Indian Summer Monsoon System: A Holistic Approach for Advancing Monsoon Understanding in a Warming World

Abstract

The Indian Summer Monsoon (ISM), fondly known as just Monsoon, has invoked prose, poetry and music for millennia. And yet, it manages to produce surprises literally each year. Much progress has been made in the process and predictive understanding of the monsoon, but the ISM still remains a grand challenge for modelling, predictions and projections. The main thrust here is that the ISM has been studied piecewise for its onset, active/break events, seasonal total, extremes and the withdrawal along with the relation of each of these components with natural modes of climate variability and anthropogenic forcings. Even the concept of ISM being an integral part of the Inter-Tropical Convergence Zone (ITCZ) is incomplete in terms of the ITCZ context for the ISM onset, seasonal evolution and withdrawal. Neither is it clear how the seemingly intrinsic scale selection of the active/break periods can be explained by the ITCZ dynamics. An attempt is made here to consider the ISM as a system with these different components, viz. the onset, withdrawal, length of the rainy season, active/break periods, northward propagating systems and extremes. The ISM system (ISMS) framework is posited to be the most holistic way for further advancing the understanding of the ISM-ITCZ complex as well as the response of this complex to global warming. The ISMS concept should allow for the large-scale dynamics, thermodynamics and the global teleconnections that modulate ISM at various timescales to be comprehensively understood. This especially critical for eliciting a complete picture of how the active/break periods are being selected as the intrinsic timescales of ISMS, how this scale selection is being modulated by global warming and the local and remote mechanisms generating the extreme events. Unfortunately, the spatial distribution of rainfall within the subcontinent remains beyond the scope of this framework at this stage.