Role of Smoke Aerosols in Governing Winter Time Lowlevel Cloud Properties Over the Indian Region

Abstract

The influence of smoke aerosols on the low-level clouds over the Indian landmass during winter is examined using fifteen years (2005–2019) of long-term multi-satellite and reanalyses observations. Climatologically higher values of aerosol optical depth (AOD) (> 0.6), Angstrom exponent (> 1.5), UVaerosol index (> 0.7), and black carbon and organic carbon (BC + OC) extinction aerosol optical thickness (EXTAOT) (> 0.18) are observed over the Indo-Gangetic Plain (IGP) compared to the rest of India. It indicates the dominance of carbonaceous aerosols over the IGP region. However, noticeable rise in AOD (~ 60%) and (BC + OC) EXTAOT (20–40%) are found over eastern parts of India, particularly Odisha and Chhattisgarh, and central-south India compared to IGP (< 10% and < 5% respectively) in the recent years. Interestingly, fire activities are also increasing over these areas and it neighborhood. This rise in aerosol loading over eastern and central-south India could be due to long-range transport from the northwestern parts and beyond and local anthropogenic emissions, including biomass burning. Besides, a significant enhancement in cloud fraction (CF) (50–60%) is noticed in and around the regions, where smoke aerosols increased considerably, implying the possible influence of smoke aerosols on the cloud properties. The present study suggests that low-level clouds persisted over most parts of the considered area during wintertime. While CF and cloud effective radius showed a noticeable increase in the polluted condition, cloud optical thickness and liquid cloud water path decreased with increase in aerosol loading. CALIPSO images suggest that a mixture of dust, polluted dust, and polluted continental/smoke aerosols dominated over the inland areas, mostly confined within 2 km altitude over the considered region. However, an elevated layer of absorbing aerosols (smoke and polluted dust) over the low-level cloud supports increased CF through the 'aerosol-cloud-boundary layer' feedback mechanism.