"Unveiling the link: Fog evolution in the Indo-Gangetic Plain in presence of the Tropical cyclone"

The Indo-Gangetic Plain (IGP) experiences severe fog episodes predominantly during the peak winter months (December–February). However, the onset and dynamical drivers of fog during the pre-winter period (20 November to 15 December) remain relatively unexplored. This study investigates the teleconnections between North Indian Ocean Tropical Cyclones (TCs) and the evolution of widespread fog events over the IGP during this early winter phase. Utilizing 20 years (2000–2019) of multi-station visibility data, TC tracks, and ERA5 reanalysis, we establish a robust link between cyclonic activity and inland fog formation. Our analysis reveals that 12 TCs (11 in the Bay of Bengal, 1 in the Arabian Sea) coincided with widespread fog events, affecting approximately 30% to 56% of observational stations. Contrary to hypotheses suggesting direct moisture transport as the primary driver, we demonstrate that the modulation is dynamically driven by TC-induced large-scale subsidence. Composite diagnostics of Omega (vertical velocity) and geopotential heights reveal that active TCs trigger a distinct subtropical subsidence belt extending over the IGP. This enhanced mid-tropospheric subsidence (positive Omega anomalies) creates a strong stable layer that traps boundary layer moisture and suppresses vertical mixing, independent of the TC’s intensity. These findings identify a critical synoptic precursor for pre-winter fog, suggesting that monitoring TC-induced subsidence teleconnections can significantly improve early-season fog forecasting over the Indian subcontinent.