Investigating the Atlantic-monsoon teleconnection pathways in PMIP3 Last Millennium Simulations

Abstract The Atlantic multidecadal oscillation (AMO) is considered as one of the major drivers of Indian Summer monsoon (ISM) multidecadal variability, but the exact mechanism of teleconnection remains elusive. AMO can impact the ISM dominantly by two pathways – by generating upperlevel circulation and heating responses across Eurasia and via the Pacific through the atmospheric bridge mechanism and associated modulations of Hadley-Walker circulations in the Indo-Pacific. Using the PMIP3 Last millennium (LM) simulations, the current study investigates the AMO-ISM teleconnection in the context of these pathways of interaction. A significant positive correlation is observed between AMO and ISM in five of the eight models. While the models display only limited skill in simulating the upper-level circulation and tropospheric temperature responses involved in the Eurasian pathway, they exhibit better skill in capturing the Pacific SST responses induced by the AMO. Four of the five models capture the AMO modulation of summer North Atlantic Oscillation (SNAO), but major discrepancies are observed in the SNAO downstream responses. CCSM4 and MPI exhibit better skill in simulating the AMO forced upper-level circulation responses across Eurasia, while CSIRO, GISS and MRI-CGCM3 exhibit better skill in simulating the AMO modulation of extra tropical-tropical SST gradient over the Pacific. Reliability of decadal climate predictions of ISM largely depends on the fidelity of current generation global models in simulating the teleconnection mechanisms which modulate the ISM multidecadal variability, and results from the current study helps in highlighting some of the main deficiencies in model simulated teleconnection processes.