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Discussion papers | Copyright
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Development and technical paper 31 May 2018

Development and technical paper | 31 May 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Geoscientific Model Development (GMD).

A production-tagged aerosol module for earth system models, OsloAero5.3 – extensions and updates for CAM5.3-Oslo

Alf Kirkevåg1, Alf Grini1, Dirk Olivié1, Øyvind Seland1, Kari Alterskjær2,3, Matthias Hummel3, Inger H. H. Karset3, Anna Lewinschal4, Xiaohong Liu5, Risto Makkonen6, Ingo Bethke7, Jan Griesfeller1, Michael Schulz1, and Trond Iversen1,2 Alf Kirkevåg et al.
  • 1Norwegian Meteorological Institute, P.O. Box 43, Blindern, 0313 Oslo, Norway
  • 2CICERO Center for International Climate Research, 0349 Oslo, Norway
  • 3Department of Geosciences, Section for Meteorology and Oceanography, University of Oslo, 1022 Oslo, Norway
  • 4Department of Meteorology, Stockholm University, 106 91 Stockholm, Sweden
  • 5Department of Atmospheric Science, University of Wyoming, Laramie, Wyoming, 82071, USA
  • 6Dept. of Physics, University of Helsinki, P.O. Box 64, Helsinki, Finland
  • 7Uni Research Climate, Bjerknes Centre for Climate Research, P.O. Box 7810, 5020 Bergen, Norway

Abstract. We here document model updates, and present and discuss modelling and validation results, from a further developed production tagged aerosol module, OsloAero5.3, for use in earth system models. The aerosol module has in this study been implemented and applied in CAM5.3-Oslo. This model is based on CAM5.3/CESM1.2 and its own predecessor model version CAM4-Oslo. OsloAero5.3 has improved treatment of emissions, aerosol chemistry, particle lifecycle and aerosol-cloud interactions compared to its predecessor OsloAero4.0 in CAM4-Oslo. The main new features consist of improved aerosol sources, the module now explicitly accounting for aerosol particle nucleation and secondary organic aerosol production, with also new emissions schemes for sea-salt, dimethyl sulphide (DMS) and marine primary organics. Mineral dust emissions are updated as well, adopting the formulation of CESM1.2. The improved model representation of aerosol-cloud interactions now resolves heterogeneous ice nucleation based on black carbon (BC) and mineral dust calculated by the model, and treats activation of cloud condensation nuclei (CCN) as in CAM5.3. Compared to OsloAero4.0 in CAM4-Oslo, the black carbon (BC) mass concentrations are less excessive aloft, with better fit to observations. Near surface mass concentrations of BC and sea-salt aerosols are also less biased, while sulfate and mineral dust are slightly more biased. Although appearing quite similar for CAM5.3-Oslo and CAM4-Oslo, the validation results for organic matter (OM) are inconclusive, since both of the respective versions of OsloAero are equipped with a limited number of OM tracers for the sake of computational efficiency. Any information about the assumed mass ratios of OM to organic carbon (OC) for different types of OM sources is lost in the transport module. Assuming that observed OC concentrations scaled by 1.4 are representative for the modeled OM concentrations, CAM5.3-Oslo with OsloAero5.3 is slightly inferior for the very sparsely available observation data. Comparing clear-sky column integrated optical properties with data from ground based remote sensing, we find a negative bias in optical depth globally, however not as strong as in CAM4-Oslo, while it is biased high for areas typically dominated by mineral dust emissions. Aerosol absorption has a larger negative bias than the optical depth globally, and is less overestimated in areas where mineral dust is the main contributor to absorption. Globally, the low bias in absorption is smaller than in CAM4-Oslo. The Ångström parameter exhibits small biases both globally and regionally, suggesting that the aerosol particle sizes are reasonably well represented. Cloud top droplet number concentrations over oceans are generally underestimated compared to satellite retrievals, but seem to be overestimated downwind of major emissions of dust and biomass burning sources. Finally we find small changes in direct radiative forcing at top of the atmosphere, while the cloud radiative forcing due to anthropogenic aerosols is now more negative than in CAM4-Oslo, being on the strong side compared to the multi-model estimate in IPCC AR5. Although not all validation results in this study show improvement for the present CAM5.3-Oslo version, the extended and updated aerosol module OsloAero5.3 is more advanced and applicable than its predecessor OsloAero4.0, as it includes new parameterizations which more readily facilitate sensitivity and process studies and use in climate and earth system model studies in general.

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Alf Kirkevåg et al.
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Alf Kirkevåg et al.
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Short summary
A new aerosol treatment is described and tested in a global climate model. With updated emissions, aerosol chemistry and microphysics compared to its predecessor, black carbon (BC) mass concentrations aloft better fits observations, surface concentrations of BC and sea-salt are less biased, sulfate and mineral dust slightly more, while results for organics are inconclusive. Man-made aerosols now yield a stronger cooling effect on climate, being on the strong side compared to results from IPCC.
A new aerosol treatment is described and tested in a global climate model. With updated...