Coherent response of the Indian Monsoon Rainfall to Atlantic Multi-decadal Variability over the last 2000 years

Abstract

Indian Summer Monsoon (ISM) rainfall has a direct effect on the livelihoods of two billion people in the indian-subcontinent. Yet, our understanding of the drivers of multi-decadal variability of the iSM is far from being complete. In this context, large-scale forcing of ISM rainfall variability with multi-decadal resolution over the last two millennia is investigated using new records of sea surface salinity (δ 18 Ow) and sea surface temperatures (SSts) from the Bay of Bengal (BoB). Higher δ 18 Ow values during the Dark Age Cold Period (1550 to 1250 years BP) and the Little Ice Age (700 to 200 years BP) are suggestive of reduced ISM rainfall, whereas lower δ 18 Ow values during the Medieval Warm Period (1200 to 800 years BP) and the major portion of the Roman Warm Period (1950 to 1550 years BP) indicate a wetter iSM. this variability in iSM rainfall appears to be modulated by the Atlantic Multi-decadal oscillation (AMO) via changes in large-scale thermal contrast between the Asian land mass and the Indian Ocean, a relationship that is also identifiable in the observational data of the last century. Therefore, we suggest that inter-hemispheric scale interactions between such extra tropical forcing mechanisms and global warming are likely to be influential in determining future trends in ISM rainfall.

Influence of climatic indices (AMO, PDO, and ENSO) and temperature on rainfall in the Northeast Region of India

“…However, the phase arrows in the significant area in the high-frequency region during 1950-2016 are randomly oriented, so its manifestation is not clear. The correlation between AMO and rainfall variability during 1960-2006 is consistent with Naidu et al [16]; however, the two records have not precisely matched temporally.…”

“…Like PDO, the AMO is the pattern of SSTs in the North Atlantic Ocean with periodicities of 55-80 years [62]. The AMO has been suggested to play a significant role in modulating ISMR on a decadal to a multi-decadal scale [14][15][16]. In a study, Malik et al [15], using a long data record of 400 years, reported that the modulation of ISMR on a decadal to multi-decadal scale has influenced by the integrated effect of AMO, PDO, and TSI (Total Solar Irradiance).…”

“…They noted that most of the dry events (decades) of ISMR occur during the simultaneous negative phase of TSI, the negative phase of AMO, and the positive phase of PDO. Naidu et al [16], utilizing sea surface salinity (δ18Ow) record of period 2000 years from the Bay of Bengal, reported that the multi-decadal variations of Indian summer rainfall (ISM) influenced by the phase of AMO. The overall increased rainfall over the Indian subcontinent has related to AMO's positive (warm) phase.…”

“…In contrast, its correlation with Total Solar Irradiance and AMO is not stationary on a decadal to multi-decadal scale. In another study, Naidu et al [16], using sea surface salinity and sea surface temperature data for the last 2000 years of Bay of Bengal, reported that the variability of Indian Summer Monsoon rainfall has modulated with AMO via changes in thermal contrast between the Indian Ocean and Asian landmass.…”

Corals Reveal an Unprecedented Decrease of Arabian Sea Upwelling During the Current Warming Era

“…The thermal contrast between the Indian subcontinent and the Indian Ocean drives the Indian monsoon circulations (Naidu et al., 2020; Roxy et al., 2015; Schott & McCreary, 2001; Wu et al., 2012). The southwest Indian monsoon (SW monsoon, Figure ) typically peaks in boreal summer (July and August) and provides most of the total annual rainfall on the Indian subcontinent.…”