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<p>This study investigates the evolution of Indian Ocean Dipole (IOD) events in different seasonal phases and their impacts on East Asian summer rainfall, emphasizing the distinction of such responses to preceding IOD events. In general, unseasonable positive IODs are usually not attributable to sea surface temperature anomalies (SSTAs) in the tropical Pacific. In contrast, normal and prolonged pIODs are often accompanied by El Niño events. Particularly, the development of El Niño events plays a pivotal role in the triggering and development of normal pIODs. The prolonged pIOD and El Niño are both triggered by cold SSTAs south of the maritime continent (MC), and the two are synchronized from summer to autumn, thereby reinforcing each other. Both observations and model simulations reveal that the pattern of IOD-induced East Asian rainfall displays opposite meridional tripole spatial distributions between unseasonable and prolonged pIODs in boreal summer. During unseasonable pIODs, the heat source in the tropical western Indian Ocean induces an anticyclone in the East Asian subtropical region, transporting moisture to the Yangtze River Basin and leading to positive rainfall there. During prolonged pIODs, in contrast, the cold SSTAs south of the MC result in a positive Pacific-Japan (PJ) pattern, leading to negative (positive) summer rainfall anomalies in the Yangtze River Basin (South China).</p>

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The temporal evolutions of different types of Indian Ocean Dipole and their distinct impacts on East Asia summer rainfall

  • 期刊论文

  • 发表日期：

    2026年5月7日

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  • Yuan Xue,
  • Xiao-Tong Zheng

摘要

This study investigates the evolution of Indian Ocean Dipole (IOD) events in different seasonal phases and their impacts on East Asian summer rainfall, emphasizing the distinction of such responses to preceding IOD events. In general, unseasonable positive IODs are usually not attributable to sea surface temperature anomalies (SSTAs) in the tropical Pacific. In contrast, normal and prolonged pIODs are often accompanied by El Niño events. Particularly, the development of El Niño events plays a pivotal role in the triggering and development of normal pIODs. The prolonged pIOD and El Niño are both triggered by cold SSTAs south of the maritime continent (MC), and the two are synchronized from summer to autumn, thereby reinforcing each other. Both observations and model simulations reveal that the pattern of IOD-induced East Asian rainfall displays opposite meridional tripole spatial distributions between unseasonable and prolonged pIODs in boreal summer. During unseasonable pIODs, the heat source in the tropical western Indian Ocean induces an anticyclone in the East Asian subtropical region, transporting moisture to the Yangtze River Basin and leading to positive rainfall there. During prolonged pIODs, in contrast, the cold SSTAs south of the MC result in a positive Pacific-Japan (PJ) pattern, leading to negative (positive) summer rainfall anomalies in the Yangtze River Basin (South China).