Athira K S, Roxy M K, Dasgupta Panini, Saranya J S, Singh Vineet Kumar, Attada Raju
Centre for Climate Change Research, Indian Institute of Tropical Meteorology, Ministry of Earth Sciences, Pune, India.
Department of Earth and Environmental Sciences, Indian Institute of Science Education and Research Mohali, Punjab, India.
Sci Rep. 2023 Aug 4;13(1):12643. doi: 10.1038/s41598-023-38730-5.
The Indian summer monsoon rainfall (ISMR) exhibits significant variability, affecting the food and water security of the densely populated Indian subcontinent. The two dominant spatial modes of ISMR variability are associated with the El Niño Southern Oscillation (ENSO) and the strength of the semi-permanent monsoon trough along with related variability in monsoon depressions, respectively. Although the robust teleconnection between ENSO and ISMR has been well established for several decades, the major drivers leading to the time-varying relationship between ENSO and ISMR patterns across different regions of the country are not well understood. Our analysis shows a consistent increase from a moderate to substantially strong teleconnection strength between ENSO and ISMR from 1901 to 1940. This strengthened relationship remained stable and strong between 1941 and 1980. However, in the recent period from 1981 to 2018 the teleconnection decreased consistently again to a moderate strength. We find that the ENSO-ISMR relationship exhibits distinct regional variability with time-varying relationship over the north, central, and south India. Specifically, the teleconnection displays an increasing relationship for north India, a decreasing relationship for central India and a consistent relationship for south India. Warm SST anomalies over the eastern Pacific Ocean correspond to an overall decrease in the ISMR, while warm SST anomalies over the Indian Ocean corresponds to a decrease in rainfall over the north and increase over the south of India. The central Indian region experienced the most substantial variation in the ENSO-ISMR relationship. This variation corresponds to the variability of the monsoon trough and depressions, strongly influenced by the Pacific Decadal Oscillation and North Atlantic Oscillation, which regulate the relative dominance of the two spatial modes of ISMR. By applying the PCA-Biplot technique, our study highlights the significant impacts of various climate drivers on the two dominant spatial modes of ISMR which account for the evolving nature of the ENSO-ISMR relationship.
印度夏季风降水（ISMR）表现出显著的变率，影响着人口密集的印度次大陆的粮食和水安全。ISMR变率的两种主要空间模态分别与厄尔尼诺-南方涛动（ENSO）以及半永久性季风槽的强度和季风低压的相关变率有关。尽管ENSO与ISMR之间稳健的遥相关已被确立数十年，但导致该国不同地区ENSO与ISMR模式之间时变关系的主要驱动因素仍未得到很好的理解。我们的分析表明，1901年至1940年期间，ENSO与ISMR之间的遥相关强度从中等持续增加到极强。这种增强的关系在1941年至1980年期间保持稳定且强烈。然而，在1981年至2018年的近期，遥相关又再次持续下降至中等强度。我们发现，ENSO-ISMR关系在印度北部、中部和南部呈现出随时间变化的明显区域变率。具体而言，遥相关在印度北部呈增加关系，在中部呈减少关系，在南部呈稳定关系。东太平洋的暖海温异常对应着ISMR的总体下降，而印度洋的暖海温异常对应着印度北部降水减少和南部降水增加。印度中部地区在ENSO-ISMR关系中经历了最显著的变化。这种变化对应于季风槽和低压的变率，受太平洋年代际振荡和北大西洋振荡的强烈影响，它们调节着ISMR两种空间模态的相对主导地位。通过应用主成分分析-双标图技术，我们的研究突出了各种气候驱动因素对ISMR两种主要空间模态的显著影响，这解释了ENSO-ISMR关系的演变性质。
