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© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  08 Jul 2020

08 Jul 2020

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

The nature of ice-nucleating particles affects the radiative properties of tropical convective cloud systems

Rachel E. Hawker1, Annette K. Miltenberger1,a, Jonathan M. Wilkinson2, Adrian A. Hill2, Ben J. Shipway2, Zhiqiang Cui1, Richard J. Cotton2, Ken S. Carslaw1, Paul R. Field1,2, and Benjamin J. Murray1 Rachel E. Hawker et al.
  • 1Institute for Climate and Atmospheric Science, University of Leeds, Leeds, LS2 9JT, UK
  • 2Met Office, Exeter, EX1 3PB, UK
  • anow at: Institute for Atmospheric Physics, Johannes Gutenberg University Mainz, Mainz, 55128, Germany

Abstract. Convective cloud systems in the maritime tropics play a critical role in global climate, but accurately representing aerosol interactions within these clouds persists as a major challenge for weather and climate modelling. We quantify the effect of ice-nucleating particles (INP) on the radiative properties of a complex Tropical Atlantic deep convective cloud field using a regional model with an advanced double-moment microphysics scheme. Our results show that the domain-mean daylight outgoing radiation varies by up to 18 W m−2 depending on the bio- and physico-chemical properties of INP. The key distinction between different INPs is the temperature dependence of ice formation, which alters the vertical distribution of cloud microphysical processes. The controlling effect of the INP temperature dependence is substantial even in the presence of secondary ice production, and the effects of secondary ice formation depend strongly on the nature of the INP. Our results have implications for climate model simulations of tropical clouds and radiation, which currently do not consider a link between INP particle type and ice water content. The results also provide a challenge to the INP measurement community, since we demonstrate that INP concentration measurements are required over the full mixed-phase temperature regime, which covers around 10 orders of magnitude in INP concentration.

Rachel E. Hawker et al.

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Rachel E. Hawker et al.

Rachel E. Hawker et al.


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Latest update: 29 Sep 2020
Publications Copernicus
Short summary
The impact of aerosols on clouds, including mixed-phase clouds, is a large source of uncertainty for future climate projections. Our results show that the reflectivity of a convective cloud field is sensitive to the presence and efficiency of ice-nucleating particles in the Saharan outflow region. Differences in aerosol source or composition, for the same aerosol size distribution, can cause differences in the outgoing radiation from regions dominated by tropical convection.
The impact of aerosols on clouds, including mixed-phase clouds, is a large source of uncertainty...