This study provides comprehensive analysis on the contrasting effects caused by the 1997 and 2015 historical El Niño events linked with the Indian Summer Monsoon (ISM) rainfall. The presence of strong southeast-northwest oriented cold Sea Surface Temperature (SST) anomalies during 1997, that spatially extended from southwest Pacific to Southeast Indian Ocean (SEIO) in comparison to the 2015 event is the robust feature. Evidently, these anomalies are closely related to interaction between cyclonic (anticyclonic) circulation over South Pacific Convergence Zone (south Australia). During 2015, the conjunction of Modoki II and classical El Niño triggered an asymmetrical equatorial circulation throughout the Indo-western Pacific (IWP) and thereby stimulated the Southern Annular Mode (SAM) through troposphere and stratospheric pathway mechanism. In addition, in 2015, SAM impacted the Indian Ocean, which intern affected ISM rainfall. Positive SAM associated with westward shift of anticyclone over south of Australia alters the circulation by inducing westerly winds over the South Indian Ocean, thereby suppressing Indian Ocean Dipole (IOD), and inducing drought conditions over India during 2015. Moreover, the AUS index, an indicator for IOD strength in boreal summer, is a bridging factor prevalent over mid-latitude regions in the southern hemisphere. Results from this study indicate the complex interaction of southern hemisphere atmospheric flow and its role in modulating the Indian Ocean region thereby ISM rainfall. A better understanding of these underlying mechanism can significantly enhance the predictive skills and projections of monsoon variability and extremes.

中文翻译：

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1997 年和 2015 年厄尔尼诺现象对印度夏季季风降雨的影响对比：南半球的作用


本研究全面分析了 1997 年和 2015 年历史上与印度夏季季风 （ISM） 降雨相关的厄尔尼诺事件引起的对比效应。与 2015 年事件相比，1997 年存在强烈的东南-西北方向的冷海面温度 （SST） 异常，在空间上从西南太平洋延伸到东南印度洋 （SEIO），这是一个强大的特征。显然，这些异常与南太平洋辐合带（南澳大利亚）上空的气旋（反气旋）环流之间的相互作用密切相关。2015 年，Modoki II 和经典厄尔尼诺现象的结合引发了整个印度-西太平洋 （IWP） 的不对称赤道环流，从而通过对流层和平流层途径机制刺激了南方环形模态 （SAM）。此外，在 2015 年，SAM 影响了印度洋，实习生影响了 ISM 降雨。2015 年，与澳大利亚南部反气旋西移相关的正 SAM 通过在南印度洋上诱发西风来改变环流，从而抑制印度洋偶极子 （IOD），并在 2015 年在印度引发干旱条件。此外，AUS 指数是北方夏季 IOD 强度的指标，是南半球中纬度地区普遍存在的桥接因素。这项研究的结果表明，南半球大气流动及其在调节印度洋地区从而影响 ISM 降雨方面的作用是复杂的相互作用。更好地了解这些潜在机制可以显着提高季风变化和极端值的预测技能和预测。