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<p>Daily precipitation anomalies in the western North Pacific (WNP) and East Asia (EA) exhibit significant intraseasonal variability, peaking at 10–30-day time scales. It has been suggested that boreal summer intraseasonal oscillation (BSISO) on 30–60-day time scales is strongly modulated by El Niño–Southern Oscillation (ENSO) with stronger intensity and propagation during La Niña compared to El Niño summers, but the dependency of 10–30-day BSISO on ENSO has not been well understood. Here, we show that the intensity and northward propagation of the 10–30-day BSISO convection over the WNP-EA region are stronger and more organized during El Niño developing summers than other summers, including neutral summers. During El Niño developing summers, the BSISO-induced precipitation and low-level circulation tend to exhibit a stronger meridional tripolar pattern than those during neutral summers. We highlight that the strengthening of 10–30-day BSISO northward propagation and associated rainfall anomalies over EA in El Niño developing summers is contributed by not only the previously proposed stronger air–sea interaction with a larger meridional gradient of sea surface temperature, but also an enhanced dynamic process with stronger relative vorticity and moisture convergence.</p>

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Modulation of 10–30-day Boreal Summer Intraseasonal Oscillation and Associated Rainfall Events by El Niño

  • 期刊论文

  • 发表日期：

    2025年7月16日

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  • Doo Young Lee,
  • June-Yi Lee,
  • Young-Min Yang,
  • Pang-Chi Hsu,
  • A-Young Lim

摘要

Daily precipitation anomalies in the western North Pacific (WNP) and East Asia (EA) exhibit significant intraseasonal variability, peaking at 10–30-day time scales. It has been suggested that boreal summer intraseasonal oscillation (BSISO) on 30–60-day time scales is strongly modulated by El Niño–Southern Oscillation (ENSO) with stronger intensity and propagation during La Niña compared to El Niño summers, but the dependency of 10–30-day BSISO on ENSO has not been well understood. Here, we show that the intensity and northward propagation of the 10–30-day BSISO convection over the WNP-EA region are stronger and more organized during El Niño developing summers than other summers, including neutral summers. During El Niño developing summers, the BSISO-induced precipitation and low-level circulation tend to exhibit a stronger meridional tripolar pattern than those during neutral summers. We highlight that the strengthening of 10–30-day BSISO northward propagation and associated rainfall anomalies over EA in El Niño developing summers is contributed by not only the previously proposed stronger air–sea interaction with a larger meridional gradient of sea surface temperature, but also an enhanced dynamic process with stronger relative vorticity and moisture convergence.