Predictability of South-Asian monsoon rainfall beyond the legacy of Tropical Ocean Global Atmosphere program (TOGA)

In the backdrop of overwhelming evidences of associations between North-Atlantic (NA) sea-surface temperature (SST) and the Indian summer Monsoon Rainfall (ISMR), the lack of a quantitative nonlinear causal inference has been a roadblock for advancing ISMR predictability. Here, we advance a hypothesis of teleconnection between the NA-SST and ISMR, and establish the causality between the two using two different nonlinear causal inference techniques. We unravel that the NA-SST and the El Nino and Southern Oscillation (ENSO) are two independent drivers of ISMR with the former contributing as much to ISMR variability as does the latter. Observations and climate model simulations support the NA-SST–ISMR causality through a Rossby wave-train driven by NA-SST that modulates the seasonal mean by forcing long active (break) spells of ISMR.