29 Apr 2022
29 Apr 2022

Implementation and evaluation of the GEOS-Chem chemistry module version 13.1.2 within the Community Earth System Model v2.1

Thibaud M. Fritz1, Sebastian D. Eastham1,2, Louisa K. Emmons3, Haipeng Lin4, Elizabeth W. Lundgren4, Steve Goldhaber3, Steven R. H. Barrett1,2, and Daniel J. Jacob4 Thibaud M. Fritz et al.
  • 1Laboratory for Aviation and the Environment, Department of Aeronautics and Astronautics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
  • 2Joint Program on the Science and Policy of Global Change, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
  • 3Atmospheric Chemistry Observations and Modeling Laboratory, National Center for Atmospheric Research, Boulder, CO, USA
  • 4John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA

Abstract. We implement the GEOS-Chem chemistry module as a chemical mechanism in the Community Earth System Model version 2 (CESM). Our implementation allows the state-of-the-science GEOS-Chem chemistry module to be used with identical emissions, meteorology, and climate feedbacks as the CAM-chem chemistry module within CESM. We use coupling interfaces to allow GEOS-Chem to operate almost unchanged within CESM. Aerosols are converted at each time step between the GEOS-Chem bulk representation and the size-resolved representation of CESM’s Modal Aerosol Model (MAM4). Land type information needed for dry deposition calculations in GEOS-Chem is communicated through a coupler, allowing online land-atmosphere interactions. Wet scavenging in GEOS-Chem is replaced with the Neu and Prather scheme, and a common emissions approach is developed for both CAM-chem and GEOS-Chem in CESM.

We compare how GEOS-Chem embedded in CESM (C-GC) compares to the existing CAM-chem chemistry option (C-CC) when used to simulate atmospheric chemistry in 2016, with identical meteorology and emissions. We compare atmospheric composition and deposition tendencies between the two simulations and evaluate the residual differences between C-GC compared to its use as a standalone chemistry transport model (S-GC). We find that stratospheric ozone agrees well between the three models with differences of less than 10 % in the core of the ozone layer, but that ozone at lower altitudes is generally lower in C-GC than in either C-CC or S-GC due to greater tropospheric concentrations of bromine. This difference is not uniform, with C-GC ozone 30 % lower in the southern hemisphere than in S-GC but within 10 % in the northern hemisphere, suggesting differences in the effects of anthropogenic emissions. Aerosol concentrations in C-GC agree with those in S-GC at low altitudes in the tropics but are over 100 % greater in the upper troposphere due to differences in the representation of convective scavenging. We also find that water vapor concentrations vary substantially between the standalone and CESM-implemented version of GEOS-Chem, as the simulated hydrological cycle in CESM diverges from that represented in the source MERRA-2 meteorology.

Our implementation of GEOS-Chem as a chemistry option in CESM (including full chemistry-climate feedbacks) is publicly available and is being considered for inclusion in the CESM main code repository. This work is a significant step in the MUlti-Scale Infrastructure for Chemistry and Aerosols (MUSICA) project, enabling two communities of atmospheric researchers (CESM and GEOS-Chem) to share expertise through a common modeling framework and thereby accelerate progress in atmospheric science.

Thibaud M. Fritz et al.

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-2022-226', Katherine Emma Knowland, 14 Jun 2022
    • AC1: 'Response to reviewers', Sebastian Eastham, 22 Aug 2022
  • RC2: 'Comment on egusphere-2022-226', Anonymous Referee #2, 19 Jun 2022
    • AC1: 'Response to reviewers', Sebastian Eastham, 22 Aug 2022
  • AC1: 'Response to reviewers', Sebastian Eastham, 22 Aug 2022

Thibaud M. Fritz et al.

Model code and software

GEOS-Chem version 13.1.2 within CESM v2.1 Fritz, Eastham, Emmons, Lin, Lundgren, Goldhaber, Barrett, and Jacob

Thibaud M. Fritz et al.


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Short summary
We bring the state-of-the-science chemistry module GEOS-Chem into the Community Earth System Model (CESM). We show that some known differences between results from GEOS-Chem and CESM’s CAM-chem chemistry module may be due to the configuration of model meteorology rather than inherent differences in the model chemistry. This is a significant step towards a truly modular ESM and allows two strong but currently separate research communities to benefit from each other’s advances.