Wang et al. (2025) Enhanced El Niño–Southern Oscillation impact on Somali jet under greenhouse warming

Identification

• Journal: Climate Dynamics
• Year: 2025
• Date: 2025-12-15
• Authors: Haodong Wang, Tao Geng, Wenju Cai, Shuo Wu, Xiaopei Lin
• DOI: 10.1007/s00382-025-07988-y

Research Groups

• State Key Laboratory of Physical Oceanography/Frontiers Science Center for Deep Ocean Multispheres and Earth System/Sanya Oceanographic Institution, Ocean University of China, Qingdao, China
• Laoshan Laboratory, Qingdao, China
• Ocean Dynamics Processes and Climate Department, Qingdao Marine Science and Technology Center, Qingdao, China
• Academy of Future Ocean, Ocean University of China, Qingdao, China

Short Summary

This study reveals that the influence of El Niño–Southern Oscillation (ENSO) on the Somali Jet (SMJ) is projected to strengthen significantly in the 21st century under greenhouse warming, leading to increased risks of extreme rainfall events over South Asia.

Objective

• To examine how the connection between the El Niño–Southern Oscillation (ENSO) and the Somali Jet (SMJ) changes in response to greenhouse warming, and to elucidate the underlying mechanisms and implications for South Asian climate.

Study Configuration

• Spatial Scale: Global climate models focusing on the Northwestern Indian Ocean (30°–80° E, 10° S–20° N), tropical Pacific (5° S–5° N, 170°–120° W for Niño3.4 index), and Indian Ocean (50° E–70° E, 10° S–10° N and 90° E–110° E, 10° S–0° for IOD index), with specific attention to the Indian subcontinent (70° E–85° E, 7° N–30° N) and Maritime Continent.
• Temporal Scale: Analysis of historical (1900–1999) and future (2000–2099) periods under a high emission scenario (SSP5-8.5), with observational data from 1980–2023. Focus on the May-June-July (MJJ) season.

Methodology and Data

• Models used: 40 climate models from the Coupled Model Intercomparison Project Phase 6 (CMIP6) under the Shared Socioeconomic Pathway scenario 5-8.5 (SSP5-8.5).
• Data sources:
  • ECMWF Reanalysis v5 (ERA5) for observed monthly sea surface temperature (SST), wind, and precipitation (1980–2023).
  • CMIP6 model outputs for monthly SST, wind, and precipitation (1900–2099).
  • Somali Jet (SMJ) index derived from Multivariate Empirical Orthogonal Function (MV-EOF) analysis of 850 hPa zonal and meridional wind anomalies in the northwestern Indian Ocean.
  • Niño3.4 index for ENSO (SST anomaly in 5° S–5° N, 170°–120° W).
  • Dipole Mode Index (DMI) for IOD (SST gradient between tropical western and eastern Indian Ocean).
  • Standardized Precipitation Index (SPI) for identifying extreme wet and dry events over land.
  • Statistical significance assessed using a bootstrap method and two-tailed Student’s t-test.

Main Results

• The ENSO–SMJ connection is projected to increase significantly in the 21st century under greenhouse warming, with 70% of CMIP6 models showing an increased correlation. The multi-model ensemble mean increase is 14.9%.
• This strengthening is primarily attributed to an enhanced atmospheric teleconnection from ENSO to SMJ, rather than SMJ influencing ENSO.
• Under warming, intensified ocean-atmosphere coupling in the tropical Pacific leads to a larger zonal wind response to SST anomalies, with a 30.6% increase in tropical Pacific zonal wind sensitivity to Niño3.4 SST anomalies.
• This enhanced Pacific wind response propagates to the Indian Ocean, enlarging El Niño (La Niña)-induced easterly (westerly) wind anomalies, which consequently dampen (strengthen) the SMJ.
• Increased ENSO SST variability, projected by 80% of the models, further amplifies this enhanced influence.
• The Indian Ocean Dipole (IOD) can act as a conduit for ENSO's impact on SMJ if ENSO–IOD coupling strengthens, but the IOD–SMJ relationship itself does not show a significant change under warming.
• The strengthened ENSO–SMJ connection leads to a heightened risk of extreme wet and dry events over South Asia, particularly the Indian subcontinent. The number of extreme dry/wet events over India is projected to increase by 248 from the 20th to 21st century.
• The conditional probability of co-occurrence of SMJ anomalies and extreme precipitation events over India increases by 11.3% under ENSO conditions.

Contributions

• Provides a robust projection of an increased ENSO–SMJ teleconnection under greenhouse warming using a comprehensive ensemble of CMIP6 models.
• Elucidates the primary mechanisms behind this enhanced connection, highlighting the role of intensified ocean-atmosphere coupling in the tropical Pacific and increased ENSO variability.
• Clarifies the modulating role of the Indian Ocean Dipole, distinguishing its potential as a conduit for ENSO's impact from its own changing relationship with the SMJ.
• Quantifies the significant implications for increased frequency and risk of extreme rainfall events over South Asia, underscoring the importance of ENSO in future regional climate change predictions and adaptation strategies.

Funding

• National Natural Science Foundation of China (NSFC) project (42576208 and 42206209)
• Taishan Scholars Program (tsqn202312282)

Citation

@article{Wang2025Enhanced,
  author = {Wang, Haodong and Geng, Tao and Cai, Wenju and Wu, Shuo and Lin, Xiaopei},
  title = {Enhanced El Niño–Southern Oscillation impact on Somali jet under greenhouse warming},
  journal = {Climate Dynamics},
  year = {2025},
  doi = {10.1007/s00382-025-07988-y},
  url = {https://doi.org/10.1007/s00382-025-07988-y}
}