Investigating Concurrent Cyclonic Disturbances in the North Indian Ocean and Associated Large-Scale Atmospheric Influences

This study analyzed concurrent cyclonic disturbances (CCDs) that formed simultaneously over the Arabian Sea (AS) and Bay of Bengal (BOB) in the North Indian Ocean (NIO) considering the timeframe from 1960 to 2021. Using the best-track datasets from the India Meteorological Department, 14 CCD pairs were identified, with a frequency of 0.5 per year, indicating their rare occurrences. All pairs occurred during post-monsoon months, primarily in October and November. Large-scale meteorological features associated with four CCD events (in 1981, 2015, 2018, and 2020) were examined using multiple datasets, focusing on El Niño-Southern Oscillation (ENSO), Indian Ocean Dipole (IOD), Madden-Julian Oscillation (MJO), and convectively coupled equatorial waves (CCEWs). Enhanced convection and low-level westerlies were identified as precursors to CCD formation. The convective phase of MJO, particularly phase 3, was found to be highly conducive to CCD genesis. Tropical Disturbance and Equatorial Rossby waves significantly influenced cyclogenesis, especially in BOB, while AS exhibited variable conditions. Lower-level circulation anomalies, including vorticity and wind, initiated convection-circulation feedback critical to CCD development.