Preprints
https://doi.org/10.5194/egusphere-2023-2783
https://doi.org/10.5194/egusphere-2023-2783
30 Nov 2023
 | 30 Nov 2023

Developing a climatological simplification of aerosols to enter the cloud microphysics of a global climate model

Ulrike Proske, Sylvaine Ferrachat, and Ulrike Lohmann

Abstract. Aerosol particles influence cloud formation and properties. Hence climate models that aim for a physical representation of the climate system include aerosol modules. In order to represent more and more processes and aerosol species, their representation has grown increasingly detailed. However, depending on one's modeling purpose, the increased model complexity may not be beneficial, for example because it hinders understanding of model behaviour. Hence we develop a simplification in the form of a climatology of aerosol concentrations. In one approach, the climatology prescribes properties important for cloud droplet and ice crystal formation, the gateways for aerosols to enter the model cloud microphysics scheme. Another approach prescribes aerosol mass and number concentrations in general. Both climatologies are derived from full ECHAM-HAM simulations and can serve to replace the HAM aerosol module and thus drastically simplify the aerosol treatment. The first simplification reduces computational model time by roughly 65 %. However, the naive mean climatological treatment needs improvement to give results that are satisfyingly close to the full model. We find that mean CCN concentrations yield an underestimation of CDNC in the Southern Ocean, which we can reduce by allowing only CCN at cloud base (which have experienced hygroscopic growth in these conditions) to enter the climatology. This highlights the value of the simplification approach in pointing to unexpected model behaviour and providing a new perspective for its study and model development.

Ulrike Proske, Sylvaine Ferrachat, and Ulrike Lohmann

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-2783', Anonymous Referee #1, 03 Jan 2024
    • AC1: 'Reply on RC1 and RC2', Ulrike Proske, 23 Feb 2024
  • RC2: 'Comment on egusphere-2023-2783', Anonymous Referee #2, 03 Jan 2024
    • AC1: 'Reply on RC1 and RC2', Ulrike Proske, 23 Feb 2024
Ulrike Proske, Sylvaine Ferrachat, and Ulrike Lohmann
Ulrike Proske, Sylvaine Ferrachat, and Ulrike Lohmann

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Short summary
Climate models include treatment of aerosol particles because these influence clouds and radiation. Over time their representation has grown increasingly detailed. This complexity may hinder our understanding of model behaviour. Thus here we simplify the aerosol representation of our climate model by prescribing a mean concentration, which saves runtime and helps to discover unexpected model behaviour. We conclude that simplifications provide a new perspective for model study and development.