Impact of Aerosol Absorption and Scattering on Winter Fog Lifecycle: Insights from NWP Simulations over Indo-Gangetic Plains

Abstract. The Indo-Gangetic Plains (IGP) of India frequently experience widespread and dense winter fog with substantial health and economic consequences. This season also coincides with elevated aerosol loading. This study investigates the influence of aerosols, particularly aerosol-radiation interactions (ARI), on the development and evolution of dense fog over the IGP, using high-resolution numerical experiments. While aerosol-cloud interactions related to fog have been extensively studied, the role of ARI has received relatively less attention, due to the limited prevalence of absorbing aerosols in many other parts of the world. However, the increasing number of absorbing aerosols over IGP prompted this study to isolate and examine the contributions of both scattering and absorbing components of ARI. The results of numerical experiments reveal that disabling aerosol absorption led to nearly doubling the area affected by dense fog, increasing fog height by ~20 %, and delaying fog dissipation by about two hours. In contrast, turning off the scattering reduced fog coverage by 18 %. Satellite-derived absorbing aerosol indices corroborated the model’s representation of strong absorption over the region. Another key insight is the contrasting influence of absorbing versus scattering aerosols on the vertical development of fog.  Scattering effects were spatially uniform, promoting the vertical growth of fog. Conversely, absorption had a spatially variable impact, enhancing or suppressing fog height depending on whether the absorbing aerosols resided within or above the boundary layer. These findings emphasize the need to accurately represent ARI in numerical weather prediction models for improved fog forecasting over aerosol-rich regions like the IGP.