Weaker connection between the Atlantic Multidecadal Oscillation and Indian summer rainfall since the mid-1990s

Abstract

Previous studies have shown that the Atlantic Multidecadal Oscillation (AMO) can play an important role in modulating the variability of Indian summer monsoon rainfall (ISMR) over a 50–60-yr timescale. A significant positive correlation between the AMO and ISMR is found both in observations and models. However, instrumental records show that the relationship becomes non-significant or even of opposite sign after the mid-1990s, suggesting a weakening of the AMO–ISMR connection. The mechanism for the breakdown of the AMO–ISMR connection is investigated in the present work, and the results suggest that a substantial warming in the Indian–tropical western Pacific Ocean plays a role. The warming weakens the meridional gradient of tropospheric temperature between Eurasia and the Indian Ocean, and reduces the meridional sea level pressure gradient between the Indian Subcontinent and Indian Ocean, weakening the Indian summer monsoon. Thus, warming in the Indian–tropical western Pacific Ocean seems responsible for the weakened connection between the AMO and ISM.

摘要

以前的研究表明在50-60年的时间尺度上，北大西洋多年代际振荡（AMO）对印度夏季降水（ISMR）有重要的调制作用。在观测和模式研究中AMO和ISMR均存在显著的正相关关系。但是，上世纪90年代中期之后，器测资料显示二者的关系变得不显著，甚至表现出相反的位相关系。这表明二者的关系减弱了。这个研究探讨了AMO-ISMR关系减弱的可能物理机制。研究显示印度洋-热带西太平洋海温的显著增暖可能是原因之一。这个增暖使得欧亚大陆和印度洋之间的对流层温度梯度减弱，以及印度次大陆和印度洋之间的海陆热力差异减弱，从而减弱ISMR。

Keywords:

• Atlantic Multidecadal Oscillation
• Indian summer rainfall
• connection
• multidecadal variation

关键词:

• 北大西洋多年代际振荡
• 印度夏季降水
• 关系
• 多年代际变化