Abstract The interlinked Eastern Indian Ocean (EIO) and Western Pacific Ocean (WPO), known as the Indo-Pacific warm pool, are highly active regions for intraseasonal oscillations (ISOs). Interestingly, distinct behaviors exist in ISO seasonality in these two basins. In the WPO, ISO intensity peaks in winter, decays rapidly starting from spring and reaches a minimum in summer. While in the EIO, ISO intensity exhibits a bimodal distribution, with a stronger peak in spring and a weaker one in autumn, followed by two troughs in summer and winter, respectively. Here, the regional ISO seasonality is understood in view of the regional differences in the background fields. For the bimodal ISO seasonality in the EIO, the increase from winter to spring is primarily due to elevated moisture content, the decrease from spring to summer is due to the decline in moisture and the meridional variation in vertical wind shear, and the increase from summer to autumn is mainly attributed to the meridional variation in vertical wind shear. In the WPO, the significant winter-summer contrast is mainly caused by change in moisture content.

中文翻译：

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印度洋-太平洋季节内振荡的区域季节性

摘要 相互连接的东印度洋 (EIO) 和西太平洋 (WPO)，被称为印度洋-太平洋暖池，是季节内振荡 (ISO) 的高度活跃区域。有趣的是，这两个盆地的 ISO 季节性存在不同的行为。在 WPO 中，ISO 强度在冬季达到峰值，从春季开始迅速衰减，并在夏季达到最小值。而在 EIO 中，ISO 强度呈现双峰分布，春季峰值较强，秋季较弱，其次是夏季和冬季两个低谷。这里，区域ISO季节性是根据背景场的区域差异来理解的。对于 EIO 中的双峰 ISO 季节性，从冬季到春季的增加主要是由于水分含量升高，春季到夏季的减少是由于水分的减少和垂直风切变的经向变化，而夏季到秋季的增加主要是由于垂直风切变的经向变化。在 WPO 中，显着的冬夏对比主要是由水分含量的变化引起的。