The connection between the Atlantic Multidecadal Oscillation and the Indian Summer Monsoon since the Industrial Revolution is intrinsic to the climate system

Abstract

Observations show a significant positive correlation between the Atlantic Multidecadal Oscillation (AMO) and the Indian Summer Monsoon (ISM) over the past 100 years. Whether this connection is intrinsic to the climate system or caused by external forcing remains unclear in view of the substantial existence of anthropogenic greenhouse gases and aerosols in observations. Two state-of-the-art climate models (GFDL-CM3 and HadGEM2-ES), the historical simulations (1850-2005) of which show positive correlations between the AMO and ISM, similar to observation, are used to address this question. A significant positive AMO-ISM correlation exists in the control simulations with fixed preindustrial forcing with HadGEM2-ES, but not with GFDL-CM3. An in-depth analysis illustrates that the positive correlation in the HadGEM2-ES control run is more reasonable, since it simulates a similar teleconnection of the AMO with the North Pacific to that in both observations and previous studies. In comparison, the GFDL-CM3 control run fails to simulate the teleconnection of the AMO with the North Pacific. The positive AMO-ISM correlation in the historical simulation in GFDL-CM3 may be attributable to the role of the external forcing, since it is so strong that the AMO signals are excited additionally in the North Pacific. This study suggests that the AMO-ISM connection is intrinsic to the climate system, and highlights the crucial role played by the North Pacific in bridging such a connection.

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

“…The mid-and upper-tropospheric heating anomaly (Fig. 5c) features significant warming from the Atlantic across northern Africa to the Middle East and northern India, which intensifies the meridional thermal contrast between the continent and the Indian Ocean-a pattern consistent with several other modelling studies 45,46 . The regional circulation anomalies associated with the southwesterlies in the northern Indian Ocean are part of a hemispheric-wide response pattern to AMO variability featuring enhanced easterly trade winds across the northern equatorial Pacific and enhanced Walker cell north of the equator, leading to larger ascent (precipitation) over Indo-china and the Maritime Continent and subsequent changes in the meridional direction (regional Hadley circulation).…”

Effects of Anthropogenic Aerosol and Greenhouse Gas Emissions on Northern Hemisphere Monsoon Precipitation: Mechanisms and Uncertainty

“…Regional changes in temperature also contribute to the negative trend in precipitation. The cooling of the North Atlantic temperature is reminiscent of a negative phase of the Atlantic multidecadal variability (AMV) (Knight et al 2006;Krishnamurthy and Krishnamurthy 2014;Luo et al 2018;Monerie et al 2019b). The negative phase of the AMV and anomalously cold Mediterranean SSTs (Fig.…”

Central Continental Boreal Summer “Warming Holes” Modulated by Atlantic Multidecadal Oscillation Via Low‐Level Jets

“…This section attempts to explore the likely processes responsible for the causality relation. The AMO is known to influence rainfall, temperature and pressure in many regions of the Northern Hemisphere (Luo et al., 2018). It has been linked to rainfall and river flow anomalies over the U.S., increased drought occurrence over the Southwest and the North‐central U.S (McCabe et al., 2004).…”

“…A positive AMO phase has been shown to induce atmospheric responses like the summer North Atlantic Oscillation (NAO) pattern, leading to warming over the Eurasian continent and intensifying thermal contrast between the Indian sub‐continent and the tropical Indian Ocean and consequently stronger southwesterly Asian monsoon (Luo et al., 2018; Qian et al., 2014). The AMO can change surface thermal status over the Tibetan Plateau and increase Asian monsoon (Hu et al., 2004).…”