Decadal variability of climate over the Pacific and Atlantic Ocean is well studied. However, the decadal climate variability over the Indian Ocean and its possible impact on the summer monsoon received relatively less attention. The present study aims to explore the decadal variability of the Tropical Indian Ocean (TIO) sea surface temperature (SST) and its associations with the Indian summer monsoon rainfall (ISMR) variability. More than a hundred years of observed monthly SST data from Extended Reconstructed sea surface temperature and rainfall data from India Meteorological Department are used for the analysis. In addition to these, century reanalysis fields of winds, moisture, vertical velocity, tropospheric temperature, and sea level pressure are used for diagnosing different processes. Time series and wavelet analysis confirmed the presence of decadal variability (~ 9 to 30 years) in the TIO SST. The decadal variance of TIO SST is maximum in the eastern equatorial Indian Ocean, followed by the north Arabian Sea. Decadal EOF of TIO SST shows a dominant basin-wide mode explaining about 50% of total variance and has robust decadal variability during 1940 to 1952; wavelet analysis supported this robust signal statistically. Similar analysis for the ISMR reveals that the decadal variance of rainfall has significant strength over monsoon core zone and Western Ghats. The EOF analysis further confirms this spatial pattern of rainfall decadal variability over India. Correlation between of decadal TIO SST and over monsoon core zone (MCZ) rainfall is significant with 2 years lag. To understand how the decadal variability of TIO SST influences the ISMR, monsoon features during strong warm and cold phase are studied. During the warm phase, MCZ and Western Ghats receive more rain than normal and vice versa for cold phase. Which is consistent with strong southwesterly winds, strong pressure gradient, and strong convergence over the MCZ for the warm phase. Also, during the warm phase, positive anomaly of mid-troposphere temperature, vertical velocity, and moist static energy are found to be associated with excess convective activity. Apart from this, larger scale zonal (Walker) and meridional (Hadley) circulation fields are also in phase with the TIO SST and rainfall variability. Our study advocates that decadal variability in TIO SST influences the monsoon dynamics and moist thermodynamics leading to near in-phase changes in the rainfall over the MCZ and Western Ghats region.

对太平洋和大西洋气候的年代际变率进行了很好的研究。但是，印度洋上的年代际气候变化及其对夏季风的可能影响受到的关注相对较少。本研究旨在探讨热带印度洋（TIO）海表温度（SST）的年代际变化及其与印度夏季风降水（ISMR）变化的关系。分析使用了来自印度气象部门的扩展重构海表温度和降雨数据的一百多年观测到的每月SST数据。除这些之外，还使用了风，湿度，垂直速度，对流层温度和海平面压力的世纪再分析领域来诊断不同的过程。时间序列和小波分析证实了TIO SST年代际变化（约9至30年）的存在。TIO SST的年代际变化在赤道东印度洋最大，其次是北阿拉伯海。TIO SST的年代际EOF表现出占主导地位的全盆地模式，解释了总方差的50％，并且在1940年至1952年之间具有很强的年代际变化。小波分析在统计上支持了这种强大的信号。对ISMR的类似分析表明，降雨的年代际变化在季风核心区和西高止山脉具有明显的强度。EOF分析进一步证实了印度降水年代际变化的空间格局。十年TIO SST与季风核心区（MCZ）上空降水之间的相关性具有显着的滞后2年。为了了解TIO SST的年代际变化如何影响ISMR，研究了强暖和冷期的季风特征。在温暖期，MCZ和西高止山脉的降雨多于正常降雨，反之亦然。这与强西南风，强压力梯度和暖期MCZ上的强收敛是一致的。同样，在暖期，对流层中部温度，垂直速度和湿静能的正异常与过度对流活动有关。除此之外，更大范围的纬向（Walker）和子午（Hadley）环流场也与TIO SST和降雨变化性同相。