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Title: What controls the vertical distribution of aerosol? Relationships between process sensitivity in HadGEM3–UKCA and inter-model variation from AeroCom Phase II

The vertical profile of aerosol is important for its radiative effects, but weakly constrained by observations on the global scale, and highly variable among different models. To investigate the controlling factors in one particular model, we investigate the effects of individual processes in HadGEM3–UKCA and compare the resulting diversity of aerosol vertical profiles with the inter-model diversity from the AeroCom Phase II control experiment. In this way we show that (in this model at least) the vertical profile is controlled by a relatively small number of processes, although these vary among aerosol components and particle sizes. We also show that sufficiently coarse variations in these processes can produce a similar diversity to that among different models in terms of the global-mean profile and, to a lesser extent, the zonal-mean vertical position. However, there are features of certain models' profiles that cannot be reproduced, suggesting the influence of further structural differences between models. In HadGEM3–UKCA, convective transport is found to be very important in controlling the vertical profile of all aerosol components by mass. In-cloud scavenging is very important for all except mineral dust. Growth by condensation is important for sulfate and carbonaceous aerosol (along with aqueous oxidation for the former andmore » ageing by soluble material for the latter). The vertical extent of biomass-burning emissions into the free troposphere is also important for the profile of carbonaceous aerosol. Boundary-layer mixing plays a dominant role for sea salt and mineral dust, which are emitted only from the surface. Dry deposition and below-cloud scavenging are important for the profile of mineral dust only. In this model, the microphysical processes of nucleation, condensation and coagulation dominate the vertical profile of the smallest particles by number (e.g. total CN > 3 nm), while the profiles of larger particles (e.g. CN > 100 nm) are controlled by the same processes as the component mass profiles, plus the size distribution of primary emissions. Here, we also show that the processes that affect the AOD-normalised radiative forcing in the model are predominantly those that affect the vertical mass distribution, in particular convective transport, in-cloud scavenging, aqueous oxidation, ageing and the vertical extent of biomass-burning emissions.« less
 [1] ;  [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [6] ;  [7] ;  [8] ;  [9] ;  [10] ;  [11] ;  [6] ;  [12] ;  [13] ;  [14] ;  [3] ;  [15] ;  [11] ;  [11] more »;  [16] ;  [17] ;  [5] ;  [18] « less
  1. Univ. of Oxford, Oxford (United Kingdom)
  2. Met Office Hadley Centre, Exeter (United Kingdom)
  3. Univ. of Leeds, Leeds (United Kingdom)
  4. Univ. of Reading, Reading (United Kingdom)
  5. Columbia Univ., New York, NY (United States); NASA Goddard Inst. for Space Studies (GISS), New York, NY (United States)
  6. Finnish Meteorological Institute, Kuopio (Finland)
  7. NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States)
  8. European Commission, Ispra (Italy). Joint Research Centre
  9. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
  10. Norwegian Meteorological Institute, Oslo (Norway); Univ. of Oslo, Oslo (Norway)
  11. Norwegian Meteorological Institute, Oslo (Norway)
  12. Univ. of Wyoming, Laramie, WY (United States)
  13. State Univ. of New York (SUNY), Albany, NY (United States)
  14. Royal Netherlands Meteorological Institute, De Bilt (The Netherlands)
  15. Canadian Centre for Climate Modelling and Analysis, Victoria, BC (Canada)
  16. Center for International Climate and Environmental Research - Oslo (CICERO), Oslo (Norway)
  17. Kyushu Univ., Fukuoka (Japan)
  18. Max Planck Inst. for Meteorology, Hamburg (Germany); Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Publication Date:
Report Number(s):
Journal ID: ISSN 1680-7324; KP1703010
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Atmospheric Chemistry and Physics (Online)
Additional Journal Information:
Journal Name: Atmospheric Chemistry and Physics (Online); Journal Volume: 16; Journal Issue: 4; Journal ID: ISSN 1680-7324
European Geosciences Union
Research Org:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org:
Country of Publication:
United States
OSTI Identifier: