with analogous model studies on the aviation-soot cirrus effect show a very large model diversity, with a conspicuous lack of consensus across the various estimates, which points to the need for more in-depth analyses on the roots of such discrepancies.

Mattia Righi et al.

Status: open (until 30 Jul 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on acp-2021-329', Bernd Kärcher, 25 Jun 2021 reply
  • RC1: 'Comment on acp-2021-329', Andrew Gettelman, 30 Jun 2021 reply
  • RC2: 'Comment on acp-2021-329', Anonymous Referee #1, 08 Jul 2021 reply

Mattia Righi et al.

Mattia Righi et al.

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Short summary
A global climate model is applied to simulate the impact of aviation soot on natural cirrus clouds. A large number of numerical experiments is performed to analyse how the quantification of the resulting climate impact is affected by known uncertainties. These concern the ability of aviation soot to nucleate ice and the role of model dynamics. Our results show that both aspects are important for the quantification of this effect and that discrepancies among different model studies still exist.
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