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Abstract:
This study presents a detailed analysis of the 2019 record-breaking seasonal (June-September) monsoon rainfall, since 1901, over large areas of Western India, which evolved in the backdrop of an intense positive Indian Ocean Dipole (p-IOD) event. Analysis of multi-source observational datasets (rain gauge, GPM, NOAA, ERA5) reveals that the 2019 unusually excessive and flood-producing monsoonal rains over Western India markedly came from three intense rain episodes (IREs) viz., 1) 28th June - 12th July 2) 24th July -11th August 3) 2nd September – 13th September and was characterised by large-scale bands of organised convection. We observe a preponderance of stratiform precipitating mesoscale convective systems embedded within the organised rainband. Regression analyses of various atmospheric fields were performed to understand the dominant spatial structures during the IRE days. Our findings indicate that the continual top-heavy stratiform heating forced a Rossby-wave pattern with regional stretching of mid-tropospheric potential vorticity across South and Southeast Asia. Results show that the pIOD-induced enhanced cross-equatorial moisture transport fostered deep convection and heavy precipitation in this region. This study highlights the potential ramifications of intense pIOD manifestations on IREs and their hydrological consequences over the monsoon-centric areas of South and Southeast Asia in the 21st century.
