The variability of Indian Ocean shallow meridional overturning circulation (SMOC) is studied using the century long ocean reanalysis simple ocean data assimilation (SODA) data. Though SMOC exhibits stronger southward transport during boreal summer, it displays stronger variability during boreal winter. The spectrum analysis of winter SMOC index reveals presence of highest amplitude between 5 to 7 years at 95% confidence level, suggesting the dominance of intra-decadal SMOC variability. The robustness of intra-decadal SMOC variability is also confirmed in different ocean reanalysis data sets. Composite analysis of filtered upper Ocean Heat Content, sea level, thermocline depth and Sea Surface Temperature anomalies for strong (weak) SMOC years show negative (positive) anomaly over north and East of Madagascar. Correlation analysis, of filtered SMOC index and sea level pressure (zonal winds) over the India Ocean, found significant negative (positive) correlation coefficient north of 40 °S (around 10 °S) and significant positive (negative) correlation coefficient over the 45 °S to 70 °S (20 °S to 50 °S and north of 5 °S). This meridional pattern of correlation coefficient for sea level pressure, manifesting the out of phase relationship between sub-tropics and high latitude mean sea level pressure, resembles with Southern Annular Mode (SAM). We conclude that the intra-decadal variability of mean sea level pressure leads to zonal wind variation around 10 °S modulating SMOC, which in turn affects the upper ocean thermal properties in the east and north of Madagascar. This study for the first time brought out coherent intra-decadal evolution of SAM and SMOC during boreal winter.

印度洋浅经向翻转环流（SMOC）的变化是利用百年海洋再分析简单海洋数据同化（SODA）数据研究的。虽然 SMOC 在北方夏季表现出更强的向南传输，但在北方冬季表现出更强的变化。冬季 SMOC 指数的频谱分析显示，在 95% 的置信水平下，存在 5 至 7 年之间的最高振幅，表明年代内 SMOC 变异性占主导地位。在不同的海洋再分析数据集中也证实了年代际 SMOC 变化的稳健性。对强（弱）SMOC 年份过滤后的上层海洋热含量、海平面、温跃层深度和海面温度异常的综合分析显示，马达加斯加北部和东部出现负（正）异常。相关性分析，经过滤的 SMOC 指数和印度洋上空的海平面压力（纬向风），发现 40°S 以北（约 10°S）的显着负（正）相关系数和 45°S 至 45°S 的显着正（负）相关系数70 °S（20 °S 至 50 °S 和 5 °S 以北）。这种海平面压力相关系数的经向模式，表现出亚热带和高纬度平均海平面压力之间的反相关系，类似于南方环形模式（SAM）。我们得出结论，平均海平面压力的年代际变化导致 10 °S 左右的纬向风变化调节 SMOC，进而影响马达加斯加东部和北部的上层海洋热特性。这项研究首次揭示了 SAM 和 SMOC 在北方冬季的一致年代内演化。