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Publication Date
15 April 2024

Modes of Variability in E3SM and CESM Large Ensembles

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Internal modes of climate variability are a central consideration for both seasonal climate prediction and climate change
detection and attribution yet the fidelity in representing key modes varies widely across climate models. In this work, the
Climate Variability Diagnostics Package for Large Ensembles (CVDP-LE) developed at NCAR is applied to four recently
produced large ensembles with the goal of intercomparing E3SM and CESM versions 1 and 2.


Enabled by the opportunities provided by large ensembles, the analysis quantifies the strengths and weaknesses of each
model version in reproducing observed modes of variability. In addition, the ensembles provide insight into the intrinsic
noise of modes and the associated limitations that exist in diagnosing these modes with the observational record, which is
of finite duration. When model performance is considered in aggregate, the ensembles show measurable improvement
from versions 1 to 2, with both E3SM2 and CESM2 scoring among the top tier of currently available climate models.


The representation of global coupled modes is found to improve across successive E3SM and CESM versions in
conjunction with the fidelity of the base state climate while the patterns of extratropical modes are well simulated across
the ensembles. Various persistent shortcomings for all MoV are however identified and discussed. The results both
demonstrate the successes of these recent model versions and suggest the potential for continued improvement in the
representation of MoV with advances in model physics.

Point of Contact
John Fasullo
National Center for Atmospheric Research (NCAR)
Funding Program Area(s)
Modes of Variability in E3SM and CESM Large Ensembles
Fasullo, John T., Julie M. Caron, Adam Phillips, Hui Li, Jadwiga H. Richter, Richard B. Neale, Nan A Rosenbloom, et al. 2024. “Modes Of Variability In E3Sm And Cesm Large Ensembles”. Journal Of Climate 37 (8). American Meteorological Society: 2629-2653. doi:10.1175/jcli-d-23-0454.1.