Sun et al. (2025) Role of nonlinear convection–SST sensitivity in shaping the southward displacement of westerly anomalies during El Niño peak phase

Identification

• Journal: Atmospheric Research
• Year: 2025
• Date: 2025-12-19
• Authors: Jingwen Sun, Jia Lu, Yifan Jia, Ruihuang Xie
• DOI: 10.1016/j.atmosres.2025.108712

Research Groups

• State Key Lab of Physical Oceanography/Frontier Science Center for Deep Ocean Multispheres and Earth System, and College of Oceanic and Atmospheric Sciences, Ocean University of China, Qingdao, China
• Inner Mongolia Climate Center, Inner Mongolia Meteorological Service, Hohhot, China
• Laboratory for Ocean Dynamics and Climate, Qingdao Marine Science and Technology Center, Qingdao, China

Short Summary

This study investigates the southward displacement of anomalous westerlies during the El Niño peak phase, revealing it is anchored by the seasonal migration of the tropical warm pool and regulated by a nonlinear convection-sea surface temperature (SST) relationship that enhances sensitivity south of the equator. The findings propose a synergistic framework where El Niño amplitude, convection-SST sensitivity, and warm pool background collectively shape El Niño-induced wind responses.

Objective

• To investigate the role of nonlinear convection-SST sensitivity in shaping the southward displacement of anomalous westerlies over the central equatorial Pacific during the El Niño peak phase.

Study Configuration

• Spatial Scale: Central equatorial Pacific, tropical warm pool region (specifically near 5°S for convection/westerly maxima), northern off-equatorial regions.
• Temporal Scale: Interannual variability (ENSO), El Niño peak phase (boreal winter), long-term simulations, historical periods (prior to 2000, since the early 21st century).

Methodology and Data

• Models used: UKESM1.0-LL (United Kingdom Earth System Model 1.0 - Low-Low resolution).
• Data sources: ERA5 reanalysis (European Centre for Medium-Range Weather Forecasts Reanalysis 5), observational data (implied for historical context).

Main Results

• The southward displacement of anomalous westerlies during the El Niño peak phase is anchored by the seasonal migration of the tropical warm pool, which enhances convection sensitivity to SST south of the equator.
• The spatial structure and intensity of westerly anomalies are regulated by a nonlinear convection–SST relationship, with sensitivity peaking within the 300.15 K–302.15 K (27 °C–29 °C) high SST range.
• Prior to 2000, stronger El Niño events were associated with more intense and spatially extensive southward-displaced westerly anomalies.
• Since the early 21st century, a La Niña–like mean-state change has weakened convection–SST sensitivity, leading to reduced magnitude and extent of westerly anomalies.
• The UKESM1.0-LL model successfully reproduced these relationships among southward-displaced westerly anomalies, El Niño amplitude, and convection-SST sensitivity.
• A synergistic framework is proposed: El Niño amplitude sets the scale of SST anomaly forcing, convection–SST sensitivity modulates the convective response, and the warm pool background constrains the spatial location of convection and associated wind anomalies.

Contributions

• Proposes a novel thermodynamic mechanism to explain the southward displacement of westerly anomalies during the El Niño peak phase.
• Complements existing dynamical explanations by highlighting the critical role of convection–SST sensitivity.
• Provides a comprehensive framework integrating El Niño amplitude, convection–SST sensitivity, and warm pool background in shaping El Niño-induced wind responses.

Funding

Not specified in the provided text.

Citation

@article{Sun2025Role,
  author = {Sun, Jingwen and Lu, Jia and Jia, Yifan and Xie, Ruihuang},
  title = {Role of nonlinear convection–SST sensitivity in shaping the southward displacement of westerly anomalies during El Niño peak phase},
  journal = {Atmospheric Research},
  year = {2025},
  doi = {10.1016/j.atmosres.2025.108712},
  url = {https://doi.org/10.1016/j.atmosres.2025.108712}
}