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<p>East Asian cold events (ECEs) frequently coincide with enhanced Madden-Julian Oscillation (MJO) convection over the eastern Indian Ocean (Phases 3–4). However, whether these cold anomalies are triggered by the concurrent MJO or by its preceding cycle [MJO (−1)] remains unclear. Using observations and reanalysis from 1979–2022, this study reveals a significant lagged response of East Asian cooling to the preceding MJO cycle. Moreover, when a prior MJO is present, the associated ECEs are markedly stronger, with surface cooling enhanced by approximately 1 K compared to events without a preceding MJO. This delayed response is linked to two dynamical pathways originating from MJO (−1). First, enhanced convection during MJO (−1) Phases 6–7 over the western Pacific excites a mid-latitude Rossby wave train, generating an anticyclone over Eurasia and transporting cold air toward East Asia via zonal temperature advection. Second, suppressed convection during MJO (−1) Phase 8 over the Maritime Continent drives a meridional overturning circulation, inducing adiabatic ascent and cooling over East Asia. Subseasonal hindcasts from the ECMWF S2S system confirm that the presence of a preceding MJO substantially improves prediction skill, extending useful lead time to ∼25 days, compared to ∼9 days when no prior MJO exists. These findings highlight the preceding MJO as a key driver of East Asian cold extremes and a critical source of their subseasonal predictability.</p>

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Preceding MJO enhances the subseasonal predictability of East Asian cold events via two dynamic pathways

  • 期刊论文

  • 发表日期：

    2026年3月12日

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  • Lu Wang,
  • Xuan Zhou,
  • Pang-Chi Hsu

摘要

East Asian cold events (ECEs) frequently coincide with enhanced Madden-Julian Oscillation (MJO) convection over the eastern Indian Ocean (Phases 3–4). However, whether these cold anomalies are triggered by the concurrent MJO or by its preceding cycle [MJO (−1)] remains unclear. Using observations and reanalysis from 1979–2022, this study reveals a significant lagged response of East Asian cooling to the preceding MJO cycle. Moreover, when a prior MJO is present, the associated ECEs are markedly stronger, with surface cooling enhanced by approximately 1 K compared to events without a preceding MJO. This delayed response is linked to two dynamical pathways originating from MJO (−1). First, enhanced convection during MJO (−1) Phases 6–7 over the western Pacific excites a mid-latitude Rossby wave train, generating an anticyclone over Eurasia and transporting cold air toward East Asia via zonal temperature advection. Second, suppressed convection during MJO (−1) Phase 8 over the Maritime Continent drives a meridional overturning circulation, inducing adiabatic ascent and cooling over East Asia. Subseasonal hindcasts from the ECMWF S2S system confirm that the presence of a preceding MJO substantially improves prediction skill, extending useful lead time to ∼25 days, compared to ∼9 days when no prior MJO exists. These findings highlight the preceding MJO as a key driver of East Asian cold extremes and a critical source of their subseasonal predictability.