Contrasting Fog Dynamics between Urban and Rural Environments: Insights from Winter Observations over Delhi and Jewar

Widespread fog is a critical weather phenomenon over the Indo-Gangetic Plain (IGP) during winter, significantly impacting transportation safety and air quality. This study investigates the contrasting mechanisms of fog formation and dissipation over an urban site (Delhi) and a rural site (Jewar, ~80 km aerial distance) using extensive ground-based observations collected during the Winter Fog Experiment (WiFEX) field campaign from December 2023 to February 2024.

Analysis of WiFEX observations at Indira Gandhi International (IGI) Airport, Delhi, and Jewar Airport identified 15 dense fog events in Delhi and 25 in Jewar. The study highlights the influence of urbanization on fog dynamics, driven by a pronounced Urban Heat Island (UHI) effect in Delhi. This urban influence results in delayed fog formation and earlier dissipation compared to Jewar. The earlier onset and prolonged persistence of fog in Jewar are linked to stronger nocturnal cooling, greater moisture availability, and minimal urban heat retention. Jewar experienced a higher frequency of radiation fog events compared to Delhi, with visibility below a few meters persisting for several hours longer. Statistical analysis revealed distinct meteorological differences between the sites: nighttime surface temperatures were consistently lower in Jewar, while relative humidity peaked higher compared to Delhi. The extended fog duration in Jewar is attributed to sustained near-surface temperature inversion and weaker boundary layer mixing, in contrast to the urban environment.

These findings underscore the critical role of urbanization in modulating fog characteristics and highlight the importance of site-specific mitigation strategies for fog forecasting and management. This research advances ongoing WiFEX efforts to enhance fog prediction capabilities across the IGP, providing valuable insights for improving regional weather forecasting and mitigating societal impacts.