Assessing the relationship between atmospheric aerosols and maximum surface air temperature over the Indian region

Atmospheric aerosols significantly influence Earth’s climate through direct, indirect, and semi-direct effects on solar radiation. While their global cooling impact at the surface is well-documented, regional-scale studies using observations remain limited. This study quantifies aerosol impact on maximum surface air temperature over India, a region characterised by substantial diversity in aerosol types and seasonality, using long-term satellite observations, reanalysis datasets analysed with a multiple linear regression framework that accounts for cloud cover and atmospheric moisture, and complementary regional climate model simulations to validate the underlying physical mechanisms. Results reveal strong spatial variability in the aerosol effect (AER_EFFOBS) with the aerosols appearing to cool the surface by −0.25 °C in winter (DJF) and −0.04 °C in the post-monsoon (SON) while warming it by 0.15 °C in the pre-monsoon (MAM). This warming/cooling appears to be linked to aerosols and aerosol-induced changes in clouds. Analysis using reanalysis data (MERRA2) yields an aerosol effect (AER_EFFRA) of −0.45 °C in DJF, 0.18 °C in MAM, and −0.12 °C in SON matching the spatial patterns in AER_EFFOBS. Model simulations using the Regional Climate Model (RegCM 4.7.1) further corroborate the effect of aerosol-induced changes in low cloud cover affecting the temperature. These results underscore the intricate relationship between aerosol and surface temperature over India, a region with high aerosol loading, emphasizing the need for improved understanding of aerosol-cloud-climate interaction.