Mahfouz et al. (2025) Prescribing the aerosol effective radiative forcing in the Simple Cloud-Resolving E3SM Atmosphere Model v1

Identification

• Journal: Atmospheric chemistry and physics
• Year: 2025
• Date: 2025-11-07
• Authors: Naser Mahfouz, Hassan Beydoun, Johannes Mülmenstädt, Noel D. Keen, Adam Varble, Luca Bertagna, Peter Bogenschutz, Andrew Bradley, Matthew W. Christensen, Thomas C Clevenger, Aaron S. Donahue, Jerome D. Fast, James Foucar, Jean‐Christophe Golaz, Oksana Guba, Walter M. Hannah, Benjamin Hillman, Robert Jacob, Weiren Lin, Po‐Lun Ma, Yun Qian, Balwinder Singh, Christopher R. Terai, Hailong Wang, Mingxuan Wu, Kai Zhang, Andrew Gettelman, Mark A. Taylor, L. Ruby Leung, Peter Caldwell, Susannah M. Burrows
• DOI: 10.5194/acp-25-15105-2025

Research Groups

• Pacific Northwest National Laboratory, Richland, WA, USA
• Lawrence Livermore National Laboratory, Livermore, CA, USA
• Lawrence Berkeley National Laboratory, Berkeley, CA, USA
• Sandia National Laboratories, Albuquerque, NM, USA
• Argonne National Laboratory, Lemont, IL, USA
• Brookhaven National Laboratory, Upton, NY, USA

Short Summary

This study assesses the sensitivity of aerosol effective radiative forcing (ERFaer) to anthropogenic aerosol changes in the Simple Cloud-Resolving E3SM Atmosphere Model (SCREAM) v1 using a prescribed aerosol scheme. It finds that while the default scheme initially overestimates forcing, parameterization adjustments in aerosol activation enable SCREAM v1 to reproduce the reference model's ERFaer across resolutions.

Objective

• To assess whether the high-resolution SCREAM v1 configuration can reproduce the aerosol effective radiative forcing (ERFaer) from pre-industrial to present-day conditions, using a simplified prescribed aerosol (SPA) scheme derived from a low-resolution model, similar to that produced by low-resolution models with fully interactive aerosols.
• To quantify the global ERFaer, focusing on the dominant aerosol–cloud interactions, and understand its sensitivity to model resolution and aerosol activation assumptions.

Study Configuration

• Spatial Scale:
  • SCREAM v1 simulations: 3 km and 12 km horizontal grid spacing.
  • E3SM v3 reference simulations: 100 km effective horizontal resolution (150 km near the equator), 80 vertical levels.
• Temporal Scale:
  • E3SM v3 reference (for SPA climatology): 31 years (30 years used for climatological monthly means).
  • SCREAM v1 sensitivity simulations: 13 months (1 August 2019 to 1 September 2020, first month discarded).
  • E3SM v3 nudged sensitivity simulations: 13 months (1 December 2009 to 1 January 2011, first month discarded).

Methodology and Data

• Models used:
  • Energy Exascale Earth System Model (E3SM) Simple Cloud-Resolving E3SM Atmosphere Model (SCREAM) v1.
  • E3SM v3 coarse-resolution atmosphere model (E3SM-MAM v3 with interactive aerosols, E3SM-SPA v3 with prescribed aerosols).
  • Simplified Prescribed Aerosol (SPA) scheme (derived from E3SM v3).
  • Modal Aerosol Model (MAM) scheme (MAM4-based in E3SM v3).
  • Cloud microphysics: Modified Predicted Particle Properties (P3) scheme.
  • Cloud macrophysics and turbulent vertical mixing: Simplified Higher-Order Closure (SHOC) in SCREAM v1; Cloud Layers Unified By Binomials (CLUBB) in E3SM v3.
  • Radiation scheme: RRTMGP in SCREAM v1; RRTMG in E3SM v3.
  • Convection: No parameterized deep convection in SCREAM v1; Zhang and McFarlane (1995) type in E3SM v3.
• Data sources:
  • Sea surface temperature (SST) and sea ice coverage: Operational Sea Surface Temperature and Ice Analysis (OSTIA) and The European Organization for the Exploitation of Meteorological Satellite Ocean and Sea Ice Satellite Application Facility (UKMO).
  • Atmosphere initial conditions: Fifth-generation European Centre for Medium-Range Weather Forecasts atmospheric reanalyses (ERA5) data (0.25° × 0.25° horizontal resolution).
  • Land initial conditions: CRUNCEP data.
  • Nudging data: Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2) reanalysis data (6 h temporal, 0.5° × 0.625° horizontal resolution).

