Xie et al. (2025) Asymmetric Impacts of Extreme Positive and Negative Indian Ocean Dipole Events on Late‐Summer Monsoon Rainfall in Western South Asia

⚠️ Warning: This summary was generated from the abstract only, as the full text was not available.

Identification

• Journal: Geophysical Research Letters
• Year: 2025
• Date: 2025-12-02
• Authors: Mingmei Xie, Jia‐Zhen Wang, Hanjie Fan, Lei Zhang, Zhaohui Chen
• DOI: 10.1029/2025gl118671

Research Groups

Not explicitly mentioned in the abstract.

Short Summary

This study reveals that both extreme positive and negative Indian Ocean Dipole (IOD) events asymmetrically enhance rainfall over western South Asia during August–September, even when ENSO effects are removed, through distinct moisture convergence mechanisms driven by anomalous winds.

Objective

• To investigate how extreme positive and negative Indian Ocean Dipole (IOD) events influence South Asian monsoon rainfall, particularly over western South Asia, and to understand the underlying atmospheric mechanisms, independent of ENSO signals.

Study Configuration

• Spatial Scale: Indian Ocean basin, western South Asia, Bay of Bengal, Western Ghats.
• Temporal Scale: August–September (monsoon season), focusing on extreme IOD events.

Methodology and Data

• Models used: AGCM (Atmospheric General Circulation Model) simulations.
• Data sources: Observations (for initial relationship), AGCM simulations.

Main Results

• Both extreme positive IOD (EXpIOD) and extreme negative IOD (EXnIOD) events enhance rainfall over western South Asia during August–September, even after removing ENSO signals.
• EXpIOD enhances rainfall through a westward-extended Gill-type anticyclone, driven by suppressed convection over the eastern IOD pole, which reinforces background monsoon southwesterlies and promotes orographic rainfall near the Western Ghats.
• EXnIOD enhances rainfall through an eastward-shifted dipole, where positive convection in the east drives a cyclonic circulation transporting Bay of Bengal moisture westward, converging with cross-equatorial southwesterlies from the western IOD pole over western India.
• The influence of EXpIOD and EXnIOD on rainfall is asymmetric due to distinct atmospheric circulation patterns and moisture convergence mechanisms.

Contributions

• Reveals the asymmetric influence of extreme positive and negative IOD events on western South Asian rainfall, independent of ENSO.
• Identifies distinct atmospheric circulation and moisture convergence mechanisms for EXpIOD and EXnIOD leading to enhanced rainfall.
• Highlights the importance of considering pattern asymmetry between EXpIOD and EXnIOD for a comprehensive understanding of IOD-monsoon interactions.

Funding

Not explicitly mentioned in the abstract.

Citation

@article{Xie2025Asymmetric,
  author = {Xie, Mingmei and Wang, Jia‐Zhen and Fan, Hanjie and Zhang, Lei and Chen, Zhaohui},
  title = {Asymmetric Impacts of Extreme Positive and Negative Indian Ocean Dipole Events on Late‐Summer Monsoon Rainfall in Western South Asia},
  journal = {Geophysical Research Letters},
  year = {2025},
  doi = {10.1029/2025gl118671},
  url = {https://doi.org/10.1029/2025gl118671}
}