Abstract:
The Atlantic multidecadal oscillation (AMO) is considered as one of the major drivers of Indian Summer monsoon (ISM) multidecadal variability. The teleconnection is thought to take place via two dominant pathways—by generating upper-level circulation and heating responses across Eurasia and via the Atlantic-Pacific atmospheric bridge mechanism and associated modulations of Hadley-Walker circulations. Using the PMIP3 Last millennium (LM) simulations, the current study investigates these pathways in five models which exhibit a significant positive correlation between AMO and ISM. In all the models, the upper-level wave responses associated with the AMO are found to be inadequate to induce positive tropospheric temperature (TT) anomalies over the ISM domain. In the four models which capture the AMO modulation of summer North Atlantic Oscillation (SNAO) variability, major discrepancies are observed in the SNAO downstream TT responses. The extratropical-tropical Pacific SST gradient is a critical aspect of the Atlantic-Pacific atmospheric bridge mechanism. A positive correlation is observed between the AMO and the Pacific SST gradient in all the models and the associated Walker circulation response is also captured in the LM simulations. Thus while the upper-level circulation and TT responses involved in the Eurasian pathway, are not captured by most of the models, the Pacific pathway emerges as a better represented teleconnection pathway in the LM simulations. Reliability of decadal climate predictions of ISM largely depends on the fidelity of global models in simulating these teleconnection mechanisms and the current study highlights some of the main deficiencies in the model simulated teleconnection processes.