Synoptic-Scale Mechanisms And Climate Oscillation Influences On The Monsoon Breaks Of The Indian Summer Monsoon System

The Indian Summer Monsoon Rainfall (ISMR), occurring from the month of June to September, is characterized by intraseasonal variability in the form of active and break spells. Monsoon breaks are periods of sparse to no rainfall, marked by positive outgoing longwave radiation anomalies, above-normal pressures, and clear-sky conditions. These monsoon breaks can have socioeconomic impacts due to their effect on crop growth stages, irrigation planning, and water management. This study aims to investigate the synoptic-scale systems responsible for the onset and sustenance of monsoon breaks over the Western Ghats and other parts of India to improve future predictability of the same. Rainfall data from 1901 to 2025 is used to identify break spells and classify them into short, moderate, and long-duration events. Subsequently, decadal rainfall composites are constructed. These composites reveal patterns of rainfall suppression and enhancement over the Indian subcontinent, equatorial Indian Ocean and West Pacific. Although the spatial structure of rainfall anomalies remains consistent, slight decadal variabilities are observed. Composite analyses of outgoing longwave radiation, and upper and lower tropospheric winds are used to diagnose the synoptic features associated with monsoon breaks. Case studies of recent drought years, 2002 and 2015, highlight the role of upper tropospheric anticyclones, northward displacement of the monsoon trough, and dry air intrusion from West Asia in sustaining and prolonging the breaks, confirming previous studies. The influence of large scale climate oscillations such as ENSO, EQUINOO, and the Boreal Summer Intraseasonal Oscillation (BSISO) on monsoon break frequency and duration is investigated using statistical and machine learning tools, with the aim of informing the development of improved predictive frameworks for monsoon breaks.