Wei et al. (2026) Critical role of intraseasonal oscillations in shaping extreme rainfall from tropical cyclones over the South China Sea

Identification

• Journal: Weather and Climate Extremes
• Year: 2026
• Date: 2026-03-13
• Authors: Na Wei, Dajun Zhao, Qian Wang, L. X. Chen
• DOI: 10.1016/j.wace.2026.100890

Research Groups

• Nanjing Innovation Institute for Atmospheric Sciences, Chinese Academy of Meteorological Sciences–Jiangsu Meteorological Service
• State Key Laboratory of Severe Weather Meteorological Science and Technology, Chinese Academy of Meteorological Sciences
• National Meteorological Centre

Short Summary

This study quantifies the critical role of intraseasonal oscillations (ISOs), including the quasi-biweekly oscillation (QBWO) and Madden–Julian oscillation (MJO), in shaping extreme accumulated rainfall (EAR) from tropical cyclones (TCs) over the South China Sea (SCS), finding that ISOs contribute significantly to the occurrence and characteristics of these extreme events.

Objective

• Quantify the contributions of intraseasonal oscillations (ISOs) to tropical cyclone (TC) extreme accumulated rainfall (EAR) events.
• Identify dominant atmospheric circulation patterns associated with different ISO phase combinations during EAR events.
• Clarify the phase–amplitude configurations that regulate ISO-band contributions to TC-induced EAR.

Study Configuration

• Spatial Scale: South China Sea (0–22°N, 110–120°E) and southern coastal regions of China (mainland China and Hainan Island), with rainfall stations within a 500 km radius of TC centers.
• Temporal Scale: 1981–2021 (41 years).

Methodology and Data

• Models used: Not applicable (observational analysis using wavelet analysis).
• Data sources:
  • Daily precipitation data from 659 National Basic Meteorological Observatories (NBMOs) across mainland China and Hainan Island (National Meteorological Information Center (NMIC) of the China Meteorological Administration (CMA)).
  • Tropical cyclone best-track dataset (center positions, maximum sustained 10-meter wind speeds, minimum central pressure) from the Shanghai Typhoon Institute of the CMA (STI/CMA).
  • Fifth-generation European Centre for Medium-Range Weather Forecasts Reanalysis (ERA5) at 0.25° resolution.

Main Results

• Removing intraseasonal oscillation (ISO) components (10–20-day quasi-biweekly oscillation (QBWO) and 30–60-day Madden–Julian oscillation (MJO)) from rainfall signals causes 63%–78% of extreme accumulated rainfall (EAR) events to fall below the 295 mm threshold, demonstrating their critical contribution.
• EAR events are classified into three types based on dominant ISO signals: Type A (significant in both QBWO and MJO bands; 57.6%), Type B (QBWO-only dominant; 36.4%), and Type C (MJO-only dominant; 3.7%).
• ISO-related rainfall contributions decrease with increasing tropical cyclone (TC) intensity, indicating that weaker storms rely more heavily on favorable ISO phases for extreme rainfall.
• Peak rainfall in Type A and B events aligns with the QBWO crest (phase 0°), whereas in Type C events it coincides with the MJO's rising-to-peak phase (around 15°–20°).
• ISO-scale cyclonic circulations strengthen low-level westerlies south of the rainfall maximum, enhancing moisture convergence into the TC.
• QBWO-related circulation structures are similar in Type A and B events, characterized by northward-propagating cyclonic circulation. MJO-associated patterns in Type C events feature a more persistent and zonally extended moisture belt, developing from a zonally elongated belt of strong westerly anomalies.
• Type C events exhibit the longest median duration (7 days) and are confined to Hainan Island and southernmost Guangdong, coinciding with regions of significantly reduced TC translational speed.

Contributions

• Systematically quantifies the contribution of intraseasonal oscillations (QBWO and MJO) to tropical cyclone extreme accumulated rainfall events over the South China Sea.
• Provides a novel classification of EAR events based on the statistical significance of QBWO and MJO signals, revealing distinct characteristics and underlying dynamics for each type.
• Establishes robust observational evidence of phase-locking relationships between peak rainfall and specific phases of QBWO and MJO, and clarifies the associated circulation and moisture transport patterns.
• Highlights the inverse relationship between ISO-band rainfall contribution and TC intensity, suggesting a critical role for ISOs in generating extreme rainfall from weaker TCs.
• Offers a physical basis for improving extended-range prediction of high-impact hydrometeorological events in the SCS region.

Funding

• National Natural Science Foundation of China (42475012, 42175007)
• Basic Research Fund of Chinese Academy of Meteorological Sciences (2025XM001)
• Science and Technology Development Fund Project of the Chinese Academy of Meteorological Sciences (2024KJ017)
• State Key Laboratory of Severe Weather Meteorological Science and Technology (2025QZA18)
• CMA Innovation and Development Special Program (CXFZ2026J027, CXFZ2025Q004)
• Natural Science Foundation of Jiangsu Province (Grant BK20231108)

Citation

@article{Wei2026Critical,
  author = {Wei, Na and Zhao, Dajun and Wang, Qian and Chen, L. X.},
  title = {Critical role of intraseasonal oscillations in shaping extreme rainfall from tropical cyclones over the South China Sea},
  journal = {Weather and Climate Extremes},
  year = {2026},
  doi = {10.1016/j.wace.2026.100890},
  url = {https://doi.org/10.1016/j.wace.2026.100890}
}