Modulations in the Indian Summer Monsoon-ENSO teleconnections by the North Tropical Atlantic

North Tropical Atlantic Sea Surface Temperature (i.e., NTA SST) anomalies emerge as a key-driver of the whole El Nino Southern Oscillation-Indian Summer Monsoon (ENSO-ISM) system. However, as the underlying physical mechanisms are not yet well understood, this study made an attempt to have deeper insights on the role of the NTA SST variability on the ISM, ENSO and their mutual relationships. The evidences from observations and a Pi-Control coupled simulation demonstrate the pronounced biennial nature of the NTA-ENSO-ISM system and suggest the precursory role of the NTA SSTs in this biennial ENSO-ISM system. As the cause-and-effect relationships are difficult to disentangle, ensembles of short coupled sensitivity experiments are conducted by imposing observed warm (cold) SST anomalies over NTA. These 1-year simulations start from various January initial conditions corresponding to strong El Nino (La Nina) events as identified from Pi-Control and subsequently impose warm (cold) SST anomalies over the NTA region after the El Nino (La Nina) peak in January. The sensitivity experiments support the hypothesis of a key role of NTA SSTs in the reversal of the ENSO conditions through their capacitor effect. They further illustrate the nonlinear characteristics of this system as cold NTA SST perturbations are more influential than warm NTA SSTs. This non-linearity brings up new perspectives on the NTA-ENSO-ISM system, as it is further reflected in the asymmetric response in the simulated ENSO-ISM, with the cold NTA perturbations initiated from the La Nina conditions showing a stronger anomalous ISM response during boreal summer, which is in contrast with the feeble ISM response in the warm NTA perturbations experiment using the El Nino initial conditions. This non-linearity of NTA-ENSO-ISM has larger implications in a global warming scenario, as the climate variability over NTA region is projected to intensify in the future.