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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Preprints
https://doi.org/10.5194/acp-2020-68
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2020-68
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  21 Feb 2020

21 Feb 2020

Review status
A revised version of this preprint was accepted for the journal ACP and is expected to appear here in due course.

Improving aerosol activation in the double-moment Unified Model with CLARIFY measurements

Hamish Gordon1,2, Paul R. Field1,3, Steven J. Abel3, Paul Barrett3, Keith Bower4, Ian Crawford4, Zhiqiang Cui1, Daniel P. Grosvenor1, Adrian A. Hill3, Jonathan Taylor4, Jonathan Wilkinson3, Huihui Wu4, and Ken S. Carslaw1 Hamish Gordon et al.
  • 1School of Earth and Environment, University of Leeds, LS2 9JT, United Kingdom
  • 2Engineering Research Accelerator, Carnegie Mellon University, Forbes Avenue, Pittsburgh 15213, United States
  • 3Met Office, Fitzroy Road, Exeter, EX1 3PB, United Kingdom
  • 4Department of Earth and Environmental Sciences, University of Manchester, M13 9PL, United Kingdom

Abstract. Representing the number and mass of cloud and aerosol particles independently in a climate, weather prediction or air quality model is important in order to simulate aerosol direct and indirect effects on radiation balance. Here we introduce the first configuration of the UK Met Office Unified Model in which both cloud and aerosol particles have double-moment representations with prognostic number and mass. The GLOMAP aerosol microphysics scheme, already used in the HadGEM3 climate configuration, is coupled to the CASIM cloud microphysics scheme. We demonstrate the performance of the new configuration in cloud-resolving simulations of a case study defined from the CLARIFY aircraft campaign in 2017 near Ascension Island in the tropical south Atlantic. We improve the physical basis of the activation scheme by representing the effect of existing cloud droplets on the activation of new aerosol, and we also attempt to account for the effect of unresolved vertical velocities. The first of these improvements should be applicable to the representation of aerosol activation in other microphysics schemes. While these changes lead only to a modest improvement in model performance, they reinforce our confidence in the ability of the model to simulate aerosol-cloud microphysical interactions. Capturing these interactions accurately is critical to simulating aerosol effects on climate.

Hamish Gordon et al.

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AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Interactive discussion

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Hamish Gordon et al.

Hamish Gordon et al.

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Latest update: 11 Aug 2020
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Short summary
The Met Office's Unified Model is widely used both for weather forecasting and climate prediction. We present the first version of the model in which both aerosol and cloud particle mass and number concentrations are allowed to evolve separately and independently, which is important for studying how aerosols affect weather and climate. We test the model against aircraft observations near Ascension Island in the Atlantic, focusing on how aerosols can activate to become cloud droplets.
The Met Office's Unified Model is widely used both for weather forecasting and climate...
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