Lubis et al. (2025) Cloud radiative effects significantly increase wintertime atmospheric blocking in the Euro-Atlantic sector

Identification

• Journal: Nature Communications
• Year: 2025
• Date: 2025-11-05
• Authors: Sandro W. Lubis, Bryce E. Harrop, Jian Lu, L. Ruby Leung, Ziming Chen, Clare S. Y. Huang, Nour‐Eddine Omrani
• DOI: 10.1038/s41467-025-64672-9

Research Groups

• Pacific Northwest National Laboratory (Richland, WA, USA)
• College of Oceanic and Atmospheric Sciences and State Key Laboratory of Physical Oceanography, Ocean University of China (Qingdao, China)
• Epsilon Data Management LLC (Irving, TX, USA)
• Bjerknes Centre for Climate Research, University of Bergen (Bergen, Norway)
• National Center for Atmospheric Research (NCAR, USA)
• Met Office Hadley Centre (MOHC, UK)
• Institut Pierre Simon Laplace (IPSL, France)
• Meteorological Research Institute (MRI, Japan)

Short Summary

This study demonstrates that cloud radiative effects (CREs) significantly increase wintertime atmospheric blocking frequency in the Euro-Atlantic sector. This occurs by enhancing upstream diabatic wave activity sources, primarily through feedback on latent heating, which then promotes downstream wave activity convergence and blocking formation.

Objective

• To investigate how Cloud Radiative Effects (CREs) influence the frequency and dynamics of atmospheric blocking, particularly in the Euro-Atlantic sector.
• Principal Hypothesis: Cloud radiative effects (CREs) significantly increase the frequency of Euro-Atlantic atmospheric blocking by enhancing upstream diabatic sources of wave activity.

Study Configuration

• Spatial Scale: Euro-Atlantic sector (43°–65°N, 40°W–20°E), West/Central Europe (45°–60°N, 10°W–15°E), Northern Hemisphere mid-latitudes.
• Temporal Scale: Winter (December–February, DJF) climatology; 20-year simulations for E3SM experiments; MERRA-2 data from 1980 to 2020; CFMIP AMIP simulations from 1979 to 2014. Blocking events are defined to persist for at least five days.

Methodology and Data

• Models used:
  • U.S. DOE’s Energy Exascale Earth System Model v1 (E3SMv1)
  • Cloud-Feedback Model Intercomparison Project (CFMIP) COOKIE-2 simulations (CESM2-amip, HadGEM-amip, IPSL-amip, MRI-amip, and their LWOFF counterparts).
• Data sources:
  • Numerical experiments: Control (CTL), Cloud-Locking (CLOCK), and Longwave Cloud Radiative Effect-Off (LWOFF) simulations using E3SMv1, with prescribed annually repeating sea surface temperatures (SSTs) and sea-ice concentrations based on year 2000 climatology.
  • Reanalysis: NASA MERRA-2 dataset (1980-2020) for validation.
  • Blocking detection: Dole and Gordon’s anomaly-based blocking index, using daily 500-hPa geopotential height (Z500) anomalies exceeding the 90th percentile, covering at least 2 x 10^6 square kilometers, and persisting for a minimum of five days.
  • Diagnostics: Finite-amplitude Local Wave Activity (LWA) budget analysis, Eady growth rate (EGR), and Plumb flux for quasi-stationary waves.

Main Results

• Interactive CREs significantly increase the Euro-Atlantic blocking frequency by up to 1.67% blocked days per winter.
• Disabling interactive CREs (CLOCK experiment) reduces mid-latitude Euro-Atlantic blocking frequency by up to 21.60% ± 2.14%.
• Disabling Longwave CREs (LWOFF experiment) reduces mid-latitude Euro-Atlantic blocking frequency by approximately 37.26% ± 3.42%.
• Multi-model experiments from CFMIP COOKIE-2 corroborate these findings, showing an average reduction of 15% to 19% in blocking frequency when LWCREs are disabled.
• CREs enhance upstream diabatic wave activity sources (h_Ai cos ϕ) in the Warm Conveyor Belt (WCB) region, both directly through longwave heating and indirectly through a dominant feedback on latent heating (LH).
• The enhanced LWCRE in the mid-troposphere amplifies large-scale ascent and poleward moisture transport in the WCB, leading to increased LH.
• This increased upstream diabatic wave activity is then advected downstream by the zonal flow and converges, promoting localized blocking formation.
• Changes in CREs also indirectly influence blocking by modifying the background mean state: disabling LWCRE leads to a more pronounced poleward jet shift, a stronger weakening of quasi-stationary ridges over Europe, reduced low-level baroclinicity (Eady growth rate), and weaker climatological moisture transport, all creating conditions unfavorable for blocking.

Contributions

• This study is the first to apply the cloud-locking technique to investigate the impact of Cloud Radiative Effects (CREs) on atmospheric blocking.
• It identifies CREs as a significant, previously underexplored, factor increasing Euro-Atlantic blocking frequency.
• It elucidates the mechanism by which CREs enhance blocking: by amplifying upstream diabatic wave activity sources, primarily through a positive feedback on latent heating within Warm Conveyor Belts.
• The findings underscore the critical necessity of accurately representing cloud-radiation interactions in weather and climate models for improved simulation and prediction of blocking events.
• It extends existing understanding of the role of moist processes in blocking by highlighting the crucial contribution of cloud-radiation interactions in the WCB.

Funding

• U.S. Department of Energy Office of Science Biological and Environmental Research (Global and Regional Model Analysis program area).
• Pacific Northwest National Laboratory (PNNL) operated by Battelle for the U.S. Department of Energy under Contract DE-AC05-76RL01830.
• National Energy Research Scientific Computing Center (NERSC), a U.S. Department of Energy Office of Science User Facility, operated under Contract No. DE-AC02-05CH11231.
• Impetus4Change (I4C; grant 101081555), NextGEM (grant 101057527), and Nor-ESM4CMIP7 (RCN grant 352204) projects, funded by the Research Council of Norway (RCN) under the European Union’s Horizon Europe research and innovation programme.

Citation

@article{Lubis2025Cloud,
  author = {Lubis, Sandro W. and Harrop, Bryce E. and Lu, Jian and Leung, L. Ruby and Chen, Ziming and Huang, Clare S. Y. and Omrani, Nour‐Eddine},
  title = {Cloud radiative effects significantly increase wintertime atmospheric blocking in the Euro-Atlantic sector},
  journal = {Nature Communications},
  year = {2025},
  doi = {10.1038/s41467-025-64672-9},
  url = {https://doi.org/10.1038/s41467-025-64672-9}
}