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<p>The weak, non-significant correlation between East Asian summer monsoon (EASM) rainfall and the concurrent ENSO index has hindered the development of ENSO-based forecasts of EASM. We show that this apparent statistical independence does not stem from randomness, but rather from two opposing phase relationships between the Pacific-Japan (PJ) teleconnection pattern and ENSO. A positive PJ can be triggered by two distinct Indo-Pacific sea surface temperature (SST) anomaly patterns corresponding to opposite ENSO phases: a La Niña–related tripolar pattern and an El Niño–related dipolar pattern. This results in rainfall over most PJ-affected regions of East Asia being statistically uncorrelated with the ENSO index. The PJ teleconnection patterns generated under these two scenarios exhibit notable discrepancies in their spatial morphology. This study explains the unexpectedly weak ENSO–EASM correlations and provides guidance for EASM rainfall prediction based on summer ENSO conditions. It also indicates that studies investigating the impacts of <i>boreal summer-time</i> ENSO should account for the diverse tropical SST patterns associated with ENSO rather than relying solely on a single ENSO index.</p>

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Why the statistical relationship between east asian summer monsoon rainfall and the concurrent ENSO index is weak and nonsignificant

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年4月4日

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  • Yu Liang,
  • Lei Fan,
  • Hui-Huang Fu,
  • Chun Li,
  • Qinyu Liu

摘要

The weak, non-significant correlation between East Asian summer monsoon (EASM) rainfall and the concurrent ENSO index has hindered the development of ENSO-based forecasts of EASM. We show that this apparent statistical independence does not stem from randomness, but rather from two opposing phase relationships between the Pacific-Japan (PJ) teleconnection pattern and ENSO. A positive PJ can be triggered by two distinct Indo-Pacific sea surface temperature (SST) anomaly patterns corresponding to opposite ENSO phases: a La Niña–related tripolar pattern and an El Niño–related dipolar pattern. This results in rainfall over most PJ-affected regions of East Asia being statistically uncorrelated with the ENSO index. The PJ teleconnection patterns generated under these two scenarios exhibit notable discrepancies in their spatial morphology. This study explains the unexpectedly weak ENSO–EASM correlations and provides guidance for EASM rainfall prediction based on summer ENSO conditions. It also indicates that studies investigating the impacts of boreal summer-time ENSO should account for the diverse tropical SST patterns associated with ENSO rather than relying solely on a single ENSO index.