Impact of aerosol absorption and scattering on winter fog lifecycle: insights from NWP simulations over Indo-Gangetic Plains

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 on the development and evolution of dense fog over the IGP using high-resolution numerical experiments. We focus especially on the relative contributions of absorption and scattering to aerosol-radiation interactions (ARI). 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. Satellite-derived absorbing aerosol indices confirmed the presence of absorbing aerosols over the study region. The results of numerical experiments reveal that disabling the aerosol absorption component of ARI nearly doubled the area affected by dense fog, increased fog height by more than 20 %, and delayed fog dissipation by about 2 h. In contrast, turning off the scattering component of ARI reduced fog coverage by 18 %. 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 emphasise the need to accurately represent ARI in numerical weather prediction models for improved fog forecasting over aerosol-rich regions like the IGP.