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Discussion papers
https://doi.org/10.5194/gmd-2019-357
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/gmd-2019-357
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: model evaluation paper 25 Mar 2020

Submitted as: model evaluation paper | 25 Mar 2020

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This preprint is currently under review for the journal GMD.

Description and evaluation of aerosol in UKESM1 and HadGEM3-GC3.1 CMIP6 historical simulations

Jane P. Mulcahy1, Colin Johnson1,2, Colin G. Jones2, Adam C. Povey3, Catherine E. Scott4, Alistair Sellar1, Steven T. Turnock1, Matthew T. Woodhouse5, N. Luke Abraham6,11, Martin B. Andrews1, Nicolas Bellouin7, Jo Browse4,a, Ken S. Carslaw4, Mohit Dalvi1, Gerd A. Folberth1, Matthew Glover1, Daniel Grosvenor4, Catherine Hardacre1, Richard Hill1, Ben Johnson1, Andy Jones1, Zak Kipling8,b, Graham Mann4, James Mollard7, Fiona M. O'Connor1, Julien Palmieri9, Carly Reddington4, Steven T. Rumbold10, Mark Richardson4, Nick A. J. Schutgens8,c, Philip Stier8, Marc Stringer10, Yongming Tang1, Jeremy Walton1, Stephanie Woodward1, and Andrew Yool9 Jane P. Mulcahy et al.
  • 1Met Office Hadley Centre, Exeter, UK, EX1 3PB
  • 2National Centre for Atmospheric Science, University of Leeds, UK
  • 3National Centre for Earth Observation, University of Oxford, OX1 3PU, UK
  • 4School of Earth and Environment, University of Leeds, UK
  • 5CSIRO Climate Science Centre, Aspendale, Victoria, Australia
  • 6National Centre for Atmospheric Science, University of Cambridge, UK
  • 7Department of Meteorology, University of Reading, UK
  • 8Atmospheric, Oceanic and Planetary Physics, Department of Physics, University of Oxford, UK
  • 9National Oceanography Centre, Southampton, UK
  • 10National Centre for Atmospheric Science, University of Reading, UK
  • 11Department of Chemistry, University of Cambridge, Cambridge, UK, CB2 1EW
  • anow at: University of Exeter, Penryn, UK
  • bnow at: ECMWF, Shinfield Park, Reading, RG2 9AX, UK
  • cnow at: Earth Sciences, Faculty of Science, Vrije Universiteit Amsterdam, Amsterdam, the Netherlands

Abstract. We document and evaluate the aerosol schemes as implemented in the physical and Earth system models, HadGEM3-GC3.1 (GC3.1) and UKESM1, which are contributing to the 6th Coupled Model Intercomparison Project (CMIP6). The simulation of aerosols in the present-day period of the historical ensemble of these models is evaluated against a range of observations. Updates to the aerosol microphysics scheme are documented as well as differences in the aerosol representation between the physical and Earth system configurations. The additional Earth-system interactions included in UKESM1 leads to differences in the emissions of natural aerosol sources such as dimethyl sulfide, mineral dust and organic aerosol and subsequent evolution of these species in the model. UKESM1 also includes a stratospheric-tropospheric chemistry scheme which is fully coupled to the aerosol scheme, while GC3.1 employs a simplified aerosol chemistry mechanism driven by prescribed monthly climatologies of the relevant oxidants. Overall, the simulated speciated aerosol mass concentrations compare reasonably well with observations. Both models capture the negative trend in sulfate aerosol concentrations over Europe and the eastern United States of America (US) although the models tend to underestimate the sulfate concentrations in both regions. Interactive emissions of biogenic volatile organic compounds in UKESM1 lead to an improved agreement of organic aerosol over the US. Simulated dust burdens are similar in both models despite a 2-fold difference in dust emissions. Aerosol optical depth is biased low in dust source and outflow regions but performs well in other regions compared to a number of satellite and ground-based retrievals of aerosol optical depth. Simulated aerosol number concentrations are generally within a factor of 2 of the observations with both models tending to overestimate number concentrations over remote ocean regions, apart from at high latitudes, and underestimate over Northern Hemisphere continents. Finally, UKESM1 includes for the first time a representation of a primary marine organic aerosol source. The impact of this new aerosol source is evaluated. Over the pristine Southern Ocean, it is found to improve the seasonal cycle of organic aerosol mass and cloud droplet number concentrations relative to GC3.1 although underestimations in cloud droplet number concentrations remain. This paper provides a useful characterization of the aerosol climatology in both models facilitating the understanding of the numerous aerosol-climate interaction studies that will be conducted as part of CMIP6 and beyond.

Jane P. Mulcahy et al.

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Status: open (until 20 May 2020)
Status: open (until 20 May 2020)
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Jane P. Mulcahy et al.

Data sets

CMIP6.CMIP.MOHC.UKESM1-0-LL.historical Y. Tang, S. Rumbold, R. Ellis, D. Kelley, J. Mulcahy, A. Sellar, J. Walton, and C. Jones https://doi.org/10.22033/ESGF/CMIP6.6113

CMIP6.CMIP.MOHC.HadGEM3-GC31-LL.historical J. Ridley, M. Menary, T. Kuhlbrodt, M. Andrews, and T. Andrews https://doi.org/10.22033/ESGF/CMIP6.6109

CMIP6.CMIP.MOHC.UKESM1-0-LL.amip Y. Tang, S. Rumbold, R. Ellis, D. Kelley, J. Mulcahy, A. Sellar, J. Walton, and C. Jones https://doi.org/10.22033/ESGF/CMIP6.5857

Jane P. Mulcahy et al.

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Short summary
This manuscript provides the most up-to-date documentation and evaluation of the aerosol schemes as implemented in the physical and Earth system models, HadGEM3- GC3.1 and UKESM1. It provides a useful characterization of the aerosol climatology in both models facilitating the understanding of the numerous aerosol-climate interaction studies that will be conducted as part of CMIP6 and beyond.
This manuscript provides the most up-to-date documentation and evaluation of the aerosol schemes...
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