Main Results

• The default SCREAM v1 configuration with the SPA scheme produces a significantly more negative globally averaged ERFaer (e.g., -1.89 W m⁻² for 3 km, -1.95 W m⁻² for 12 km) compared to the reference E3SM v3 (approximately -0.74 W m⁻²).
• The globally averaged ERFaer signal exhibits little overall resolution sensitivity between 3 km and 12 km, but regional resolution dependencies are observed (e.g., more negative over convectively active land regions at 12 km, more negative in marine stratocumulus regions at 3 km).
• The ERFaer signal is predominantly driven by aerosol–cloud interactions (indirect effects), accounting for approximately 90% of the total, with the Twomey effect being the most important component. Aerosol–radiation interactions (direct effects) are relatively minor.
• The default linear aerosol activation formulation (α = NccnCf) in the SPA scheme overestimates cloud droplet sensitivity to aerosol perturbations.
• The Nc limiter (in-cloud Nc ≥ 20 cm⁻³) in E3SM v3 contributes approximately 0.40 W m⁻² to the global average ERFaer.
• By adjusting the aerosol activation parameterization in SPA to a sublinear relationship (α = 2000(NccnCf)⁰.⁵⁵), the global ERFaer signal in E3SM-SPA v3 is successfully reconciled with the E3SM-MAM v3 reference. This modified formulation will be adopted as the default.
• The revised activation formulation leads to an approximate 40% decrease in present-day cloud-top cloud droplet number concentration (Nc) and a 66% decrease in present-day minus pre-industrial (PD-PI) differences compared to the default linear formulation.

Contributions

• Demonstrates the feasibility of constraining global aerosol effective radiative forcing (ERFaer) across different resolutions and model configurations using a simple prescribed aerosol (SPA) scheme.
• Identifies that the global ERFaer in SCREAM v1 is primarily driven by indirect cloud effects, particularly the Twomey effect, and is highly sensitive to aerosol activation assumptions.
• Provides a refined aerosol activation parameterization for the SPA scheme in SCREAM v1, which accurately reproduces the ERFaer of the reference E3SM v3 model.
• Establishes a framework that leverages the adaptability of prescribed schemes for targeted hypothesis testing and controlled decoupling of aerosol–cloud interactions, enabling studies of extreme weather and climate feedbacks independent of aerosol forcing uncertainty.
• Facilitates high-resolution investigations of cloud responses to aerosol perturbations by eliminating complexities associated with interactive aerosol feedback mechanisms.
• Sets the groundwork for systematic identification of ERFaer deviation hotspots between simple (SPA) and complex (MAM) schemes, fostering process-level scrutiny and iterative model improvement.

Funding

• U.S. Department of Energy (DOE), Office of Science, Office of Biological and Environmental Research (E3SM project).
• Pacific Northwest National Laboratory (PNNL) under contract no. DE-AC06-76RLO1830.
• DOE Office of Science and Office of Biological and Environmental Research Earth System Model Development program area of the Earth and Environmental System Modeling program (for E3SM v3 simulations at Argonne National Laboratory's Laboratory Computing Resource Center).
• National Energy Research Scientific Computing Center (NERSC), Lawrence Berkeley National Laboratory, under contract no. DE-AC02-05CH11231 (NERSC award BER-ERCAP-0027116 for SCREAM v1 simulations).
• Sandia National Laboratories (National Technology & Engineering Solutions of Sandia, LLC) for the U.S. Department of Energy’s National Nuclear Security Administration (DOE/NNSA) under contract DE-NA0003525.
• Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
• Grant numbers: DE-AC06-76RLO1830, DE-AC02-05CH1123, DE-NA0003525, DE-AC52-07NA27344.

Citation

@article{Mahfouz2025Prescribing,
  author = {Mahfouz, Naser and Beydoun, Hassan and Mülmenstädt, Johannes and Keen, Noel D. and Varble, Adam and Bertagna, Luca and Bogenschutz, Peter and Bradley, Andrew and Christensen, Matthew W. and Clevenger, Thomas C and Donahue, Aaron S. and Fast, Jerome D. and Foucar, James and Golaz, Jean‐Christophe and Guba, Oksana and Hannah, Walter M. and Hillman, Benjamin and Jacob, Robert and Lin, Weiren and Ma, Po‐Lun and Qian, Yun and Singh, Balwinder and Terai, Christopher R. and Wang, Hailong and Wu, Mingxuan and Zhang, Kai and Gettelman, Andrew and Taylor, Mark A. and Leung, L. Ruby and Caldwell, Peter and Burrows, Susannah M.},
  title = {Prescribing the aerosol effective radiative forcing in the Simple Cloud-Resolving E3SM Atmosphere Model v1},
  journal = {Atmospheric chemistry and physics},
  year = {2025},
  doi = {10.5194/acp-25-15105-2025},
  url = {https://doi.org/10.5194/acp-25-15105-2025}
}